JP4628046B2 - Semiconductor laser device and manufacturing method thereof, optical wireless communication transmitter, and optical disk device. - Google Patents

Description

  The present invention relates to a semiconductor laser element that requires high output and low driving power, a method for manufacturing the same, and a transmitter and an optical disc apparatus for optical wireless communication including such a semiconductor laser element.

  In recent years, with the development of IT technology and the spread of broadband, opportunities to handle large volumes of data such as voice and video regardless of time and place are increasing. In particular, the market for large-capacity data communication via space between indoor and outdoor fixed terminals connected to high-speed wired infrastructure and mobile portable terminals is expected to expand in the future. Carriers used for such wireless communication include radio waves and light, and the latter signal source currently uses LEDs because of its price and ease of handling. However, there is high expectation for optical wireless communication technology using a semiconductor laser element due to the demand for speeding up due to the secrecy of data and the increase in the amount of data. Based on such a situation, the standardization work of a new high-speed optical wireless communication standard using a semiconductor laser element is currently in progress.

  The wavelength of light used in this new optical wireless communication standard is a near infrared wavelength band with a wavelength of 1.0 μm or less centered on 850 to 950 nm. This is derived from the usage of emitting light into space, and is determined by the safety of the human body, especially the eyes, and the wavelength dependence of the light receiving element. It is necessary to develop a new semiconductor laser element that operates stably in this wavelength band. It becomes.

  However, since the near-infrared wavelength band of 1.0 μm or less is just in the middle of the wavelength band used in the short-wavelength optical disk device and the current long-wavelength optical fiber communication, these conventional wavelength bands were not a problem. There is a possibility that the structural parameters of the semiconductor laser element greatly affect the characteristics of the laser.

  Among such structural parameters, one of the parameters that greatly affects the efficiency of the semiconductor laser device is free electron absorption αfc in the semiconductor layer doped with impurities.

This is a phenomenon in which free electrons absorb light in the same valley in the energy band of the valence band or conduction band and transition to a higher energy side, and the wavelength and free electron absorption αfc are used with the doping concentration as a parameter. As the lines (a) to (c) in FIG. 9 showing the relationship, the value of the free electron absorption αfc increases as the wavelength of light is longer and the doping concentration is higher. The relationship is sought theoretically,
αfc ∝ {N × (aλ ^1.5 + bλ ^2.5 + cλ ^3.5 )} / τ≈ (N × λ ^p ) / τ (1)
It is expressed. In this formula (1), N is the doping concentration, λ is the wavelength of light, a to c are coefficients of the wavelength λ having different indices, and τ is the carrier relaxation time. P, which is the index of λ on the rightmost side, varies depending on the degree of various scattering caused by acoustic / optical phonons and ionized impurities, and is generally about 3 to 3.5 in the case of III-V compound semiconductors.

As described above, since absorption by free electrons is proportional to the third power of the wavelength, long wavelength band semiconductor laser devices having a wavelength of 1.3 μm or more that have been conventionally used in optical fiber communication have been regarded as very problematic. One solution to this problem is disclosed in Patent Document 1 (Japanese Patent No. 2699848). In this example, in the InP-based laser, the doping concentration of the entire p-type conductivity type layer excluding the cap layer is set to a relatively low value of about 3 × 10 ¹⁷ cm ^{−3 to} 7 × 10 ¹⁷ cm ^−3. Free electron absorption is suppressed. The reason why the p-type doping concentration is specified here is that, when compared at the same doping concentration, free electron absorption by the p-type dopant has a greater influence than that by the n-type dopant.

On the other hand, the short wavelength semiconductor laser element used in the optical disk apparatus is unlikely to be affected by free electron absorption unlike the long wavelength semiconductor laser element, so that the doping concentration of the p-type conductivity type layer is 5 × 10 ^18. If it is about cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ or less, it has not been considered as a problem.

There have also been reports on free electron absorption of semiconductor laser elements in a wavelength band located between these short wavelength band and long wavelength band. For example, Non-Patent Document 1 (Appl. Phys. Lett. Vol. 69 No. 20, 1996) describes an n-InGaP cladding layer, an n-InGaAsP lower light guide layer, an undoped quantum well active layer on an n-GaAs substrate. , A p-InGaAsP upper light guide layer, a p-InGaP cladding layer, and an n-GaAs cap layer are sequentially laminated from the substrate side, and the active layer has a wavelength of 808 nm (InGaAsP / InGaAsP quantum well active layer) or 980 nm (InGaAs / GaAs quantum layer). There are descriptions of several types of broad area type semiconductor laser devices set to oscillate in a well active layer. In these semiconductor laser elements, an internal absorption αi = about 4 to 5 cm ⁻¹ has been experimentally obtained, but free electron absorption αfc is one of the factors constituting the internal absorption value by various studies. It is concluded that there is almost no influence.
Japanese Patent No. 2699848 Appl. Phys. Lett. Vol. 69 No. 20, 1996

However, in the example of the near-infrared wavelength semiconductor laser device described above, the p-type doping concentration excluding the cap layer is about 5 × 10 ¹⁷ cm ⁻³ , which is relatively similar to the above-described long-wavelength semiconductor laser device. Since it is set to a low value, the effect of free electron absorption in the wavelength band is not fundamentally affected as described, or is the effect of free electron absorption not manifested because the doping concentration is low, It cannot be determined from this example.

Incidentally, the doping concentration of the p-type conductivity type layer is set to a relatively low value of about 5 × 10 ¹⁷ cm ^{−3 as in} the example of the near-infrared wavelength band semiconductor laser element and the long wavelength band semiconductor laser element described above. In the semiconductor laser device, the influence of free electron absorption is reduced. On the other hand, various adverse effects are caused on the laser characteristics other than the efficiency, such as temperature characteristics, element resistance, and transverse fundamental mode oscillation. For example, in a semiconductor laser device in which the p-type doping concentration of both the light guide layer and the cladding layer is set to about 4 × 10 ¹⁷ cm ^{−3 to} 6 × 10 ¹⁷ cm ⁻³ , the barrier level of the p-type conductivity type layer against the carrier is The temperature characteristics of the laser are degraded because it is lower than the barrier level of the higher doped layer. In particular, in the case of a semiconductor laser device in the near-infrared wavelength band where the energy gap of the well layer is large and carrier leakage is likely to occur compared to the long wavelength band, the carrier blocking effect is good in layers other than the active layer such as the light guide layer and the cladding layer. However, it becomes a more serious issue.

Also in terms of device resistance, in a semiconductor laser device having a low doping concentration of about 4 × 10 ¹⁷ cm ^{−3 to} 6 × 10 ¹⁷ cm ⁻³ , the driving power is increased as the resistance value increases. When an element is introduced as a light-emitting component into an optical wireless communication device, other components in the device such as a laser driver may be loaded, or the upper limit of allowable power may be reduced, and the selection range of other circuit components may be narrowed.

  Also, under such a low p-type doping concentration, the carrier diffusion rate becomes slow, so that spatial hole burning is induced and the oscillation transverse mode becomes unstable. This raises the relative noise intensity of the semiconductor laser device and increases the code error rate during communication, which is a serious problem for the semiconductor laser device for communication.

  From the above, in order to determine the doping structure of the p-type conductivity type layer particularly in the near-infrared wavelength band of wavelength of 1.0 μm or less, the temperature characteristics and elements in a trade-off relationship with suppression of free electron absorption It is necessary to achieve both resistance and stability in the oscillation transverse mode. In particular, since it is unclear whether or not the effect of free electron absorption is in the near-infrared wavelength band of 1.0 μm or less, the upper limit p-type dopant that can maintain high efficiency without being affected by free electron absorption. Determining the concentration is an indispensable issue in developing a laser element in the corresponding wavelength band.

  An object of the present invention is to solve these problems. In particular, the doping concentration of each p-type conductive semiconductor layer of a semiconductor laser element that oscillates in the near-infrared wavelength band of 1.0 μm or less is defined as an optical confinement factor. It is specified together with the product value of, and it achieves both low driving power and high reliability by balancing the various characteristics that are in a trade-off relationship with the doping concentration of improving efficiency and improving temperature characteristics / resistance values, etc. The wavelength band semiconductor laser device that maintains the characteristics and a method of manufacturing the same are provided. Furthermore, by mounting a semiconductor laser element having such advantages in the wavelength band as a light emitting element, a transmission device for high-speed optical wireless communication of a new standard that could not be realized in the past has been provided, and competition for higher speed has been achieved. The present invention provides an optical disk apparatus that enables high-speed reading and writing in the subsequent optical disk field.

が８．０×１０^１７ｃｍ^−３ 以下であり、
ドーピング濃度が１．０×１０ ^１８ ｃｍ ^−３ 以上であるｐ型導電型層の層厚の合計が、ｐ型導電型層全体の層厚の合計の８０％以上を占めており、
上記複数のｐ型導電型層は、上記活性層と上記ｐ型クラッド層との間に位置するｐ型光ガイド層を含んでおり、
上記ｐ型光ガイド層のドーピング濃度が２．０×１０ ^１７ ｃｍ ^−３ 以上であることを特徴としている。 The semiconductor laser device according to the first aspect of the present invention includes an n-type cladding layer, an active layer which is a quantum well active layer, and a plurality of p-type conductivity type layers m including a p-type cladding layer (here, in, m = 1,2 ... k, however, k is provided with a natural number) and,
The oscillation wavelength is 1.0 μm or less and 700 nm or more ,
The ratio of the amount of light present in the p-type conductivity type layer m to the total amount of light present in all the layers on the substrate is defined as an optical confinement coefficient Γ (m), and the doping concentration of the p-type conductivity type layer m is defined as P ( m) (cm ⁻³ ), the sum of products of Γ (m) and P (m)

Ri Der There 8.0 × ¹⁰ 17 ^{cm -3} or less,
The total thickness of the p-type conductivity layer having a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more occupies 80% or more of the total thickness of the p-type conductivity layer,
The plurality of p-type conductivity layers include a p-type light guide layer positioned between the active layer and the p-type cladding layer,
The p-type light guide layer has a doping concentration of 2.0 × 10 ¹⁷ cm ⁻³ or more .

  This semiconductor laser device has a partially deteriorated static characteristic due to the influence of free electron absorption in the near-infrared wavelength band of wavelength of 1.0 μm or less, where the influence of free electron absorption has been unclear. By avoiding current and efficiency degradation, the value of the drive current at the required light output can be reduced. Note that “efficiency” in this specification is one of the static characteristics of a semiconductor laser element, and is a drive necessary for obtaining an oscillation threshold current Ith (A) and a certain optical output Pop (W). If the current value is Iop (A), this is one of the basic static characteristics of the semiconductor laser element defined by Pop / (Iop-Ith).

  In order to determine the “upper limit value” of a p-type doping structure that can avoid free electron absorption in the near-infrared wavelength band with a wavelength of 1.0 μm or less, the present inventors actually perform a semiconductor laser element that oscillates at a wavelength of about 900 nm. Then, several types of devices having different combinations of the p-type doping concentration P and the optical confinement coefficient Γ of the same layer were manufactured, and the efficiency value and the internal absorption αi directly affecting the efficiency were calculated.

（以下、単にΣ｛Γ（ｍ）×Ｐ（ｍ）｝とも表す。）と、半導体レーザ素子の効率の値を決定する内部吸収αiとの間に図８のような関係があることがわかった。この結果では、内部吸収αiの値は、ｐ型導電型層ｍの光閉じ込め係数Γ（ｍ）と該ｐ型層ドーピング濃度Ｐ（ｍ）との積の総和Σ｛Γ（ｍ）×Ｐ（ｍ）｝の値が８．０×１０^１７ｃｍ^−３を越えると急激に増加している。半導体レーザ素子の内部吸収αiは自由電子吸収αｆｃとその他の吸収αoからなるが、その他の吸収αoの値は一般にドーピング濃度に依存せず、また通常４〜５ｃｍ^−１未満であり、半導体レーザ素子への影響が小さい。図８では、ｐ型ドーピング濃度に依存しないその他の吸収αoが３ｃｍ^−１程度あり、これにｐ型ドーピングに由来する自由電子吸収αｆｃが加わり、半導体レーザ素子の内部吸収αiとなることがわかる。これらのことから、ｐ型導電型層ｍの光閉じ込め係数Γ（ｍ）と該ｐ型層ドーピング濃度Ｐ（ｍ）との積の総和Σ｛Γ（ｍ）×Ｐ（ｍ）｝の値を８．０×１０^１７ｃｍ^−３以下の範囲に設定すれば、内部吸収αiのうち、ドーピング濃度に依存する自由電子吸収αｆｃの急激な増加を抑制できることがわかる。 As a result, the optical confinement coefficient Γ (m) of each p-type doping layer m (m = 1, 2,... K, where k is a natural number) and its doping concentration P (m) (cm ⁻³ , hereinafter omitted) Sum of products

(Hereinafter, it is also expressed simply as Σ {Γ (m) × P (m)}) and the internal absorption αi that determines the value of the efficiency of the semiconductor laser element is found to have a relationship as shown in FIG. It was. In this result, the value of the internal absorption αi is the sum Σ {Γ (m) × P () of the product of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m and the p-type layer doping concentration P (m). When the value of m)} exceeds 8.0 × 10 ¹⁷ cm ⁻³ , it rapidly increases. The internal absorption αi of the semiconductor laser element is composed of free electron absorption αfc and other absorption αo, but the value of the other absorption αo generally does not depend on the doping concentration and is usually less than 4 to 5 cm ^−1. The impact on is small. In FIG. 8, the other absorption αo that does not depend on the p-type doping concentration is about 3 cm ^−1, and the free electron absorption αfc derived from the p-type doping is added to the internal absorption αi of the semiconductor laser element. From these, the sum Σ {Γ (m) × P (m)} of the products of the optical confinement coefficient Γ (m) of the p-type conductivity type layer m and the p-type layer doping concentration P (m) is It can be seen that if the range is set to 8.0 × 10 ¹⁷ cm ⁻³ or less, the rapid increase in free electron absorption αfc depending on the doping concentration of the internal absorption αi can be suppressed.

Further, from FIG. 8, when the value of the sum Σ {Γ (m) × P (m)} is 6.0 × 10 ¹⁷ cm ⁻³ or less, the value of the internal absorption αi hardly changes. It can also be seen that a p-type doping layer structure of 6.0 × 10 ¹⁷ cm ⁻³ or less can almost eliminate the influence of free electron absorption αfc on internal absorption αi.

  These facts overturn the conventional recognition that there is no influence of free electron absorption in the near-infrared wavelength band of 1.0 μm or less. Depending on the structure even in this wavelength band, static characteristics due to free electron absorption, particularly efficiency. It was found that it could be affected by the deterioration of It was also found that good characteristics can be secured even at a relatively high p-type doping concentration that leads to an increase in free electron absorption by simultaneously considering the optical confinement factor of the p-type conductivity type layer in addition to the p-type doping concentration. As a result, the p-type doping concentration is higher than that of conventional semiconductor laser elements in the near-infrared wavelength band for the purpose of improving temperature characteristics and resistance values that are in a trade-off relationship with improving efficiency by suppressing free electron absorption. It became possible to set the value.

Note that the value of the internal absorption αi of the semiconductor laser element is preferably as small as possible. However, if it exceeds 10 cm ⁻¹ , the laser efficiency is significantly affected, and is necessary for high-speed wireless communication with an efficiency of 0.96 W / A or more. When the semiconductor laser device is mounted on such a transmitter for optical wireless communication, the internal absorption value is 10 cm ⁻¹ or less, more preferably 5 cm ⁻¹ or less. It is desirable.
In the short wavelength band, it is said that the influence of absorption due to the valley transition in the energy band of free electron absorption increases. This is a phenomenon that includes a component that is inversely proportional to the wavelength. In particular, the inventors have found that the value of free electron absorption αfc exceeds 10 cm ⁻¹ in a wavelength region of less than 700 nm . In the present invention, since the oscillation wavelength is set to be 700 nm or more, a highly efficient semiconductor laser device can be obtained without being affected by the free electron absorption component inversely proportional to the wavelength.

In the present invention , the total thickness of the p-type conductivity type layer having a p-type doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more accounts for 80% or more of the total thickness of the p-type conductivity type layer. Yes.

  Note that the p-type conductivity type layer defined here is a p-type conductivity type layer existing in a ridge and a portion connected to the top and bottom of the ridge when the semiconductor laser element is a ridge buried type, and only in the buried portion. The existing p-type conductivity layer is not included.

The operation of the above configuration is as follows. When the doping concentration of the main p-type conductivity type layer is set to a relatively low value of 10 ¹⁷ cm ⁻³ , undesirable effects on laser characteristics other than efficiency such as temperature characteristics, element resistance, and oscillation transverse mode appear. This effect is contrary to the case of free electron absorption. The lower the p-type doping concentration, the more adverse the semiconductor laser device. In order to investigate the effect of p-type doping on these three types of laser characteristics, a semiconductor laser device was fabricated in the corresponding wavelength band and the effect was confirmed. As a result, the p-type doping concentration was 80% or more of the entire p-type conductivity layer. It was found that this can be avoided by setting the thickness of the layer to 1 × 10 ¹⁸ cm ⁻³ or more. From the above, by setting the p-type doping concentration higher than the value in the conventional semiconductor laser device in the near-infrared wavelength band, the high temperature characteristics, which are in a trade-off relationship with the avoidance of free electron absorption, low A near-infrared semiconductor laser element having a wavelength of 1.0 μm or less that maintains power consumption and a stable oscillation transverse mode can be obtained.

  In one embodiment, the oscillation wavelength of the semiconductor laser element is 900 nm or less.

  In the region where the oscillation wavelength is 900 nm or less, the value of the index p of the wavelength λ in the above equation (1) representing the free electron absorption is small, so that the efficiency deterioration due to free electron absorption is more effective as shown in FIG. Can be avoided.

  In one embodiment, the light confinement structure confines light in a direction parallel to the active layer, and the sum of the light confinement coefficients of the layers on the side of the light confinement structure with respect to the active layer is The region in which light is confined in the light confinement structure is composed of at least one of the p-type conductivity layers.

  In this embodiment, in order to stabilize the light mode in the horizontal direction, that is, in the direction parallel to the active layer, the light confinement coefficient of the layer including the light confinement structure is made lower than that on the opposite side, particularly with the active layer interposed therebetween. ing. In general, when compared at the same doping concentration, the free electron absorption coefficient of the p-type dopant is larger than that of the n-type dopant, so that the free electron is better when the layer containing the optical confinement structure is p-type than the opposite case. Absorption effects are reduced, leading to improved efficiency values.

In one embodiment, the semiconductor laser device includes a current injection region and a non-current injection region, and has a current confinement structure that confines current in a direction parallel to the active layer, and the current injection region is the p-type conductive region. The doping concentration of the p-type conductivity type layer in the current injection region is 1.0 × 10 ¹⁸ cm ⁻³ or more.

In order to stabilize the oscillation transverse mode, the current injection region of the current confinement structure is generally set to a narrow width of about several μm, and the layer thickness occupies most of the p-type conductivity type layer. Therefore, the contribution to the element resistance of the p-type conductivity layer forming the current injection region is extremely large. Therefore, in this embodiment, by setting the doping concentration of these layers to be 1.0 × 10 ¹⁸ cm ⁻³ or more, more effectively avoiding deterioration of characteristics due to free electron absorption, It is also possible to reduce the resistance of the element.

  The semiconductor laser device of the present invention may include the optical confinement structure and the current confinement structure at the same time. In this case, the current injection region of the current confinement structure is generally formed to match the region where the light of the light confinement structure is confined.

  In one embodiment, the semiconductor laser element includes a current confinement structure that includes a current injection region and a non-current injection region and confines a current in a direction parallel to the active layer, and a part of the current confinement structure. Two boundary surfaces that define a region in which light is confined in the light confinement structure, and two boundary surfaces that define a current injection region in the current confinement structure. The distance between the two boundary surfaces is 2.2 μm or more at the portion closest to the active layer.

  The effect | action by this structure is as follows. In general, the distance between two horizontally separated boundary surfaces of the current confinement structure / light confinement structure, that is, the width of the current injection region (region where light is confined in the light confinement structure) of the current confinement structure (the ridge structure In this case, in a semiconductor laser device having a ridge width (several μm) and oscillating in a transverse fundamental mode, when the width is slightly changed, the near field pattern (NFP) diameter changes more rapidly than the change. Therefore, the narrower the width, the larger the NFP diameter with respect to the width, and the greater the light leakage to the layer in the non-current injection region of the current confinement structure. The layer in the non-current injection region is highly doped, and the leaked light is directly linked to an increase in free electron absorption in the layer in the non-current injection region according to the amount. On the other hand, in this embodiment, since the distance between the boundary surfaces, that is, the width of the current injection region is 2.2 μm or more, the NFP diameter is narrower than this width. Therefore, an increase in free electron absorption due to light leakage to the layer in the non-current injection region can be suppressed.

In the present invention, a doping concentration of a layer closest to the active layer among the p-type conductivity layers, that is, the p-type light guide layer is 2.0 × 10 ¹⁷ cm ⁻³ or more.

A semiconductor laser element in the near-infrared wavelength band of 1.0 μm or less has a smaller carrier-side energy gap ΔEc between the well layer and the barrier layer in the active layer than in the long-wavelength semiconductor laser element, so that carrier leakage from the active layer occurs. easy. However, in this embodiment, by setting the doping concentration of the p-type conductivity type layer closest to the active layer, that is, the p-type light guide layer to 2.0 × 10 ¹⁷ cm ⁻³ or more, carrier leakage from the active layer It can sufficiently fulfill its role as a barrier layer against high temperature characteristics. Note that the p-type conductivity layer closest to the active layer is a p-type conductivity layer to which a p-type dopant is intentionally added. An originally undoped layer is an adjacent p-type conductivity layer. Excludes layers that have become p-type conductivity layers as a result of diffusion of dopants.

In one embodiment, the upper Symbol p-type optical guide layer comprises two or more layers having different doping concentrations in the stacking direction, of the two or more layers of p-type optical guide layer, the doping of the layer closest to the active layer The concentration is lower than the doping concentration of the other p-type light guide layers.

  In this embodiment, free electron absorption can be avoided and temperature characteristics can be improved extremely effectively. For example, p-type doping concentration in the active layer near the side of the light guide layer P1, a p-type doping concentration of the light guide layer on the far side and P2, .GAMMA.1 light confinement coefficient near the side of the light guide layer, farther light When the optical confinement factor of the guide layer is Γ2, since the optical confinement factor of the gallium id layer on the side closer to the active layer is generally larger than the value on the far side (Γ1> Γ2), it is active as in this embodiment. By setting the doping concentration of the light guide layer closer to the layer to be smaller than the value of the light guide layer farther (P1 <P2), the p-type conductivity layer m, which is a parameter constituting the present invention, is set. Of the value of the sum Σ {Γ (m) × P (m)} of the product of the optical confinement coefficient Γ (m) and the p-type layer doping concentration P (m), the portion (Γ1 × P1 + Γ2 × Smaller than when P2) is set in reverse (P1> P2) Can Kusuru. Therefore, if the other p-type conductivity layers have the same layer structure, the value of the sum Σ {Γ (m) × P (m)} can be further reduced, so that the influence of free electron absorption can be suppressed. Alternatively, when the value of the sum Σ {Γ (m) × P (m)} is set to be constant, it is possible to increase the freedom of setting the doping concentration and the optical confinement coefficient of other p-type conductivity layers.

  Further, since the doping concentration in the portion close to the active layer is lowered, the diffusion rate proportional to the doping concentration can be reduced, and the diffusion of the dopant into the active layer can be suppressed and a highly reliable semiconductor laser device can be obtained. .

In one embodiment, the doping concentration of p-type conductivity type layer optical confinement factor Γ becomes 1.0 × ^{10 -4} or 8.0 × 1 is ^{0 1} 8 ^{cm -3} or less.

In general, when a semiconductor is heavily doped, the refractive index of the layer increases. However, in the case of an AlGaAs-based material, this tendency becomes significant when the concentration exceeds 8.0 × 10 ¹⁸ cm ⁻³ , and the optical confinement coefficient Γ of the corresponding layer is set to a set value. Bigger than. In this case, even if the total sum Σ {Γ (m) × P (m)} is set to 8.0 × 10 ¹⁷ cm ⁻³ or less according to the present invention, a high doping concentration of 8.0 × 10 ¹⁸ cm ⁻³ or more is obtained. The effect of free electron absorption in the corresponding layer is large, and the effect of reducing the efficiency as intended cannot be obtained. In addition, the degree of freedom in design also decreases. This embodiment avoids such inconvenience.

In one embodiment, the p-type conductivity type layer includes a p-type cap layer located above the p-type cladding layer, and the optical confinement coefficient Γ of the cap layer is 5.0 × 10 ⁻⁵ or less. is there.

In general, the cap layer has a very high concentration of 10 ¹⁸ cm ⁻³ to 10 ²⁰ cm ⁻³ in order to make the ohmic resistance low, and if there is light in such a layer, a large amount of doping occurs. Suffers from absorption. In addition, since a semiconductor material having a small energy gap is used for the cap layer in order to reduce contact resistance, the cap layer has a higher refractive index than the surrounding layers and is transparent to the oscillation wavelength. It becomes. For this reason, if there is light exceeding 5.0 × 10 ⁻⁵ as the value of the optical confinement factor, the cap layer becomes a waveguide layer, causing interference with the original guided light passing through the active layer. Since this interference induces kinks in the current-light output characteristics, when used as a semiconductor laser device for communication, communication quality such as a code error rate is deteriorated. In the present embodiment, it is possible to obtain a semiconductor laser element that avoids these influences and can perform a communication operation with high efficiency and stability.

  A method of manufacturing a semiconductor laser device according to a second aspect of the present invention is a method of manufacturing a semiconductor laser device having any one of the above-described structures, and the active layer and its activity using a metal organic chemical vapor deposition method. The method is characterized in that a layer adjacent to the layer is grown, the growth temperature of the active layer is made lower than the growth temperature of the adjacent layer, and the growth is temporarily interrupted at the interface where the growth temperature changes.

  If continuous growth is performed without any interruption at the boundary surface where the growth temperature changes, an overshoot of the ambient temperature occurs immediately after the temperature changes. The doping amount is determined by the concentration of the dopant material gas, the material of the conductivity type layer to be doped, and the temperature at the time of growth.Therefore, in the layer grown at a temperature different from the initially set temperature due to the overshoot of the ambient temperature, Therefore, an element having a doping concentration of 5 cannot be obtained. In the present invention, since the method of temporarily stopping and restarting the growth at the temperature change interface is used, a p-type doping structure as set can be obtained without causing such overshoot, and high efficiency and high temperature can be obtained. A semiconductor laser device having both characteristics / low power consumption can be manufactured.

  A transmission apparatus for optical wireless communication according to the third aspect of the present invention is equipped with a semiconductor laser element having any one of the above-described configurations of the present invention.

  As described above, the semiconductor laser device of the present invention is a semiconductor laser that realizes high efficiency, high temperature characteristics, and low power consumption in consideration of the effect of free electron absorption in the near infrared wavelength of 1.0 μm or less. It is an element. By using a semiconductor laser element having such characteristics, it is possible to generate light with a wavelength of 1.0 μm or less, which will be required for future high-speed optical wireless communication, with low driving power / voltage. Can increase the degree of freedom. Further, since the life of the semiconductor laser element itself is extended, the reliability of the apparatus is improved.

  An optical disc apparatus according to the fourth aspect of the present invention is equipped with a semiconductor laser element having any one of the above-described configurations of the present invention.

  According to the present invention, since the mounted semiconductor laser device realizes high efficiency, high temperature characteristics, and low power consumption, the competition for higher output continues in the near infrared wavelength band of 1.0 μm or less. In the optical disk apparatus, the disk rotation speed can be increased more than before. In particular CD-R / RW access time to the disk which has been a problem when writing to such is much shorter than the devices using conventional semiconductor laser device, to provide an optical disk apparatus which realizes a more comfortable operation be able to.

  According to the first aspect of the present invention, high concentration p-type doping can be performed while avoiding deterioration of static characteristics due to the influence of free electron absorption in the near-infrared wavelength band of 1.0 μm or less. In the wavelength band, it is possible to realize a semiconductor laser device that achieves both high efficiency, high temperature characteristics and low power consumption that are in a trade-off relationship with each other.

  In addition, according to the second aspect of the present invention, when manufacturing a semiconductor laser device having a p-type doping concentration set to a desired value, an overshoot of the atmospheric temperature during manufacturing that may occur in the metal organic chemical vapor deposition method is reduced. The semiconductor laser device can be manufactured so that the doping concentration of each conductive type layer that varies according to the temperature during growth can be set to a value as set, achieving both high efficiency and high temperature characteristics / low power consumption. The manufactured semiconductor laser device can be actually manufactured.

  Further, according to the third aspect of the present invention, the reliability of the optical wireless communication apparatus using a wavelength in the near infrared wavelength band of 1.0 μm or less can be improved, and the degree of freedom in designing the laser driver. Can also be raised.

  According to the fourth aspect of the present invention, in the optical disc apparatus, the number of revolutions of the disc can be increased more than before, and the data read / write speed can be increased.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. 1 and 2 are schematic cross-sectional views showing the structure and manufacturing method of this embodiment, respectively. First, the structure of this embodiment will be described with reference to FIG. In all the subsequent embodiments, the n-type conductivity type layer is represented by “n−”, and the p-type conductivity type layer is represented by “p−”. In addition, “lower” and “upper” in the names of layers mean that they are located on the “substrate side” and “the opposite side of the substrate”, respectively, across the active layer.

  The layer structure consists of a buffer layer 102, a lower cladding layer 103, a lower light guide layer 104, a multiple quantum well active layer 105 composed of a quantum well layer and a barrier layer, an upper light guide layer 106, and an upper first cladding layer on a substrate 101. 107, the etching stop layer 108, second upper cladding layer 109, a first cap layer 110 are stacked from the substrate side in this order, the bottom etch stop layer of the ridge in the second upper cladding layer 109 and the first cap layer 110 A ridge stripe structure (ridge stripe portion R) directly above is formed. Further, on both sides of the ridge stripe portion R, a first buried layer 111, a second buried layer 112, and a third buried layer 113 (collectively referred to as a buried portion F) are stacked so as to bury their side surfaces. The buried portion F and the ridge stripe portion R form a current confinement structure in which a current flows mainly directly below the ridge stripe portion R. Further, a second cap layer 114 and a third cap layer 115 are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

In a specific example of the first embodiment, an n-GaAs buffer layer 102 (0.5 μm thickness), an n-Al _0.452 Ga _0.548 As lower cladding layer 103 (1.8 μm) are formed on an n-GaAs substrate 101. N-Al _0.4 Ga _0.6 As lower light guide layer 104 (95 nm thickness), two 0.08% compressive strain In _0.06 Ga _0.94 As quantum well layer (4.5 nm thickness), n-Al _0.4 Ga _0.6 As ) And three layers of unstrained Al _0.15 Ga _0.85 As barrier layers (the thickness of the first and third barrier layers from the substrate side is 21.5 nm, the second is 8 nm thick from the three layers) Alternately stacked undoped multiple quantum well active layers 105 (oscillation wavelength 0.87 μm), p-Al _0.4 Ga _0.6 As upper light guide layer 106 (90 nm thickness), p-Al _0.5 Ga _0.5 As upper first cladding layer 107 (0.15 μm thick), p-GaAs etching stop layer 108 (4 m thick) p-Al _0.53 Ga _0.47 As second upper cladding layer 109 (1.28 thick), p-GaAs first cap layer 110 (0.75 .mu.m thick) are laminated from the substrate side in this order, The upper second cladding layer 109 and the first cap layer 110 form a ridge stripe portion R in which the lowermost portion of the ridge is directly above the etching stop layer.

  The ridge stripe portion R has a height of about 2 μm, and a width (that is, a distance between two boundary surfaces defining the ridge stripe portion R) is about 3.1 μm at the widest point immediately above the etching stop layer 108. Here, the height of the ridge stripe portion R means the sum of the layer thicknesses of the upper second cladding layer 109 and the first cap layer 110, which are removed by using an etching method described later.

Further, the n-Al _0.7 Ga _0.3 As first buried layer 111 (0.6 μm thickness) and the n-GaAs second buried layer 112 (0. 7 μm thick) and a p-GaAs third buried layer 113 (0.7 μm thick) are stacked, and the buried portion F and the ridge stripe portion R form a current confinement structure in which current flows mainly directly under the ridge stripe portion R. There is no. Further, a p-GaAs second cap layer 114 (0.95 μm thickness) and a p-GaAs third cap layer 115 (0.3 μm thickness) are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

  Next, the manufacturing method of this embodiment is demonstrated using FIG. 2A-2C. The constituent materials and layer thickness of the layers are shown above and are omitted here.

  First, as shown in FIG. 2A, a quantum consisting of an n-buffer layer 102, an n-lower cladding layer 103, an n-lower light guide layer 104, two well layers, and three barrier layers on an n-substrate 101. The well active layer 105, the p-upper light guide layer 106, the p-upper first cladding layer 107, the p-etching stop layer 108, the p-upper second cladding layer 109, and the p-first cap layer 110 are treated with an organic metal chemistry. The layers are stacked in this order using a phase growth method (MOCVD method). The growth temperature was 690 ° C. for the quantum well active layer and 713 ° C. for the other layers. At the boundary between the two temperatures, the growth was temporarily stopped, the temperature was changed, and the growth was performed again.

Thereafter, as shown in FIG. 2B, by using an etching method using the insulating film 121 made of SiO ₂ as a mask as an example, the ridge stripe portion R has a height of about 2 μm and a width of about 3.1 μm at the bottom. Is made. Etching is performed up to just above the p-GaAs etching stop layer 108 using a mixed aqueous solution of sulfuric acid and hydrogen peroxide and hydrofluoric acid.

  Next, as shown in FIG. 2C, by using the MOCVD method again, the n-first buried layer 111, the n-second buried layer 112, and the p-third are buried in the side surfaces on both sides of the ridge stripe portion R. The buried layer 113 is sequentially stacked. At this time, since the insulating film 121 is present on the upper surface of the ridge stripe portion R, the buried layers do not grow on the ridge stripe portion R, and the buried layers 111 to 113 are stacked only on both sides of the ridge stripe portion R. can do. Thereafter, the insulating film 121 is removed, and the p-second cap layer 114 and the p-third cap layer 115 are laminated again using the MOCVD method.

  After that, ohmic electrodes made of Ti / Pt / Au and AuGe / Ni are deposited on both the p-side and n-side surfaces as an example, and then the normal wafer process (wafer bar splitting, end face coating by cleavage) Through a reflective film formation and chip division by the method, a buried ridge type semiconductor laser element having a resonator length of 500 μm that emits light in the stripe direction is obtained. In this embodiment, silicon Si is used for the n-type and zinc Zn is used for the p-type as the dopant impurity material.

  In the present embodiment, a current flows from the upper side of FIG. 1 is a third cap layer side to downward in FIG. 1 is a substrate, but this time a structure such as the conductivity type of each layer described above Therefore, the first, second, and third buried layers 111, 112, and 113 serve as non-current injection regions, and current flows from the third cap layer 115 through the ridge stripe portion R that is the current injection region to the active layer 105. A current confinement structure is formed that flows to a layer below the etching stop layer 108 including.

  In addition, the light confinement structure for confining light in the direction parallel to the active layer in the present embodiment includes the upper second cladding layer 109 which is one of the layers constituting the ridge stripe portion R and the non-current injection region. It is formed by the difference in refractive index from the first buried layer 111 which is one of the layers to be formed. That is, the optical confinement structure shares these layers 109 and 111 with the current confinement structure.

The values of the doping concentration P and the optical confinement coefficient Γ of the p-type conductivity type layer of the semiconductor laser device of this embodiment are 1.35 × 10 ¹⁸ cm ⁻³ and 0.167, respectively, in the upper light guide layer 106. The clad layer 107 is 1.35 × 10 ¹⁸ cm ⁻³ , 0.118, the upper second clad layer 109 is 2.4 × 10 ¹⁸ cm ⁻³ , 0.049, and the GaAs cap layer is the first cap layer 110. 3.0 × 10 ¹⁸ cm ⁻³ , 1.0 × 10 ⁻⁶ , the second cap layer 114 is 3.0 × 10 ¹⁸ cm ⁻³ , less than 1.0 × 10 ⁻⁷ , and the third cap layer 115 is The p-type conductivity type is 1.0 × 10 ²⁰ cm ⁻³ and less than 1.0 × 10 ^−7, and extends from the upper light guide layer 106 adjacent to the active layer 105 to the third cap layer 115 through the ridge stripe portion R. Layer m (in this embodiment , M = 1,2 ... 7) of the optical confinement factor gamma (m) and the doping concentration P (sum of products of m) Σ {Γ (m) × P (m)} the value of approximately 5.02 × ^{10 17} It is set to be cm ⁻³ . Here, the optical confinement coefficient Γ (m) of the p-type conductivity type layer m is the ratio of the amount of light present in the layer m to the total amount of light present in all layers on the substrate, as described above. To tell.

  It should be noted that the p-etching stop layer 108 has an extremely small thickness compared to other p-type conductivity layers, and therefore the amount of light, more specifically, the light confinement factor, affects the total value. Since it is not negligible, it is excluded from consideration. In the embodiments described below, the p-etching stop layer is similarly handled.

In addition, the doping concentration of the buried layer serving as the non-current injection portion in the current confinement structure is 2.0 × 10 ¹⁸ cm ^{−3 for} the n−first buried layer 111 and 3.0 × for the n−second buried layer 112. 10 ¹⁸ cm ⁻³ , and the p-third buried layer 113 was 2.0 × 10 ¹⁸ cm ⁻³ .

As the characteristics of the semiconductor laser device of this embodiment, an efficiency value of 0.99 W / A and an internal absorption αi value of 4.0 cm ⁻¹ were obtained. Further, the temperature characteristics were as good as 120 K or more, and the resistance value did not increase due to the decrease in the p-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode.

As described above, in the present embodiment, in the semiconductor laser element that oscillates in the near-infrared wavelength band of wavelength 870 nm or less, the optical confinement coefficient Γ (m) and the doping concentration of the p-type conductivity type layer m. P sum of the products of (m) sigma values of {Γ (m) × P ( m)} of ^{5.02 × 10 17 cm -3, 8.0} × 10 17 cm -3 to set with the following values Thus, it was possible to avoid deterioration of static characteristics due to the influence of free electron absorption in the corresponding wavelength band, and to obtain a high value of 0.99 W / A efficiency.

Further, the sum of the products of the p-type doping concentration and the optical confinement coefficient is determined, and at the same time, the doping concentration of the p-type conductivity layer is 80% or more of the p-type conductivity type layer among all the p-type conductivity type layers. It is set to be 0 × 10 ¹⁸ cm ⁻³ . Specifically, the layer thickness and the doping concentration are respectively 90 nm and 1.35 × 10 ¹⁸ cm ^{−3 for} the upper light guide layer 106, and 0.15 μm and 1.35 × 10 ¹⁸ cm ^{− for the} upper first cladding layer 107. ³ , 4 nm for the etching stop layer 108, 8.2 × 10 ¹⁷ cm ⁻³ , 1.28 μm for the upper second cladding layer 109, 2.4 × 10 ¹⁸ cm ⁻³ , 0.75 μm for the first cap layer 110, 3.0 × 10 ¹⁸ cm ⁻³ , 0.95 μm for the second cap layer 114, 3.0 × 10 ¹⁸ cm ⁻³ , 0.3 μm for the third cap layer 115, 1.0 × 10 ²⁰ cm ⁻³ Of these p-type conductivity type layers, a layer having a thickness substantially equivalent to 100% is set to have a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ .

As described in the section of the prior art, when the doping concentration of the main p-type conductivity type layer is set to a relatively low value of 10 ¹⁷ cm ⁻³ , other than efficiency such as temperature characteristics, element resistance, and oscillation transverse mode. Undesirable effects appear on the laser characteristics. Contrary to the case of free electron absorption, this effect has an adverse effect on the laser characteristics as the p-type doping concentration is lower. Based on this fact, semiconductor laser elements in the near-infrared wavelength band were actually fabricated, and their laser characteristics were examined. As a result, it was found that a layer having a thickness of 80% or more with respect to the total thickness of the p-type conductivity type layer It was found that this effect can be avoided by setting the type doping concentration to 1 × 10 ¹⁸ cm ⁻³ or more. In this embodiment, the p-type conductivity layer doping concentration and layer thickness are determined so as to meet this condition, so that deterioration of static characteristics due to the influence of free electron absorption is avoided in the corresponding wavelength band, and temperature characteristics of 120K or higher. Etc., and other characteristics were able to ensure good values. A semiconductor laser device having both high efficiency and high temperature characteristics / low power consumption can be obtained.

  In this embodiment, since the conductivity type of the ridge stripe portion R (the upper second cladding layer 109 and the first cap layer 110) forming the optical confinement structure is p-type, it is free compared with the case where it is n-type. A semiconductor laser element capable of suppressing electron absorption and oscillating with higher efficiency could be obtained. In the semiconductor laser device of this embodiment, in order to stabilize the oscillation transverse mode in the direction parallel to the active layer, a material having a small energy gap is used for the ridge stripe portion, and the optical confinement coefficient of the layer above the etching stop layer 108 is used. Is low. As a result, the optical confinement factor of the n-type conductivity type layer below the active layer 105 is larger than that of the p-type conductivity layer that is equidistant from the active layer 105. In general, when compared at the same doping concentration, the free electron absorption coefficient of the p-type dopant is larger than the value of the n-type dopant, so that the p-type layer on the side containing the optical confinement structure is more free electron than the reverse case. Absorption effects can be reduced, leading to improved efficiency.

Furthermore, in the present embodiment, the doping concentrations of the upper second cladding layer 109 and the first to third cap layers 110, 114, and 115 are 2.4 × 10 ¹⁸ cm ⁻³ , 3.0 × 10 ¹⁸ cm ⁻³ , respectively. 3.0 × 10 ¹⁸ cm ⁻³ and 1.0 × 10 ²⁰ cm ⁻³ are all set to be 1.0 × 10 ¹⁸ cm ⁻³ or more. These layers constitute a current injection region whose width is determined by a narrow ridge width of several μm in the current confinement structure, and the total thickness is 3.28 μm, which is about 90 of the entire p-type conductivity type layer. %, The contribution of these layers to the device resistance is extremely large. For this reason, by setting the doping concentration of these layers to be 1.0 × 10 ¹⁸ cm ⁻³ or more, it is possible to avoid deterioration of characteristics due to free electron absorption and to reduce the resistance of the element. did it.

In the present embodiment, the optical confinement coefficients of the first to third cap layers 110, 114, and 115 are set to a very small value of about 5.0 × 10 ⁻⁶ . In general, the cap layer is doped at a very high concentration of 1.0 × 10 ¹⁸ cm ^{−3 to} 1.0 × 10 ²⁰ cm ⁻³ in order to obtain a low ohmic resistance. Suffers from absorption. Further, a semiconductor material having a small energy gap is used for the cap layer in order to reduce contact resistance. In this embodiment, GaAs is used. In this case, the refractive index is higher than that of the surrounding layers, and the layer is transparent to the oscillation wavelength. For this reason, when light having an optical confinement coefficient exceeding 5.0 × 10 ⁻⁵ exists, this cap layer becomes a waveguide layer, and causes interference with the original guided light passing through the active layer. Since this interference causes a plurality of kinks in the current-light output characteristics, communication quality such as a code error rate is deteriorated. In this embodiment, since the optical confinement coefficient of the cap layer is set to be about 5.0 × 10 ⁻⁶ and 5.0 × 10 ⁻⁵ or less, the communication operation can be performed efficiently and stably without being affected by these. A semiconductor laser device that can be obtained was obtained.

  Furthermore, in this embodiment, the ridge width (referred to as the width at the bottom of the ridge) that defines the width in the direction parallel to the active layer of the optical confinement structure and the current confinement structure is set to a value of 2.2 μm or more. The free electron absorption in the buried layers 111 to 113 could be suppressed. When the change of the near field pattern (NFP) diameter with respect to the ridge width of the semiconductor laser device that oscillates in the transverse fundamental mode with a ridge width of several μm was examined, the result indicated by the solid line in FIG. 3 was obtained. In FIG. 3, a broken line is a line when the NFP diameters shown for comparison are equal. From this figure, it can be seen that if the change in the ridge width is 1, the change in the NFP diameter is as small as about 0.11. For this reason, the narrower the ridge width, the larger the NFP diameter with respect to the ridge width. As a result, light leakage to the buried layers 111 to 113 increases. Since the buried layers 111 to 113 are doped at a high concentration so as to be a non-current injection portion, light leaked to the buried layers 111 to 113 is directly connected to an increase in free electron absorption corresponding to the amount. However, when the ridge width is 2.2 μm or more, the NFP diameter becomes narrower than the ridge width as shown in FIG. 3, so that increase of free electron absorption due to light leakage to the buried layer can be suppressed.

  However, when the ridge width is equal to or greater than 4.0 .mu.m, in many cases to destabilize the transverse mode beyond the so-called higher-order transverse cut-off frequency, and by even spectral hole burning even able to maintain the fundamental mode, kink Cause the occurrence of In this embodiment, since the ridge width is set to be narrower than 4.0 μm, it is possible to obtain a semiconductor laser device that stably oscillates in the transverse fundamental mode.

  By the way, in the present embodiment, in fabricating a semiconductor laser device having such a structure by using a metal organic chemical vapor deposition method, in particular, from the lower light guide layer 104 to the quantum well active layer 105 and further to the quantum well active layer 105. When the upper light guide layer 106 is grown from above, the gas flow is temporarily interrupted at the temperature discontinuous interface between the quantum well active layer growth temperature of 690 ° C. and the growth temperature of the layers other than the active layer 713 ° C. It uses a growth method that resumes after having started. If it grows continuously without interruption at this interface, a temperature overshoot occurs immediately after the temperature changes. Since the doping amount is determined by the concentration of the dopant material gas, the material of the doped conductive type layer, and the temperature during growth, the doping concentration of the layer grown at a temperature different from the temperature set by the temperature overshoot is actually Is different from the setting. In the present embodiment, since using a method that resumed once interrupted growth in the corresponding interface, it does not occur such an overshoot, in each conductive layer, it is possible to obtain a doping profile as designed, high efficiency And a semiconductor laser device having both high temperature characteristics / low power consumption.

  For the definition of the strain of the well / barrier layer constituting the quantum well active layer 105, the lattice constant of the GaAs substrate is a (GaAs) and the lattice constant of the well layer or barrier layer is a. )} / A (GaAs), where the sign is positive is compression strain, and negative is tensile strain. The magnitude of strain is expressed as an absolute value for both compression / tensile strain.

Second Embodiment
The structure of the semiconductor laser device according to the second embodiment of the present invention will be described with reference to FIG.

  The layer structure consists of a buffer layer 202, a lower first cladding layer 203a, a lower second cladding layer 203b, a lower light guide layer 204, a multiple quantum well active layer 205 composed of a quantum well layer and a barrier layer, an upper light, on a substrate 201. The guide layer 206, the upper first cladding layer 207, the etching stop layer 208, the upper second cladding layer 209, and the first cap layer 210 are laminated in this order from the substrate side, and the upper second cladding layer 209, the first cap layer 210, Thus, a ridge stripe structure (ridge stripe portion R) is formed in which the lowermost portion of the ridge is directly above the etching stop layer. On both sides of the ridge stripe portion R, a first buried layer 211, a second buried layer 212, and a third buried layer 213 (collectively a buried portion F) are stacked so as to bury their side surfaces. The stripe portion R forms a current confinement structure in which current flows mainly directly under the ridge stripe portion R. Further, a second cap layer 214 and a third cap layer 215 are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F. Reference numerals 216 and 217 denote a p-type electrode and an n-type electrode, respectively.

In a specific example of the second embodiment, an n-GaAs buffer layer 202 (0.5 μm thick), an n-Al _0.45 Ga _0.55 As lower first cladding layer 203a (3 0.04 μm thick), n-Al _0.47 Ga _0.53 As lower second cladding layer 203b (0.24 μm thick), n-Al _0.43 Ga _0.57 As lower light guide layer 204 (103 nm thick), Two layers of 0.4% compressive strain In _0.21 Ga _0.79 As _0.62 P _0.38 quantum well layer (7.5 nm thickness) and three layers 0.8% tensile strain In _0.09 Ga _{0 .91} As _0.4 P _0.6 Barrier Layer (Undoped Multiple Quantum Well with Alternating Layers of Layers 10th and 5th Thickness of First and Third Barrier Layers from the Substrate Side of the Three Layers) Active layer 205 (oscillation wavelength 0.75 μm), p-Al _0.43 Ga _0.57 As upper light guide layer 206 (53 nm thickness), p-Al _0.49 Ga _0.51 As upper first cladding layer 207 (0.177 μm thickness), p-GaAs etching stop layer 208 (3 nm thickness), p-Al _0.49 Ga 0.5 _{. A 51} As upper second cladding layer 209 (1.28 μm thickness) and a p-GaAs first cap layer 210 (0.75 μm thickness) are laminated in this order from the substrate side, and the upper second cladding layer 209 and the first cap layer 210 are laminated. Thus, a ridge stripe portion R is formed in which the lowermost portion of the ridge is directly above the etching stop layer. The ridge stripe portion R has a height of about 2 μm and a width of about 2.8 μm at the widest portion immediately above the etching stop layer 208.

The n-Al _0.7 Ga _0.3 As first buried layer 211 (0.6 μm thickness) and the n-GaAs second buried layer 212 (0.7 μm thickness) are embedded on both sides of the ridge stripe portion R. ), A p-GaAs third buried layer 213 (0.7 μm thick) is stacked, and the buried portion F and the ridge stripe portion R form a current confinement structure in which current flows mainly directly below the ridge stripe portion R. . Further, a p-GaAs second cap layer 214 (0.95 μm thickness) and a p-GaAs third cap layer 215 (0.3 μm thickness) are laminated on the entire upper surface of the ridge stripe portion R and the buried portion F.

  The growth profile such as the growth temperature and interruption when the semiconductor laser device of this embodiment is manufactured using the metal organic chemical vapor deposition method is the same as that of the first embodiment. The process up to the edge emitting semiconductor laser element is also the same as in the first embodiment.

In the semiconductor laser device of this embodiment, the p-type conductivity layer doping concentration P and the optical confinement coefficient Γ are 2.0 × 10 ¹⁸ cm ⁻³ and 0.086 for the upper light guide layer 206, respectively. 2.0 × 10 ¹⁸ cm ⁻³ , 0.146 for one cladding layer 207, 5.0 × 10 ¹⁸ cm ⁻³ , 0.062 for the upper second cladding layer 209, and the first cap layer for the GaAs cap layer 210 is 3.0 × 10 ¹⁸ cm ⁻³ , 5.0 × 10 ⁻⁶ , and the second cap layer 214 is 3.0 × 10 ¹⁸ cm ⁻³ , less than 1.0 × 10 ⁻⁷ , and the third cap layer 215. P-type conductivity from the upper light guide layer 206 adjacent to the active layer 205 to the third cap layer 215 through the ridge stripe portion R, and less than 1.0 × 10 ²⁰ cm ⁻³ and 1.0 × 10 ^−7. Mold layer m (in this embodiment m = 1,2 ... 7) of the optical confinement factor gamma (m) and the doping concentration P (sum of products of m) Σ {Γ (m) × P (m)} value substantially 7.77 × ¹⁰ 17 cm of ^-3 .

In addition, the doping concentration of the buried layer serving as a non-current injection portion in the current confinement structure is 3.0 × 10 ¹⁸ cm ^{−3 for} the n−first buried layer 211 and 3.0 × 10 10 for the n−second buried layer 212. ¹⁸ cm ⁻³ , and the p-third buried layer 213 was 5.0 × 10 ¹⁸ cm ⁻³ .

As the characteristics of the semiconductor laser device of this embodiment, 0.97 W / A in terms of efficiency and 5 cm ^{−1 in} terms of internal absorption αi were obtained. Further, the temperature characteristics were as good as 120 K or more, and the resistance value did not increase due to the decrease in the p-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode.

  As described above, in this embodiment as well, as in the first embodiment, it is possible to achieve both high efficiency and high temperature characteristics / low power consumption without being affected by free electron absorption. A semiconductor laser element that oscillates in the infrared wavelength band was obtained. In the second embodiment, the values of the optical confinement coefficient and the doping concentration of each individual layer of the p-type conductivity type are values that should satisfy both high efficiency and high temperature characteristics / low power consumption as in the first embodiment. The range is set.

Further, in the present embodiment, the present invention is applied to a semiconductor laser element that oscillates at a wavelength shorter than that of the first embodiment, in particular, an oscillation wavelength of 750 nm. As described above, in the short wavelength band, it is said that the influence of absorption due to transition between valleys in the energy band in the free electron absorption becomes large. This has a component inversely proportional to the wavelength, but the present inventors have found that the value of free electron absorption αfc exceeds 10 cm ⁻¹ particularly at a wavelength of 700 nm or less. Based on this, since the laser oscillation wavelength is set to 750 nm in this embodiment, the semiconductor laser device has a relatively high efficiency of 0.97 W / A without being affected by absorption by a free electron absorption component inversely proportional to the above-described wavelength. Could get.

Further, in the present embodiment, as in the first embodiment, the optical confinement coefficients of the first to third cap layers 210, 214, and 215 are about 1.0 × 10 ⁻⁵ and 1.0 × 10 ^−5. The light confinement coefficient of the p-type conductivity type all layers from the upper light guide layer 206 through the ridge stripe portion R to the third cap layer 215 is set to 1.0 × 10 ^−4. a doping concentration of more layers, the upper optical guide layer at 2.0 × ¹⁰ 18 ^{cm -3,} an upper first cladding layer at 2.0 × ¹⁰ 18 ^{cm -3,} second upper cladding layer at 5.0 × 10 ¹⁸ cm ⁻³ and all are set to 8.0 × 10 ¹⁸ cm ⁻³ or less. In general, when a semiconductor is heavily doped, the refractive index of the layer increases. However, when the doping concentration exceeds 8.0 × 10 ¹⁸ cm ⁻³ in an AlGaAs-based material, this tendency becomes significant. The confinement factor Γ becomes larger than the set value. For this reason, the sum Σ of the product of the optical confinement coefficient and the doping concentration increases, and the efficiency decreases. However, since the amount of light existing in a layer having an optical confinement factor smaller than 1.0 × 10 ⁻⁴ is extremely small, even if the refractive index of the corresponding layer is increased, the light shape of the entire laser device is not changed. Absent. In the present embodiment, the upper limit of the doping concentration of a layer having an optical confinement coefficient of 1.0 × 10 ⁻⁴ or more among all p-type conductivity type layers is 5.0 × 10 ¹⁸ cm ⁻³ , and 8.0 × 10. ^Since it was set to be ¹⁸ cm ⁻³ or less, the set light distribution shape could be maintained, and a semiconductor laser device having both high efficiency as intended and high temperature characteristics / low power consumption was obtained.

<Third Embodiment>
The structure of the semiconductor laser device according to the third embodiment of the present invention will be described with reference to FIG.

  The layer structure includes a buffer layer 302, a lower first cladding layer 303a, a lower second cladding layer 303b, a lower light guide layer 304, a multiple quantum well active layer 305 composed of a quantum well layer and a barrier layer, and an upper portion. The first light guide layer 306a, the upper second light guide layer 306b, the upper first cladding layer 307, the etching stop layer 308, the upper second cladding layer 309, the first cap layer 310, and the second cap layer 311 are arranged in this order on the substrate side. The upper second cladding layer 309 and the first and second cap layers 310 and 311 form a ridge stripe structure (ridge stripe portion R) in which the lowermost portion of the ridge is directly above the etching stop layer 308. An insulating film 322 is laminated on the side surface and both sides of the ridge stripe portion R, and the insulating film 322 and the ridge stripe portion R form a current confinement structure in which current flows only directly under the ridge stripe portion.

In a specific example of the third embodiment, an n-GaAs buffer layer 302 (0.5 μm thick), an n-Al _0.56 Ga _0.44 As lower first cladding layer 303 a (2 μm) are formed on an n-GaAs substrate 301. Thickness), n-Al _0.3 Ga _0.7 As lower second cladding layer 303b (0.05 μm thickness), n-Al _0.41 Ga _0.59 As lower light guide layer 304 (100 nm thickness), two layers 0.14% compression strain of In _0.12 Ga _0.88 As quantum well layer (4.8 nm thickness) and three unstrained Al _0.15 Ga _0.85 As barrier layers (from the substrate side of the three layers) Undoped multiple quantum well active layer 305 (oscillation wavelength 0.89 μm), p-Al _0.4 Ga 0,0, alternately stacked with a thickness of 22 nm for the first and third barrier layers and a thickness of 8 nm for the second barrier layer _{. 6} As the first light guide layer 306a (50 nm thick) top, p-Al _0.4 Ga _0.6 As upper second light Id layer 306 b (50 nm _{thick), p-Al 0.47 Ga 0.53} As first upper cladding layer 307 (0.4 .mu.m thick), p-InGaAsP etch stop layer 308 (15 nm thick), p-Al _0.5 Ga _0.5 As upper second cladding layer 309 (1.28 μm thickness), p-GaAs first cap layer 310 (1.7 μm thickness), p-GaAs second cap layer 311 (0.3 μm thickness) in this order. A ridge stripe structure (ridge stripe portion R) is formed by laminating from the substrate side, and the upper second cladding layer 309 and the first and second cap layers 310 and 311 have the bottom of the ridge directly above the etching stop layer 308. Yes.

The ridge stripe portion R has a height of about 3 μm and a width of about 2.5 μm at the widest portion immediately above the etching stop layer 308. A SiO ₂ film is laminated as an insulating film 322 on the side surface and both sides of the ridge stripe portion R to form a current confinement structure in which current flows only directly under the ridge stripe portion.

  A p-type electrode 316 is formed on the insulating film 322 and the second cap layer 311, and an n-type electrode 317 is formed on the back surface of the substrate 301.

  Whereas the semiconductor laser elements of the first and second embodiments are ridge buried semiconductor laser elements, the semiconductor laser element of this embodiment is a ridge waveguide semiconductor laser element.

  In the manufacturing process of the semiconductor laser device of this embodiment, after forming the ridge stripe portion R, the insulating film 322 is formed on the entire surface of the wafer, and then the insulating film portion on the second cap layer 322 is formed by using a photolithography technique. The current path is formed by removing. Except for this point, the manufacturing process of the semiconductor laser device of this embodiment is generally similar to the manufacturing process in the two previous embodiments, the growth during the growing crystals by metal-organic chemical vapor deposition Growth profiles such as temperature and interruption are the same as those in the first and second embodiments. Further, the process up to the end-emitting semiconductor laser element after electrode formation is the same as in the previous embodiment.

The values of the doping concentration P and the optical confinement coefficient Γ of the p-type conductivity type layer of the semiconductor laser device of this embodiment are 3.0 × 10 ¹⁷ cm ⁻³ and 0.135, respectively, in the upper first light guide layer 306a. 8 × 10 ¹⁷ cm ⁻³ , 0.06 for the second light guide layer 306 b, 1.35 × 10 ¹⁸ cm ⁻³ , 0.219 for the upper first cladding layer 307, 3.0 for the upper second cladding layer 309. For the × 10 ¹⁸ cm ⁻³ , 0.011 and GaAs cap layers, the p-first cap layer 310 is 5.0 × 10 ¹⁸ cm ⁻³ , 1.0 × 10 ⁻⁶ , p-second cap layer 311. ^Is less than 1.0 × 10 ²⁰ cm ⁻³ and less than 1.0 × 10 ^−7, and p from the upper first light guide layer 306a adjacent to the active layer 305 to the second cap layer 311 through the ridge stripe portion R Type conductivity type layer m (this implementation The state, m = 1,2 ... 7 optical confinement factor gamma (m) the product sum Σ {Γ (m) × P (m)} value 4.17 × 10 of the doping concentration P (m)) of It is set to be ¹⁷ cm ⁻³ .

The static characteristics of the semiconductor laser device of the present embodiment were 1.0 W / A in terms of efficiency and 3.5 cm ⁻¹ as the value of internal absorption αi. Further, the temperature characteristics were as good as 130 K or higher, and the resistance value did not increase due to the decrease of the p-type doping concentration. A linear current-light output characteristic was obtained without the occurrence of kinks due to instability of the transverse mode.

  Also in the present embodiment, a semiconductor laser device that oscillates in the near-infrared wavelength band of wavelength of 1.0 μm or less, having both high efficiency and high temperature characteristics / low power consumption, without being affected by free electron absorption. I was able to.

Particularly in this embodiment, the sum Σ {Γ (m) × P (m)} of the product of the optical confinement coefficient and the doping concentration of each p-type conductivity type layer is set to be smaller than those in the first and second embodiments. FIG. 8 shows a graph showing the relationship between Σ {Γ (m) × P (m)} and the internal absorption αi. From this graph, it can be seen that, in particular, the total Σ {Γ (m) × P (m) } Is set to 6.0 × 10 ¹⁷ cm ⁻³ or less, it can be seen that deterioration of characteristics due to free electron absorption in the p-type conductivity layer can be almost completely prevented.

  In particular, in the semiconductor laser device of this embodiment, the oscillation wavelength is set so that the wavelength is 890 nm and does not exceed 900 nm. When the oscillation wavelength is 900 nm or less, the value of the index p of the wavelength λ is small in the above equation (1) for obtaining free electron absorption, so that deterioration of efficiency due to free electron absorption can be suppressed as shown in FIG. .

Further, in the present embodiment, as in the first and second embodiments, the sum of the products of the optical confinement coefficient and the doping concentration of each p-type conductivity type is defined, and the p-type conductivity adjacent to the undoped layer including the active layer is defined. The doping concentration of the mold layer was set to be 2.0 × 10 ¹⁷ cm ⁻³ or more. The semiconductor laser device of this embodiment has a smaller energy gap ΔEc between the well layer and the barrier layer than the long wavelength band semiconductor laser device, and the doping concentration in the vicinity of the active layer is 2. When it is less than 0 × 10 ¹⁷ cm ⁻³ , carrier leakage from the undoped layer including the active layer increases rapidly, and the temperature characteristics of the semiconductor laser device deteriorate. In this embodiment, since the doping concentration in the immediate vicinity of the active layer is set to 3.0 × 10 ¹⁷ cm ⁻³ , it can sufficiently serve as a barrier layer against the carrier leak, and the first and second implementations of 130 K or more. A temperature characteristic equivalent to or better than that of the form could be secured.

In the present embodiment, the value of the sum Σ of the product of the optical confinement coefficient and the doping concentration of each p-type conductivity type layer is specified, and the p-type upper light guide layer is divided into two layers 306a and 306b in the layer stacking direction. In other words, the doping concentration of the upper first light guide layer 306a, which is the layer closer to the active layer, that is, the layer having the larger optical confinement coefficient, is 3.0 × 10 ¹⁷ cm ^−3, and the p-type upper second light guide on the far side The value of the layer 306b is set to be smaller than 8.0 × 10 ¹⁷ cm ⁻³ . This has made it possible to more effectively suppress free electron absorption and improve temperature characteristics. At the same time, the diffusion of dopant into the active layer could be suppressed, and a highly reliable semiconductor laser device could be obtained.

  In the above three embodiments, semiconductor laser elements having wavelengths of about 750 nm and less than 900 nm have been described. However, the gist of the present invention is the near-infrared wavelength band having a wavelength of 1.0 μm or less, where free electron absorption has not been a problem in the past. To determine the extent of the effect of free electron absorption, and by defining the sum of the product of the doping concentration of the p-type conductivity layer in the current injection region and the optical confinement factor, the effect of free electron absorption in that wavelength band In the near-infrared wavelength band that oscillates at a wavelength of 1.0 μm or less, and preferably 700 nm or more, with a p-type conductivity layer. The present invention can be applied to all semiconductor laser elements.

  In all the embodiments described above, the p-type cladding layer is divided into two parts by the etching stop layer. However, according to the gist of the patent described above, it is defined by the mixed crystal ratio of the material constituting the layer. The classification of the cladding layer is not directly related to the essence of the present invention. For example, for a BH (buried hetero) structure type semiconductor laser element constituted by one clad layer without an etching stop layer, or a semiconductor laser element constituted by a plurality of layers of clad layers for other purposes. However, the contents of this patent can be applied.

  Further, in all the above embodiments, a GaAs substrate is used and the layer material of the doped layer is all AlGaAs-based material. However, in the case of a III-V group compound semiconductor, p-type doping concentration and optical confinement coefficient are Since the contribution of the sum of products to the free electron absorption αfc is almost the same, if the requirements constituting the present invention are satisfied, semiconductors composed of other III-V group compound semiconductor materials such as InGaP, InGaAlP, etc. The present invention can be applied to all laser elements.

  As for the conductivity type, the side closer to the substrate than the active layer is n-type and the side far from the active layer is p-type in all embodiments, but the conductivity type opposite to that of the above embodiment, that is, the side closer to the substrate than the active layer is p-type and far away. The present invention can also be applied to a configuration in which the side is n-type.

<Fourth embodiment>
An optical wireless communication transmission apparatus according to the fourth embodiment of the present invention will be described with reference to FIG. This is an apparatus for transmitting signal light to a receiving apparatus located in a spatially separated place using the semiconductor laser element 401 of the first embodiment.

  Specifically, a signal generation source 402, a transmission circuit 403, a laser driver 404, and a semiconductor laser element 401 that converts an electric signal into light and radiates it into the space are provided, and an electric signal emitted from the signal generation source 402 is transmitted. The electric signal is input to the laser driver 404 through the trust circuit 403, and this electric signal is E / O (electrical / optical) converted by using the semiconductor laser element 401 to be emitted light 405 to the external space. At this time, a resin mold for diffusing light so as to satisfy the safety standard for the human body, particularly the eyes, is provided outside the semiconductor laser element, and the light emitted from the semiconductor laser element 401 is made incoherent to the extent that the safety standard is satisfied. The external radiation light 405 is used.

  As described above, by using the semiconductor laser device with high efficiency and high temperature characteristics / low power consumption according to the first embodiment, a near infrared wavelength band of 1.0 μm or less required for future high-speed optical wireless communication is required. Since light can be generated with low drive power / voltage, there is a margin in power consumption of the laser driver and other circuit components, and the degree of freedom in designing the driver and circuit can be increased. In addition, since the drive current can be lowered due to high efficiency and high temperature characteristics, the life of the semiconductor laser element is extended and the reliability of the device is improved.

<Fifth Embodiment>
An optical disc recording / reproducing apparatus according to the fifth embodiment of the present invention will be described with reference to FIG. This is a device for writing data on the optical disc 501 and reproducing the written data. The light emitting element 502, collimating lens 503, beam splitter 504, λ / 4 polarizing plate 504, The light irradiation objective lens 506, the reproduction light objective lens 507, the signal light detection light receiving element 508, and the signal reproduction circuit 509 are provided. As the light emitting element 502, the semiconductor laser element according to the second embodiment of the present invention described above is used. The operation of this optical disk recording / reproducing apparatus will be described below.

  First, at the time of writing, the signal light emitted from the semiconductor laser element 502 is converted into parallel light by the collimate lens 503, passes through the beam splitter 504, and the polarization state is adjusted by the λ / 4 polarizing plate 505. The light is condensed by the objective lens 506 and irradiated onto the optical disc 501. On the other hand, at the time of reading, laser light without a data signal is irradiated onto the optical disc 501 along the same path as at the time of writing. The laser light is reflected by the surface of the optical disk 501 on which the data is recorded, passes through the laser light irradiation objective lens 506 and the λ / 4 wavelength plate 505, and then is reflected by the beam splitter 504. After changing the angle by 90 degrees, the light is condensed by the reproduction light objective lens 507 and incident on the signal detection light receiving element 508. In the signal detecting light receiving element 508, the recorded data signal is converted into an electric signal by the intensity of the incident laser beam, and the signal light reproducing circuit 509 reproduces the original signal.

  Since the optical disk apparatus of the present embodiment uses a semiconductor laser element that operates at a higher optical output than before, the data can be read and written even if the rotational speed of the disk is made higher than before. Accordingly, an optical disc apparatus that realizes a more comfortable operation because the access time to the disc, which has been a problem particularly when writing to a CD-R / RW, is much shorter than a conventional device using a semiconductor laser element. Could be provided.

1 is a schematic cross-sectional view showing a structure of a semiconductor laser device according to a first embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing a state where a substrate to a first cap layer are stacked in the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. It is typical sectional drawing showing the state which the etching process was complete | finished in the manufacture process of the semiconductor laser element of 1st Embodiment of this invention. FIG. 5 is a schematic cross-sectional view showing a state where a third cap layer is stacked in the manufacturing process of the semiconductor laser device according to the first embodiment of the present invention. It is a graph which shows the relationship between the ridge width | variety obtained by experiment, and the near field pattern (NFP) diameter of a semiconductor laser element. It is typical sectional drawing which shows the structure of the semiconductor laser element of 2nd Embodiment of this invention. It is typical sectional drawing which shows the structure of the semiconductor laser element of 3rd Embodiment of this invention. It is a block diagram which shows the structure of the apparatus for optical wireless communications of 4th Embodiment of this invention. It is a typical block diagram which shows the optical disk recording / reproducing apparatus of 5th Embodiment of this invention. It is the graph showing the relationship between the value of internal absorption (alpha) i of the semiconductor laser element obtained by experiment, and the sum total of the product of the doping concentration of a p-type semiconductor layer, and a light density. It is the schematic diagram which represented the relationship between free electron absorption and a wavelength by using doping concentration as a parameter.

101, 201, 301 Substrate 102, 202, 302 Buffer layer 103, 203a, 203b, 303a, 303b Lower cladding layer 104a, 104b, 204, 304a, 304b Lower light guide layer 105, 205, 305 Active layer 106, 206, 306a , 306b Upper light guide layer 107, 207, 307 Upper first cladding layer 108, 208, 308 Etching stop layer 109, 209, 309 Upper second cladding layer 110, 210, 310 First cap layer
114, 214, 311 Second cap layer 115, 215 Third cap layer 111, 211 First buried layer 112, 212 Second buried layer 113, 213 Third buried layer 116, 216, 316 P-type electrode 117, 217, 317 n-type electrode 121 insulating film for selective etching 322 insulating film for current confinement 401 semiconductor laser element of first embodiment 402 signal generation source 403 transmission circuit 404 laser driver 405 emitted light to external space 501 optical disc 502 of second embodiment Semiconductor laser element 503 Collimate lens 504 Beam splitter 505 λ / 4 polarizing plate 506 Laser light irradiation objective lens 507 Reproduction light objective lens 508 Signal light detection light receiving element 509 Signal reproduction circuit R Ridge stripe part F Embedding Part

Claims (11)

An n-type cladding layer, an active layer that is a quantum well active layer, and a plurality of p-type conductivity type layers m including a p-type cladding layer (where m = 1, 2,..., K, where k is with a natural number) and,
The oscillation wavelength is 1.0 μm or less and 700 nm or more ,
The ratio of the amount of light present in the p-type conductivity type layer m to the total amount of light present in all the layers on the substrate is defined as an optical confinement coefficient Γ (m), and the doping concentration of the p-type conductivity type layer m is defined as P ( m) (cm ⁻³ ), the sum of products of Γ (m) and P (m)

Ri Der There 8.0 × ¹⁰ 17 ^{cm -3} or less,
The total thickness of the p-type conductivity layer having a doping concentration of 1.0 × 10 ¹⁸ cm ⁻³ or more occupies 80% or more of the total thickness of the p-type conductivity layer,
The plurality of p-type conductivity layers include a p-type light guide layer positioned between the active layer and the p-type cladding layer,
A semiconductor laser device, wherein the p-type light guide layer has a doping concentration of 2.0 × 10 ¹⁷ cm ⁻³ or more .
  2. The semiconductor laser device according to claim 1, wherein the oscillation wavelength is 950 nm or less. Having a light confinement structure for confining light in a direction parallel to the active layer,
With respect to the active layer, the sum of the light confinement factors of the layer on the side having the light confinement structure is smaller than the sum of the light confinement factors of the layer on the side having no light confinement structure,
The semiconductor laser device according to claim 1 or 2 area among light is confined in the optical confinement structure is characterized by comprising at least one of the p-type conductivity type layer. A current confinement structure comprising a current injection region and a non-current injection region, and confining current in a direction parallel to the active layer,
The current injection region is made of at least one of the p-type conductivity type layers, and the doping concentration of the p-type conductivity type layer in the current injection region is 1.0 × 10 ¹⁸ cm ⁻³ or more. Item 4. The semiconductor laser device according to any one of Items 1 to 3 . A current confinement structure comprising a current injection region and a non-current injection region, and confining current in a direction parallel to the active layer;
It comprises a part of the current confinement structure, and comprises a light confinement structure that confines light in a direction parallel to the active layer,
Two boundary surfaces that define a region in which light is confined in the light confinement structure coincide with two boundary surfaces that define a current injection region in the current confinement structure, and a distance between the two boundary surfaces. the semiconductor laser device according to any one of claims 1 to 4, characterized in that at 2.2μm or more in the portion closest to the active layer. Upper Symbol p-type optical guide layer comprises two or more layers having different doping concentrations in the stacking direction, these two-layer or more p-type optical guide layer, the doping concentration of the layer closest to the active layer other p-type 6. The semiconductor laser device according to claim 1, wherein the concentration of the light guide layer is smaller than that of the light guide layer. Any of claims 1 to 6, wherein the doping concentration of p-type conductivity type layer optical confinement factor Γ becomes 1.0 × ^{10 -4} or more is 8.0 × ^{1 0} 1 8 ^{cm -3} or less The semiconductor laser device according to any one of the above. The p-type conductivity type layer includes a p-type cap layer located above the p-type cladding layer.
The semiconductor laser device according to any one of claims 1 to 7, wherein the optical confinement factor of the cap layer Γ is 5.0 × 10 ^-5 or less. A method of manufacturing a semiconductor laser device according to any one of claims 1-8,
The active layer and the layer adjacent to the active layer are grown using metalorganic chemical vapor deposition, the growth temperature of the active layer is lower than the growth temperature of the adjacent layer, and the growth temperature changes. A method of manufacturing a semiconductor laser device, wherein growth is temporarily interrupted at a boundary surface. A transmitter for optical wireless communication equipped with the semiconductor laser element according to any one of claims 1 to 8 . An optical disk device on which the semiconductor laser element according to any one of claims 1 to 8 is mounted.

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