JP3439168B2 - Semiconductor laser - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a nitride semiconductor laser.

[0002]

2. Description of the Related Art In recent years, research and development of nitride semiconductor lasers have been carried out as a recording or reproducing light source used in high density and large capacity optical disk systems.

Also in this nitride semiconductor laser,
In order to use it as a light source for an optical disk system, transverse mode control is required as with a semiconductor laser that emits infrared light or red light. We propose a refractive index waveguide type semiconductor laser suitable for this transverse mode control. Has been done.

In order to realize a refractive index guiding structure in a nitride semiconductor laser, a current blocking layer for confining a current flowing in an active layer is formed of, for example, a mixed crystal ratio of AlN (hereinafter referred to as Al composition). There are two possible methods: a real refractive index guide structure having a larger Al composition than that of the cladding layer, or a loss guide structure having a bandgap of the current blocking layer smaller than that of the active layer.

However, in order to construct a semiconductor laser having a loss guide structure, InGaN having a larger InN mixed crystal ratio (hereinafter referred to as In composition) than the active layer can sufficiently block current and sufficiently absorb light. When the current blocking layer is formed by growing it to the maximum thickness (for example, about 0.5 μm or more), the current blocking layer exceeds the critical film thickness, so that there is a problem that the crystallinity of the grown layer is significantly reduced.

Further, in order to form a real refractive index guide structure, AlGaN having a larger Al composition than the cladding layer can sufficiently block the current and sufficiently confine the light (for example, about 0.5 μm or more). Even when the current blocking layer is formed by growing the Al layer, the cladding layer containing Al and the current blocking layer become brittle, cracks occur, and the crystallinity of the grown layer is significantly reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned drawbacks of the conventional example. In the current blocking layer having a large Al composition, In composition, etc. It is an object of the present invention to provide a semiconductor laser that can be formed to a thickness that can sufficiently block the.

[0008]

A semiconductor laser according to the present invention is a semiconductor laser having an active layer made of a nitride-based semiconductor material, and a plurality of current blocking layers for confining a current flowing through the active layer. Is a superlattice structure consisting of

In the semiconductor laser having such a structure, the layer thickness of each layer of the superlattice structure forming the current blocking layer becomes small, so that the strain between the underlying layer such as the cladding layer and the current blocking layer is reduced. Is alleviated.

Further, in the semiconductor laser of the present invention, the current blocking layer is made of Al _X Ga _{1 -X} N (where 0 ≦ X ≦ 1), and the superlattice structure is made up of a plurality of layers having different X values. Is characterized in that.

In this case, even if the average Al composition in the entire current blocking layer is increased or the layer thickness of the current blocking layer is increased, the decrease in crystallinity of the current blocking layer can be suppressed. Therefore, for example, A
The l composition can be further increased, and a semiconductor laser having a real refractive index structure excellent in the effect of confining light in the waveguide can be realized.

For example, when the current blocking layer has a superlattice structure in which first layers made of GaN and second layers made of AlGaN are alternately and repeatedly laminated, the second layers containing Al are individually formed. Since the layer thickness may be small, the strain due to the difference in thermal expansion coefficient between the current blocking layer and the underlying layer such as the cladding layer is relaxed.

In this case, when the Al composition ratio is 0.5 or less, the second layer needs to have a layer thickness of about 200 to 500 Å, and when the Al composition ratio is 0.75 or less, The thickness needs to be about 100 to 200Å, and when the Al composition ratio is 1 or less, the layer thickness needs to be about 10 to 100Å. The first layer can have a thickness of about 10 to 1000 Å regardless of the thickness of the second layer and the Al composition ratio, but the thickness is preferably the same as that of the second layer.

Further, the current blocking layer is a first layer made of AlGaN, and Al having a larger Al composition than the first layer.
In the case of a superlattice structure in which the second layer made of GaN is alternately and repeatedly laminated, the second layer having a large Al composition may have a small layer thickness of each layer, and thus the current blocking layer and the clad layer, etc. The strain due to the difference in the coefficient of thermal expansion with the underlying layer is relaxed.

Further, the present invention is a semiconductor laser in which the current blocking layer is made of Al _X Ga _{1 -X} N, and in the layer constituting the superlattice structure of the current blocking layer, A
A layer having a large l composition has a smaller carrier concentration than a layer having a small Al composition or a layer not containing Al.

In this case, the band barrier in the current blocking layer becomes high, and the current blocking action in the current blocking layer is improved.

In the semiconductor laser of the present invention, the current blocking layer is made of In _Y Ga _{1 -Y} N (where 0 ≦ Y ≦ 1), and the superlattice structure is made up of a plurality of layers having different Y values. Is characterized in that.

In this case, even if the average In composition in the entire current block layer is increased or the layer thickness of the current block layer is increased, the decrease in crystallinity of the current block layer can be suppressed. Therefore, for example, I
The n composition can be further increased, and a semiconductor laser having a loss guide structure excellent in light absorption in the current blocking layer can be realized.

For example, in the case where the current blocking layer has a superlattice structure in which first layers made of GaN and second layers made of InGaN are alternately and repeatedly laminated, each of the second layers containing In is Since the layer thickness may be small, the strain due to the difference in lattice constant between the current blocking layer and the underlying layer such as the cladding layer is relaxed.

In this case, when the In composition ratio is 0.4 or less, the second layer needs to have a layer thickness of about 100 to 300 Å. When the In composition ratio is 0.6 or less, the second layer is a layer. Thickness is 1
It is necessary to set it to 0-100Å. Also, the first layer is
10 to 1000 regardless of the thickness of the second layer and the In composition ratio
It can be about Å, but is preferably about the same as the thickness of the second layer.

Further, the current blocking layer is a first layer made of InGaN and In having a larger In composition than the first layer.
In the case of a superlattice structure in which the second layers made of GaN are alternately and repeatedly laminated, the layer thickness of each of the second layers having a large In composition may be small, so that the current blocking layer and the cladding layer, etc. The strain due to the difference in the lattice constant with the underlying layer is relaxed.

In the present invention, the current blocking layer is In
_{In the} semiconductor laser made of _Y Ga _{1 -Y} N, among the layers forming the superlattice structure of the current blocking layer, the layer having a larger In composition is more carrier than the layer having a smaller In composition or a layer not containing In. It is characterized by high concentration.

In this case, the band barrier in the current blocking layer becomes high, and the current constriction action in the current blocking layer is improved.

Further, in the semiconductor laser of the present invention, a first clad layer, an active layer and a second clad layer made of a nitride semiconductor material are sequentially formed, and the second clad layer is formed on the active layer.
In a semiconductor laser in which a current block layer for confining a current flowing through the active layer is formed on the clad layer side, the current block layer is a layer in which a first current block layer and a second current block layer are sequentially formed, The first current blocking layer has a superlattice structure including an i-type semiconductor layer.

In the semiconductor laser having such a structure, the first
Since the layer thickness of each layer of the superlattice structure forming the current blocking layer is small, the strain between the second cladding layer and the current blocking layer is relaxed. Further, since the high-resistance first current blocking layer exists between the second current blocking layer and the second cladding layer, when a forward voltage is applied, the first current blocking layer and the second cladding layer are separated from each other. The space is depleted, the device capacitance is reduced, and as a result, the light output rises and falls quickly.

Further, the semiconductor laser of the present invention comprises the second
The current blocking layer is a layer having a semiconductor layer of a conductivity type different from that of the second cladding layer.

In this case, the function of blocking the current in the current blocking layer is enhanced in the semiconductor laser whose light output rises and falls quickly.

Further, the second current blocking layer has a superlattice structure composed of a plurality of layers.

In this case, even if the average Al composition or In composition in the entire second current block layer is increased or the layer thickness of the current block layer is increased, the crystallinity of the second current block layer is not deteriorated. It can be suppressed. So, for example,
By increasing the Al composition further than that of the second clad layer, the semiconductor laser having a real refractive index structure excellent in the effect of confining light in the waveguide, or by increasing the In composition further than that of the second clad layer, It is possible to realize a semiconductor laser with a loss guide structure that is excellent in light absorption in the current blocking layer.

The semiconductor laser of the present invention is characterized in that the first current blocking layer is doped with at least one of Zn, Be, Ca and C.

In this case, the first current blocking layer is 1.5
The layer has a sufficiently high resistance of Ω · cm or more.

In the semiconductor laser of the present invention, the first current blocking layer is i-type GaN or i-type In.
The superlattice structure is characterized in that a first layer made of GaN and a second layer made of i-type InGaN having a larger In composition than the first layer are alternately and repeatedly laminated.

In this case, the device capacitance can be sufficiently reduced even in the semiconductor laser having a current block layer containing In and having a small band gap, and as a result,
The current blocking effect can be enhanced and the rise and fall of the optical output can be accelerated.

Further, the semiconductor laser of the present invention is characterized in that the first layer is in contact with the second cladding layer.

As a result, the first band gap has a large value.
Since the layer is in contact with the second cladding layer, the band gap can be gradually reduced from the second cladding layer toward the current blocking layer. As a result, the rise and fall of the light output becomes even faster.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a semiconductor laser according to the first embodiment, which is an embodiment of the present invention.

The semiconductor laser of the first embodiment is a ridge waveguide type semiconductor laser, and is undoped i-Al _0.5 on the c-plane of the sapphire substrate 1 by MOCVD.
Ga _{0 .5} thickness 300Å consisting of N buffer layer 2, a thickness of 3μm consisting n-GaN of the i-GaN layer 3, Si-doped thick 2μm of undoped i-GaN n-
GaN layer 4, Si-doped n-In _0.1 Ga _0.9 N with a thickness of 0.1 μm n-crack preventive layer 5, Si-doped n-Al _0.10 Ga _0.90 N with a thickness of 0.7 μm
-Cladding layer 6, active layer 7 having a multiple quantum well structure made of Si-doped n-InGaN, Mg-doped p-Al
0.7 μm thick p-cladding layer 8 made of _0.10 Ga _0.90 N, 0.2 μm thick made of Mg-doped p-GaN
The p-cap layer 9 is formed of a semiconductor wafer in which the p-cap layer 9 is sequentially stacked.

The active layer 7 is made of GaN and has a thickness of 0.
In _0.03 Ga _0.97 N between a pair of 1 μm light guide layers
This is a multiple quantum well structure in which a 60 Å thick barrier layer made of In and a 30 Å well layer made of In _0.13 Ga _0.87 N are alternately formed.

On the semiconductor wafer, a striped ridge portion 10 is formed by removing the p-cladding layer 8 to a predetermined depth by reactive ion etching or reactive ion beam etching, and n- is formed by the same etching.
The GaN layer 4 is removed to a predetermined depth and the electrode forming surface 11
Are formed. The ridge portion 1 of the p-clad layer 8
Since the thickness of the flat portion other than 0 is used for the transverse mode control,
It is preferably 0.05 to 0.4 μm.

Further, a current blocking layer 12 having a superlattice structure and having a thickness of 0.5 μm, which will be described later, is formed in the etching-removed portion on the p-clad layer 8, and is formed on the p-cap layer 9 and the current blocking layer. On top of 12, is Mg-doped p-Ga.
A p-contact layer 13 made of N and having a thickness of 0.2 μm is formed. A p-electrode 14 is formed on the upper surface of the p-contact layer 13, and an n-electrode 15 is formed on the electrode formation surface 11 of the n-clad layer 4.

As shown in FIG. 2, the current blocking layer 12 is composed of a first layer 12a of Si-doped n-GaN having a thickness of 250 Å and a small amount of undoped i-Al _0.30 Ga _0.70 N or Si. This is a superlattice structure in which ten layers each of which is made of n-Al _0.30 Ga _0.70 N and the second layer 12 b having a thickness of 250 Å are formed alternately.

The Si-doped carrier concentration of the first layer 12a is 3 × 10 ¹⁸ cm ^-3 . When the second layer 12b is a Si-doped layer, the Si-doped carrier concentration is 1 × 10 ¹⁷ cm ^{−3, which} is lower than that of the first layer 12a.
is there.

In the semiconductor laser of the first embodiment as described above, the current blocking layer 12 does not contain Al.
It has a superlattice structure in which a and a second layer 12b containing Al are alternately and repeatedly laminated. Since the second layer 12b containing Al composition has a small individual layer thickness, the second layer 12b containing a The strain due to the difference in expansion coefficient is relaxed. Therefore, as compared with the case where the current blocking layer 12 is formed of a single layer, the Al composition and the thickness can be increased without lowering the crystallinity.

In the current blocking layer 12, the first layer 12a containing no Al has a high carrier concentration, and the second layer 12b containing Al has a low carrier concentration. As shown in 3, the current blocking effect is improved and the current blocking effect is improved.

As another example of the first embodiment, the current blocking layer 12 is made of Si-doped n-Al _0.05 Ga _0.95 N.
The first layer 12a having a thickness of 250 Å and the second layer 12b having a thickness of 250 Å made of undoped i-Al _0.25 Ga _0.75 N or n-Al _0.25 Ga _0.75 N lightly doped with Si are alternately formed. A superlattice structure in which layers are formed may be used.

This is an example in which the current blocking layer 12 is formed by the superlattice structure of the first layer 12a having a small Al composition and the second layer 12b having a large Al composition. Since the individual thicknesses of the two layers 12b are small, the strain due to the difference in thermal expansion coefficient from the p-cladding layer 8 is relaxed. Therefore, the current blocking layer 12
Can increase the Al composition and the thickness without lowering the crystallinity as compared with the case of forming a single layer.

In the current blocking layer 12, the first layer 12a having a small Al composition has a large carrier concentration, and the second layer 12b having a large Al composition has a small carrier concentration. As shown in 3, the current blocking effect is improved and the current blocking effect is improved.

As described above, in the semiconductor laser of the first embodiment, the Al composition and the thickness of the current block layer 12 can be increased and the thickness can be increased without deteriorating the crystallinity. Since a sufficient amount of light is confined therein and the current blocking effect is improved, a semiconductor laser having a real refractive index guide structure with good emission efficiency is obtained.

Further, as the semiconductor laser of the second embodiment of the present invention, instead of the current blocking layer 12 of the first embodiment, the current blocking layer 12 is an undoped i-GaN or, as shown in FIG. N-G lightly doped with Si
A first layer 12c made of aN and having a thickness of 250 Å and a second layer 12c having a thickness of 250 Å and made of Si-doped n-In _0.3 Ga _0.7 N.
It may be a superlattice structure in which 10 layers are alternately formed with 12 layers.

The Si-doped carrier concentration of the second layer 12d is 3 × 10 ¹⁸ cm ^-3 . When the first layer 12c is a Si-doped layer, the Si-doped carrier concentration is 1 × 10 ¹⁷ cm ^−3, which is lower than that of the second layer 12d.

In the semiconductor laser of the second embodiment as described above, the current blocking layer 12 is the first layer 12 containing no In.
The second layer 12 containing In has a superlattice structure in which c and a second layer 12d containing In are alternately and repeatedly stacked.
Since the individual layer thickness of d is small, the strain due to the difference in lattice constant from the p-cladding layer 8 is relaxed. Therefore, the current blocking layer 12 can have a larger In composition and a larger thickness without lowering the crystallinity, as compared with the case where it is formed as a single layer.

In the current blocking layer 12, the first layer 12c containing no In has a small carrier concentration, and the second layer 12d containing In has a large carrier concentration. As shown in FIG. 5, it becomes higher and the current blocking effect is improved.

As another example of the second embodiment, the current blocking layer 12 is made of undoped i-In _0.05 Ga _0.95 N.
Alternatively, n-In _0.05 Ga _0.95 N lightly doped with Si
The superlattice structure may be formed by alternately forming 10 layers of the first layer 12c having a thickness of 250Å and the second layer 12d having a thickness of 250Å made of Si-doped n-In _0.25 Ga _0.75 N.

This is an example in which the current blocking layer 12 is constituted by the superlattice structure of the first layer 12c having a small In composition and the second layer 12d having a large In composition. Since the individual thicknesses of the two layers 12d are small, the strain due to the difference in lattice constant from the p-cladding layer 8 is relaxed. Therefore, the current blocking layer 12 is
Compared with the case of forming a single layer, the In composition and the thickness can be increased without lowering the crystallinity.

In the current blocking layer 12, the first layer 12c having a small In composition has a small carrier concentration, and the second layer 12d having a large In composition has a large carrier concentration. Therefore, the band barrier in the current blocking layer 12 is As shown in FIG. 5, it becomes higher and the current blocking effect is improved.

As described above, in the semiconductor laser of the second embodiment, the current composition of the current blocking layer 12 can be increased and the thickness thereof can be increased without deteriorating the crystallinity. At 12 the light is fully attenuated,
Moreover, since the current blocking effect is improved, the semiconductor laser has a loss guide structure with good light emission efficiency.

Further, in the above-mentioned first and second embodiments, the case where the present invention is applied to the ridge waveguide type semiconductor laser has been described, but the present invention is not limited thereto, for example, as shown in FIG. In the self-aligned structure semiconductor laser, the current blocking layer may be configured in the same manner as in the above-described embodiments.

In FIG. 6, reference numeral 21 is a sapphire substrate. On the c-plane of the sapphire substrate 21, a buffer layer 22 made of undoped i-Al _0.5 Ga _0.5 N and having a thickness of 300 Å and having a thickness of 2 μm is formed by MOCVD. Undoped i-GaN layer 23, 3 μm thick Si-doped n-Ga
N layer 24, Si-doped n-In _0.1 Ga _0.9 N crack preventing layer 25 with a thickness of 0.1 μm, Si-doped n
-Al _0.1 Ga _0.9 N 0.7 μm thick n-clad layer 26, Si-doped n-InGaN multiple quantum well structure active layer 27, Mg-doped p-Al _0.1
The first p-clad layer 28 having a thickness of 0.2 μm made of Ga _0.9 N, the current blocking layer 29 having a thickness of 0.5 μm having a superlattice structure, and the thickness of 0.5 μm made of p-Al _0.1 Ga _0.9 N doped with Mg. Second p-cladding layer 30, Mg-doped p
-0.2 μm thick p-contact layer 3 made of GaN
A semiconductor wafer is formed by laminating 1 in order.
Incidentally, the current blocking layer 29 has a window portion 35 serving as a current passage removed by etching. Further, on this semiconductor wafer, the electrode formation surface 32 is formed by removing the n-GaN layer 24 to a predetermined depth by reactive ion etching or reactive ion beam etching. A p-electrode 33 is formed on the upper surface of the p-contact layer 31, and n-
An n-electrode 34 is formed on the electrode forming surface 32 of the clad layer 24.

The current block layer 29 is formed of a superlattice structure having the same structure as that of the ridge waveguide type current block layer 12 described above, and has a real refractive index guide structure of a semiconductor laser or a loss guide structure of good luminous efficiency. It becomes the semiconductor laser of.

Although the sapphire substrate is used as the substrate in the above-mentioned embodiments, it may be made of other materials such as SiC, spinel, and GaN.

Further, the semiconductor material of the current blocking layer may be one having P or As as a V group element.

Further, as a doping material for the layer forming the superlattice structure of the current blocking layer, Ge is used instead of Si.
Other elements such as Alternatively, Zn or the like may be doped to form a high resistance current blocking layer.

Next, a semiconductor laser according to the third embodiment, which is an embodiment of the present invention, will be described.

FIG. 7 is a sectional view showing the structure of the semiconductor laser of the third embodiment. The same parts as those in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted.

In the semiconductor laser of the third embodiment, the current blocking layer 12 includes the i-type first current blocking layer 121 formed from both side surfaces of the ridge portion 10 to the upper surface of the p-cladding layer 8. It is composed of an n-type second current block layer 122 formed on the first current block layer 121.

As shown in FIG. 8, the first current blocking layer 121 includes a first layer 121a made of i-GaN doped with impurities and having a thickness of 250 Å and an i-doped layer doped with impurities.
It is a high-resistance superlattice structure in which 10 layers of the second layers 121 b of InGaN having a thickness of 250 Å are alternately formed. The impurities doped into the first layer 121a and the second layer 121b include Zn (zinc), Be (beryllium),
At least one of Ca (calcium) and C (carbon) is used, and by doping this impurity, the first layer 121a and the second layer 121b become i-type semiconductor layers,
It becomes a high resistance layer. The first layer 121a is in contact with the p-clad layer 8.

The second current blocking layer 122 has a structure as shown in FIG.
As shown in FIG. 1, the first 250-Å-thick first layer composed of undoped i-GaN or n-GaN lightly doped with Si.
This is a superlattice structure in which five layers 122 a and second layers 122 b made of Si-doped n-In _0.3 Ga _0.7 N and having a thickness of 250 Å are alternately formed. The p-contact layer 13 is formed on the second current block layer 122.

In the semiconductor laser of the third embodiment, since the first current blocking layer 121 and the second current blocking layer 122 constituting the current blocking layer 12 each have a superlattice structure composed of thin layers. , Current blocking layer 1
The strain generated due to the difference in lattice constant between 2 and the p-cladding layer 8 is relaxed. Therefore, the composition ratio of In can be increased in the first current blocking layer 121 and the second current blocking layer 122, and the total film thickness can be increased.

Further, since the high-resistance first current blocking layer 121 is formed between the p-type p-cladding layer 8 and the n-type second current blocking layer 122, the p-electrode 14 and the n-type current blocking layer 121 are formed.
-When a voltage is applied in the forward direction to the -electrode 15, the space between the second current block layer 122 and the p-clad layer 8 is sufficiently depleted, and the device capacitance is sufficiently reduced. For this reason,
The function of blocking the current in the current blocking layer 12 is enhanced, and the rise and fall of the light output when the element is pulse-driven becomes faster. Particularly, in the third embodiment, the first layer 121 of the first current blocking layer 121 in contact with the p-clad layer 8 is formed.
Since a is a layer that does not contain In and has a bandgap larger than that of the other second layer 121b, the rise and fall of the light output becomes faster.

In the third embodiment described above, the first layer 121a of the first current blocking layer 121 and the first layer 122a of the second current blocking layer 122 are made of GaN, but the first layer 121a, At least one layer of 122a may be formed of a layer containing In, for example, In _0.05 Ga _0.95 N.

Also in such a structure, similarly to the third embodiment described above, the function of blocking the current by the current blocking layer 12 is enhanced, and the rise and fall of the light output when the element is pulse-driven is fast. Become. In particular, the first layer 121a of the first current blocking layer 121 that is in contact with the p-clad layer 8
However, the composition ratio of In is smaller than that of the other second layer 121b,
In the case of a layer having a large band gap, the rise and fall of the optical output will be faster.

As described above, in the semiconductor laser of the third embodiment, the current composition of the current block layer 12 can be increased and the thickness thereof can be increased without deteriorating the crystallinity. At 12 the light is fully attenuated,
In addition, the current blocking effect is improved, and in addition, the device capacitance is reduced, so that the semiconductor laser has a loss guide structure with good light emission efficiency and high-speed operation.

Further, in the above-mentioned third embodiment, the case where the present invention is applied to the ridge waveguide type semiconductor laser has been described, but the present invention has another structure, for example, the self-alignment as shown in FIG. Even in the structure of semiconductor laser,
The current blocking layer may be constructed in the same manner as in the above embodiment.

Although the sapphire substrate is used as the substrate in the above-mentioned third embodiment, it may be made of another material such as SiC, spinel or GaN.

The semiconductor material of the current blocking layer may be one having P or As as a V group element.

Further, as the doping material for the layer forming the superlattice structure of the second current blocking layer, another element such as Ge may be used instead of Si. Alternatively, Zn or the like may be doped to form a high resistance current blocking layer.

In the embodiment of the present invention, n-type, p-type
The type and the i type are abbreviated as n-, p-, and i-, respectively.

[0079]

According to the present invention, the current blocking layer can be formed to a sufficient thickness while suppressing the deterioration of crystallinity such as cracks, and the Al composition, the In composition, etc. can be increased. It is possible to provide a semiconductor laser having an excellent light confinement effect or light absorption effect in the current blocking layer.

Further, according to the present invention, in addition to the above-mentioned effects, the device capacitance is reduced, so that the semiconductor laser which can improve the luminous efficiency and can operate at high speed can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall structure of a ridge waveguide type semiconductor laser according to first and second embodiments of the present invention.

FIG. 2 is a sectional view showing a configuration of a current blocking layer in the semiconductor laser of the first embodiment of the present invention.

FIG. 3 is a diagram showing an energy band of a current blocking layer in the semiconductor laser of the first embodiment of the present invention.

FIG. 4 is a sectional view showing a structure of a current blocking layer in a semiconductor laser according to a second embodiment of the present invention.

FIG. 5 is a diagram showing an energy band of a current blocking layer in a semiconductor laser according to a second embodiment of the present invention.

FIG. 6 is a sectional view showing an overall configuration of a semiconductor laser having a self-aligned structure corresponding to the first and second embodiments.

FIG. 7 is a sectional view showing the overall structure of a ridge waveguide type semiconductor laser according to a third embodiment of the present invention.

FIG. 8 is a sectional view showing a structure of a current block layer in a semiconductor laser according to a third embodiment of the present invention.

FIG. 9 is a sectional view showing a structure of a current blocking layer in a semiconductor laser according to a third embodiment of the present invention.

FIG. 10 is a sectional view showing an overall configuration of a semiconductor laser having a self-aligned structure corresponding to a third embodiment.

[Explanation of symbols]

7 Active layer 12 Current blocking layer 12a first layer 12b second layer 12c first layer 12d second layer 27 Active layer 29 Current blocking layer 121 First Current Blocking Layer 121a First layer 121b Second layer 122 Second Current Blocking Layer 122a First layer 122b second layer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiko Nomura 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-10-126010 (JP, A) Flat 6-61588 (JP, A) JP-A-11-251685 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (10)

(57) [Claims] 1. An n-type crystal made of a nitride semiconductor material.
And a p-type clad layer are sequentially formed,
Flow to the active layer on the side of the p-type cladding layer with respect to the active layer.
With a current blocking layer to confine the current flow
In the semiconductor laser of the system, the current blocking layer is Al
_X Ga _1-X N (where 0 ≦ X ≦ 1) and the value of X above
Is a superlattice structure composed of a plurality of different layers,
Al composition of the layers constituting the superlattice structure of the block layer
The first layer with a small or no Al content is doped
Second layer which is a layer doped with a material and has a large Al composition
Is undoped or a doping material more than the first layer
It is a layer with a low carrier concentration due to the doping of
Semiconductor lasers to collect. 2. The first layer is made of GaN, and the second layer is made of GaN.
The layer is made of AlGaN.
Semiconductor lasers. 3. The first layer is made of AlGaN, and
AlGaN whose second layer has a higher Al composition than said first layer
The semiconductor laser according to claim 1, wherein the semiconductor laser comprises: 4. An n-type cladding made of a nitride-based semiconductor material.
And a p-type clad layer are sequentially formed,
Flow to the active layer on the side of the p-type cladding layer with respect to the active layer.
With a current blocking layer to confine the current flow
In a semiconductor laser of the system, the current flowing in the active layer is
The constricted current block layer is In _Y Ga _1-Y N (where 0 ≦
Y ≦ 1), and is composed of a plurality of layers having different Y values.
And a superlattice structure of the current blocking layer
Of the layers forming
The first layer not containing is undoped or a doping material
Is a doped layer, and the second layer with a large In composition is
Carriers by doping with a doping material rather than the first layer
A semiconductor laser having a high-concentration layer . 5. The first layer is made of GaN, and the second layer is made of GaN.
5. The layer of InGaN as claimed in claim 4, characterized in that
Semiconductor lasers. 6. The first layer is made of InGaN, and
InGaN in which the second layer has a larger In composition than the first layer
5. The semiconductor laser according to claim 4, comprising: 7. A first class composed of a nitride-based semiconductor material.
A pad layer, an active layer, and a second cladding layer are sequentially formed, and
Flow to the active layer on the side of the second cladding layer with respect to the active layer
Semiconductor layer on which a current blocking layer that narrows the current
The current block layer is a first current block
A layer and a second current blocking layer formed in order,
The first current blocking layer is i-type GaN or i-type
First layer of InGaN, and In group more than the first layer
Alternating with the second layer of i-type InGaN
The superlattice structure is repeatedly laminated, and
The flow blocking layer has a conductivity type different from that of the second cladding layer.
A semiconductor laser comprising a layer having a semiconductor layer . 8. The second current blocking layer comprises a plurality of layers.
The semiconductor laser according to claim 7, wherein the semiconductor laser has the following superlattice structure . 9. The first current blocking layer comprises Zn, B
at least one of e, Ca and C is doped
9. The semiconductor laser according to claim 7, which further comprises: 10. The first layer is in contact with the second cladding layer.
The semiconductor laser according to claim 7, 8 or 9, wherein