JPH08111566A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To realize a semiconductor light emitting element of low threshold current density and long service life whose clad layer is formed of ZnMgSSe compound semiconductor. CONSTITUTION: An N-type Zn1-p Mgp Sq Se1-q clad layer 3, an N-type ZnSu Se1-u optical waveguide layer 4, an active layer 5, a P-type ZnSu Se1-u optical guide layer 6, and a P-type Zn1-p Mgp Sq Se1-q clad layer 7 are laminated on an N-type GaAs substrate 1 for the formation of a semiconductor laser, wherein the composition ratio p of Mg in the N-type Zn1-p Mgp Sq Se1-q clad layer 3 is so set as to satisfy a formula, 0.10<p<=0.20.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor light emitting device, and more particularly to a semiconductor light emitting device capable of emitting blue or green light, such as a semiconductor laser or a light emitting diode.

[0002]

2. Description of the Related Art In recent years, semiconductor light emitting devices capable of emitting blue or green light have been actively researched for the purpose of high density optical recording and application to light sources for displays.

As a material used for manufacturing such a semiconductor light emitting device capable of emitting blue or green light, II-VI is used.
Group compound semiconductors are promising. In particular, quaternary II-V
It is known that a ZnMgSSe-based compound semiconductor, which is a group I compound semiconductor, is suitable as a material for a clad layer or an optical waveguide layer when a blue or green light emitting semiconductor laser having a wavelength of 400 to 550 nm is formed on a GaAs substrate. (Eg, Electron. Lett. 28 (1992) 1798).

As a semiconductor laser for emitting blue to green light using the II-VI group compound semiconductor, GaAs is used.
A semiconductor laser having a substrate, a cladding layer made of ZnMgSSe-based compound semiconductor, an optical waveguide layer made of ZnSSe-based compound semiconductor, and an active layer made of ZnCdSe-based compound semiconductor has been previously proposed by the applicant, and at room temperature. Successful pulse oscillation at a wavelength of 480.5 nm (Electron. Lett. 30 (1994) 415). Here, the Mg composition ratio of the ZnMgSSe-based compound semiconductor forming the cladding layer is 0.10, and the S composition ratio is 0.18.
And the Cd composition ratio of the ZnCdSe-based compound semiconductor forming the active layer is 0.08. At this time, the band gap E _g of the clad layer at the liquid nitrogen temperature (77 K)
Is 2.98 eV, and the band gap difference ΔE _g between the active layer and the cladding layer is 0.26 eV.

Further, thereafter, using a GaAs substrate, the cladding layer is made of ZnMgSSe compound semiconductor, the optical waveguide layer is made of ZnSe compound semiconductor, and the active layer is made of ZnC.
A semiconductor laser composed of a dSe-based compound semiconductor has been proposed by the present applicant, and has a wavelength of 5 at room temperature.
Successful continuous oscillation at 23.5 nm (Japanese Patent Application No. 5-1
84436). Here, ZnM forming the clad layer
The Mg composition ratio of the gSSe-based compound semiconductor is 0.09, and the S composition ratio is 0.18.
The Cd composition ratio of the Se-based compound semiconductor is 0.19.

[0006]

However, the above-mentioned conventional semiconductor laser having the cladding layer made of ZnMgSSe type compound semiconductor still has problems in reduction of threshold current density and prolongation of life. The solution was desired.

Therefore, an object of the present invention is to provide a semiconductor light emitting device having a low threshold current density, which uses a ZnMgSSe compound semiconductor as a material for the cladding layer.

Another object of the present invention is to provide a long-life semiconductor light emitting device using a ZnMgSSe compound semiconductor as a material for the cladding layer.

[0009]

As a result of intensive studies to solve the above problems, the present inventor has found that one of the reasons why the conventional semiconductor lasers described above have a low threshold current density and an insufficient lifetime. First, ZnMgSSe forming the clad layer
It has been found that the optimization of the composition of the system compound semiconductor may be insufficient. This is due to insufficient knowledge of the physical properties of ZnMgSSe-based compound semiconductors. In particular, regarding Cl-doped n-type ZnMgSSe used as the material for the n-type cladding layer, ZnM
effective donor concentration as the band gap E _g of gSSe increases N _D -N _A (N _D: donor concentration, N _A: acceptor concentration) and regions is saturated, a donor impurity, i.e. such ionization energy of Cl Ever Not examined in detail. Cl constituting the n-type cladding layer
It is important to know the electrical and optical characteristics of the doped n-type ZnMgSSe, since they have a great influence on various characteristics of the semiconductor laser.

Therefore, the present inventor has found that Cl-doped n-type Zn
Various experiments were conducted to obtain more detailed knowledge about the electrical characteristics and optical characteristics of MgSSe, and the following results were obtained.

FIG. 1 shows the relationship between the band gap E _g of Cl-doped n-type ZnMgSSe at 77 K and the ionization energy E _d of Cl used as a donor impurity. Here, E _d was obtained by Hall measurement at room temperature (the same applies hereinafter). As can be seen from FIG.
_g E _d is going to become gradually increases as increases, it is rapidly increasing in the border in the vicinity of E _g = 3.10eV. Further, FIG. 2 shows the relationship between the Mg composition of Cl-doped n-type ZnMgSSe and E _d . It can be seen from FIG. 2 that E _d gradually increases as the Mg composition increases, and increases sharply at the boundary of the Mg composition = 20%.

Here, when E _d becomes large, the trapping of carriers (electrons) occurs along with lattice relaxation and becomes a non-emission center, so that the light emission efficiency of the semiconductor light emitting device is reduced, leading to deterioration in characteristics.

[0013] Figure 3 shows the relationship between the Cl-doped E _g of the n-type ZnMgSSe of 77K and N _D -N _A and the carrier concentration (electron concentration). Figure 4 shows the relationship between the Mg composition and N _D -N _A and carrier concentration of the Cl-doped n type ZnMgSSe. Here, N _D -N _A capacity at room temperature - was determined by the voltage (C-V) measurements, and so forth. The sample used for these measurements had a Cl doping amount of 3 × 1.
It is 0 ¹⁷ cm ^-3 . As can be seen from FIGS. 3 and 4,
E _g is more than 3.10 eV, the Mg composition becomes 20% or more with N _D -N _A and the carrier concentration begins to decrease rapidly.

Even when the band gap E _g of Cl-doped n-type ZnMgSSe exceeds 3.10 eV, in other words, even when the Mg composition exceeds 20%, Cl
By sufficiently increasing the doping amount of, the carrier concentration can be sufficiently increased.

FIG. 5 shows the activation rates N _D -N _A / [C of Cl-doped n-type ZnMgSSe at 77 K in E _g and Cl.
l] (where [Cl] is Cl in n-type ZnMgSSe
The doping concentration of the above). In addition, FIG. 6 shows C
showing the relationship between l activation rate of doped n-type ZnMgSSe the Mg composition and _{Cl N D -N A / [Cl} ]. From FIG. 5 and FIG. 6, it can be seen that the activation rate of Cl is greatly reduced when the E _g is 3.10 eV or more and the Mg composition is 20% or more as described above. This is because some of the Cl atoms taken into the growth layer enter the interstitial position or the reverse position without being activated, and these become defects such as non-radiative centers.

Defects such as these non-radiative centers existing in the vicinity of the active layer have a serious influence on the life of the semiconductor light emitting device, and it is impossible to remove these defects and improve the crystallinity of the growth layer. , Is important for extending the life of the semiconductor light emitting device.

The present invention was devised on the basis of the above findings obtained by the present inventor. That is, in order to achieve the above object, a semiconductor light emitting device according to the present invention uses a compound semiconductor substrate, and has an n-type cladding layer and a p-type clad layer made of a ZnMgSSe-based compound semiconductor on both sides of an active layer made of a II-VI group compound semiconductor. In a semiconductor light emitting device having a structure sandwiched by a clad layer, M of ZnMgSSe-based compound semiconductor constituting an n-type clad layer is formed.
The g composition ratio is greater than 0.10 and 0.20 or less.

In the present invention, from the viewpoint of improving the characteristics of the n-type cladding layer, the Mg composition ratio of the ZnMgSSe-based compound semiconductor forming the n-type cladding layer is preferably larger than 0.10. It is set to 0.18 or less.

In the present invention, since the MgMg composition ratio of the ZnMgSSe type compound semiconductor forming the n-type clad layer is larger than 0.10 and 0.20 or less, the compound semiconductor substrate and the n-type clad layer are formed. Make up Z
0.25% lattice mismatch with nMgSSe compound semiconductor
It can be within.

In the present invention, from the viewpoint of improving the characteristics of the n-type cladding layer, typically, the band gap of the ZnMgSSe-based compound semiconductor forming the n-type cladding layer is 3.10 eV or less at the liquid nitrogen temperature. Is set.

In the present invention, the active layer is, for example, Z
nCdSe-based compound semiconductor, ZnSe-based compound semiconductor,
It is composed of a ZnSSe-based compound semiconductor or a ZnMgSSe-based compound semiconductor.

In the present invention, the band gap difference ΔE _g between the active layer and the cladding layer is at least 0.25 eV in order to obtain good carrier confinement characteristics and optical confinement characteristics as conditions for stable room temperature laser oscillation.
The above is set. Therefore, when the upper limit of the band gap of the ZnMgSSe-based compound semiconductor forming the n-type cladding layer at the liquid nitrogen temperature is set to 3.10 eV as described above, the upper limit of the band gap of the active layer is 3.10−.
It becomes 0.25 = 2.85 eV.

Further, the shortest wavelength of 480.5 achieved so far in the above-mentioned conventional semiconductor laser using the cladding layer made of ZnMgSSe type compound semiconductor.
nm (oscillation wavelength in room temperature pulse oscillation), in order to enable oscillation at a shorter wavelength, the bandgap of the active layer is the active layer (Cd composition ratio = 0) of the semiconductor laser in which this shortest wavelength of 480.5 nm is obtained. ZnCdSe of 0.08)
Band gap of 2.98-0.26 = 2.
It should be larger than 72 eV.

The band gap of the active layer has an upper limit (2.
85 eV) and more than 2.72 eV, specific examples of the material include ZnCdSe-based compound semiconductors having a Cd composition ratio of less than 0.08 and ZnSSe-based compound semiconductors having an S composition ratio of 11% or less. , ZnSe-based compound semiconductors, and the like. A ZnMgSSe-based compound semiconductor having an Mg composition ratio of 0.02 and an S composition ratio of 0.08 is an example that meets this condition and lattice-matches with the compound semiconductor substrate.

In an exemplary embodiment of the invention,
The semiconductor light emitting device includes a first optical waveguide layer and a second optical waveguide layer between the active layer and the n-type cladding layer and the p-type cladding layer, respectively.
Optical waveguide layer, and the first optical waveguide layer and the second optical waveguide layer are made of ZnSSe compound semiconductor or ZnSe compound semiconductor.

In the present invention, the compound semiconductor substrate is typically a GaAs substrate, but a GaP substrate or the like may be used.

In the present invention, the semiconductor light emitting device is a semiconductor laser or a light emitting diode.

[0028]

According to the semiconductor light emitting device of the present invention constructed as described above, ZnMg constituting the n-type cladding layer is formed.
Since the Mg composition ratio of the SSe-based compound semiconductor is more than 0.10 and not more than 0.20, the band gap of the n-type cladding layer at the liquid nitrogen temperature is more than 2.98 eV and not more than 3.10 eV. The band gap of the n-type cladding layer in the conventional semiconductor laser described above can be made sufficiently large. Therefore, the band gap difference between the active layer and the n-type clad layer can be made sufficiently larger than 0.25 eV, and the band gap difference between the active layer and the p-type clad layer is also 0.
By setting it to be larger than 25 eV, good carrier confinement characteristics and optical confinement characteristics can be obtained. Further, since the ionization energy of the donor impurity in the n-type clad layer can be suppressed to be small, it is possible to prevent the luminous efficiency from decreasing. As described above, when the semiconductor light emitting element is a semiconductor laser, the threshold current density can be reduced, and when the semiconductor light emitting element is a light emitting diode, the operating current density can be reduced. .

Since the activation rate of the donor impurity in the n-type cladding layer can be increased, the density of defects such as non-radiative centers due to the unactivated donor impurity can be reduced. Further, the Mg composition ratio is 0.1
ZnMgSS greater than 0 and less than or equal to 0.20
Since the e-based compound semiconductor is substantially lattice-matched with the compound semiconductor substrate, particularly the GaAs substrate, the composition of the p-type clad layer is selected so as to be lattice-matched with the compound semiconductor substrate, so that the epitaxial growth of each layer constituting the semiconductor light emitting device is performed. Occasionally, dislocations can be prevented from occurring in these layers. As described above, the life of the semiconductor light emitting device can be extended.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. 7 and 8 show a semiconductor laser according to an embodiment of the present invention. Here, FIG. 7 is a sectional view perpendicular to the cavity length direction of this semiconductor laser, and FIG. 8 is a sectional view parallel to the cavity length direction of this semiconductor laser. This semiconductor laser is a so-called SCH (Separate
Confinement Heterostructure) structure.

As shown in FIGS. 7 and 8, in the semiconductor laser according to this embodiment, n-type Ga having a (100) plane orientation doped with, for example, Si as a donor impurity.
On the As substrate 1, an n-type ZnSe buffer layer 2 doped with Cl as a donor impurity, and an n-type Zn _1-p Mg _p S _q S doped with Cl as a donor impurity, for example.
e _1-q cladding layer 3, n-type ZnS _u Se _1-u optical waveguide layer 4 doped with Cl as a donor impurity, active layer 5, p doped with N as an acceptor impurity, for example.
Type ZnS _u Se _1-u optical waveguide layer 6, p-type Zn _1-p Mg _p S _q Se doped with, for example, N as an acceptor impurity
_1-q cladding layer 7, p-type ZnS _v Se _1-v layer 8 doped with N as an acceptor impurity, p-type ZnSe contact layer 9 doped with N as an acceptor impurity, and barrier layer made of p-type ZnSe And p-type ZnTe
P-type ZnSe /
A ZnTe multiple quantum well (MQW) layer 10 and a p-type ZnTe contact layer 11 doped with N as an acceptor impurity, for example, are sequentially stacked.

The upper layer of the p-type ZnS _v Se _1-v layer 8, the p-type ZnSe contact layer 9, and the p-type ZnSe / ZnTeMQ
The W layer 10 and the p-type ZnTe contact layer 11 are patterned in a stripe shape. The width of this stripe portion is, for example, about 5 μm.

Further, on the p-type ZnS _v Se _1-v layer 8 other than the above-mentioned stripe portion, for example, a thickness of 300 is provided.
An insulating layer 12 made of an alumina (Al ₂ O ₃ ) film having a thickness of 10 nm is formed. And stripe-shaped p-type ZnT
The p-side electrode 13 on the e-contact layer 11 and the insulating layer 12
Are formed. The portion where the p-side electrode 13 is in contact with the p-type ZnTe contact layer 11 serves as a current path when the semiconductor laser is energized. Here, as the p-side electrode 13, for example, a P layer having a thickness of 10 nm is used.
A Pd / Pt / Au electrode having a structure in which a d film, a Pt film having a thickness of 100 nm, and an Au film having a thickness of 300 nm are sequentially stacked is used. On the other hand, an n-side electrode 14 such as an In electrode is formed on the back surface of the n-type GaAs substrate 1.

In this semiconductor laser, so-called end face coating is applied. That is, as shown in FIG. 8, of the pair of resonator end faces perpendicular to the cavity length direction, the front end face from which laser light is extracted is Al.
_A multilayer film composed of the ₂ O ₃ film 15 and the Si film 16 is coated, and of the pair of resonator end faces perpendicular to the cavity length direction, the rear end face from which laser light is not extracted is Al ₂
A multilayer film in which the O ₃ film 15 and the Si film 16 are stacked for two cycles is coated. Here, the Al ₂ O ₃ film 15 and the S
The thickness of the multilayer film including the i film 16 is selected so that the optical distance obtained by multiplying the refractive index of the i film 16 is equal to 1/4 of the oscillation wavelength of the laser light. By applying such end face coating, for example, the reflectance of the front end face can be 70% and the reflectance of the rear end face can be 95%.

The active layer 5 preferably has a thickness of 2 to 20 nm,
For example, it has a single quantum well structure composed of an i-type Zn _1-z Cd _z Se quantum well layer having a thickness of 6 nm. In this case, the n-type ZnS _u Se _1-u optical waveguide layer 4 and the p-type ZnS _u Se
_{The 1-u} optical waveguide layer 6 constitutes a barrier layer.

The Mg composition ratio p of the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 3 is a value satisfying 0.10 <p ≦ 0.20, for example 0.15, and the S composition ratio q is, for example. 0.22, and the band gap E _{g at} that time is about 3.0 at 77K.
It is 2 eV. M that satisfies this 0.10 <p ≦ 0.20
g composition ratio p (eg, 0.15) and S composition ratio q =
The lattice mismatch between the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 3 having 0.22 and GaAs is within 0.25%, and therefore, the n-type Zn _1-p Mg _p S _q Se _{The 1-q} clad layer 3 is substantially lattice-matched with GaAs. p-type Zn _1-p M
The Mg composition ratio p of the g _p S _q Se _1-q cladding layer 7 is, for example, 0.09, and the S composition ratio q is, for example, 0.18, and the band gap E _{g at} that time is about 2.94 eV at 77K.
Is. This Mg composition ratio p = 0.09 and S composition ratio q
The p-type Zn _1-p Mg _{p Sq} Se _1-q clad layer 7 having = 0.18 is lattice-matched with GaAs. Cd composition ratio z of the i-type Zn _1-z Cd _z Se quantum well layer forming the active layer 5
Is, for example, 0.08, and the band gap E at that time is
_{The g} is about 2.72 eV at 77K. In this case, the Cd composition ratio of the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 3 and the active layer 5 having the Mg composition ratio p = 0.15 = 0.08.
Of the i-type Zn _1-z Cd _z Se quantum well layer has a band gap E _g difference ΔE _g of 0.30 eV, and the Mg composition ratio p = 0.09 is p-type Zn _1-p Mg _p S The difference ΔE _g of the band gap E _g between the _q Se _{1 -q} clad layer 7 and the i-type Zn _1-z Cd _z Se quantum well layer of the Cd composition ratio = 0.08 constituting the active layer 5 is 0. It is 40 eV. The value of the band gap E _g at room temperature can be obtained by subtracting 0.1 eV from the value of the band gap E _g at 77K. The S composition ratio u of the n-type ZnS _u Se _1-u optical waveguide layer 4 and the p-type ZnS _u Se _1-u optical waveguide layer 6 is, for example, 0.06, and the p-type ZnS _v Se _1-v layer 8 is formed. The S composition ratio v of is, for example, 0.06. These S composition ratio u =
The n-type ZnS _u Se _1-u optical waveguide layer 4 and the p-type ZnS _u Se _1-u optical waveguide layer 6 having 0.06 and the S composition ratio v = 0.
P-type ZnS _v Se _1-v layer 8 having a 06 n-type Zn _1-p
Mg _p S _q Se _1-q cladding layer 3 and p-type Zn _1-p M
It is substantially lattice-matched with the g _p S _q Se _1-q cladding layer 7.

I-type Zn _1-z Cd _z S constituting the active layer 5
When the Cd composition ratio z of the e quantum well layer is 0.08 as described above, the oscillation wavelength of this semiconductor laser is about 480 n.
m.

In this example, n-type Zn _1-p Mg _p
The thickness of the S _q Se _1-q clad layer 3 is, for example, 1.2 μm,
N _D -N _A is for example, ^{(2~5) × 10 17 cm -3} .
The thickness of the n-type ZnS _u Se _1-u optical waveguide layer 4 is, for example, 70 n.
m, N _D -N _A is for example, ^{(2~5) × 10 17 cm -3} . The thickness of the p-type ZnS _u Se _1-u optical waveguide layer 6 is, for example 70 nm, is effective acceptor concentration N _A -N _D, for example ^{(2~5) × 10 17 cm -3} . p-type Zn _1-p Mg _p
The thickness of the S _q Se _1-q clad layer 7 is 0.75 μm, for example.
m and N _A -N _D are, for example, 1 × 10 ¹⁷ cm ⁻³ . The thickness of the p-type ZnS _v Se _1-v layer 8 is 0.3 μm, for example.
m, N _A -N _D is, for example, ^{(2~5) × 10 17 cm -3} . The thickness of the p-type ZnSe contact layer 9 is, for example, 200.
nm, N _A -N _D is, for example, ^{(5~8) × 10 17 cm -3} . The thickness of the p-type ZnTe contact layer 11 is 10nm for example, N _A -N _D, for example 1 × 10 ¹⁹ c
m ^-3 .

The thickness of the n-type ZnSe buffer layer 2 is Zn
Since there is a slight lattice mismatch between Se and GaAs, this n mismatch is caused by this lattice mismatch.
In order to prevent dislocation from occurring during epitaxial growth of the ZnSe buffer layer 2 and each layer thereon, Z
It is selected to be sufficiently smaller than the critical film thickness of nSe (up to 100 nm), but in this embodiment, it is 33 nm, for example.

The p-type ZnS _v Se _1-v layer 8 is made of p-type Zn
_1-p Mg _p S _q Se _1-q second p added to cladding layer 7
P-type Zn _1-p Mg _p S _q S
The e _1-q clad layer 7 has a function of lattice matching, a function of a spacer layer for preventing a short circuit due to a solder crawling on a chip end surface when mounting a laser chip on a heat sink, and the like.

As described above, the p-type ZnS _v Se _1-v layer 8 constitutes the second p-type clad layer together with the p-type Zn _1-p Mg _p S _q Se _1-q clad layer 7 to provide the optical The confinement property and the carrier confinement property can be improved. The mobility of holes in ZnSSe is Zn
Since it is larger than that of MgSSe, the p-type clad layer is composed of only the _{p -} type Zn _1-p Mg _p S _q Se _1-q clad layer 7 when the total thickness of the p-type clad layer is the same. Compared with the case, the p-type clad layer is formed with p-type Zn.
_1-p Mg _p S _q Se _1-q clad layer 7 and p-type ZnS _v S
The p-type clad layer can be made lower in resistance when it is formed of the e _1-v layer 8. Since the resistance of the p-type cladding layer is reduced in this manner, the voltage drop due to the p-type cladding layer is reduced, which contributes to lowering the operating voltage of the semiconductor laser.

Further, the p-type ZnSe contact layer 9 is p-typed.
If the Zn _1-p Mg _{p Sq} Se _1-q cladding layer 7 is directly laminated, the crystallinity is likely to deteriorate due to the lattice mismatch between these layers, but the p-type Zn _1-p Mg _p
A p-type ZnS _v Se _1-v layer 8 which is lattice-matched with the S _q Se _1-q cladding layer 7 is laminated on the p-type ZnS _v Se layer.
_{Since the} p-type ZnSe contact layer 9 is laminated on the _1-v layer 8, the crystallinity of these p-type ZnS _v Se _1-v layer 8 and p-type ZnSe contact layer 9 can be improved. This contributes to the improvement of ohmic contact characteristics of the p-side electrode 13.

In addition to the above advantages, p-type ZnS _v Se _1-v
By providing the layer 8, the following advantages can also be obtained. That is, this p-type ZnS _v Se
_{When the 1-v} layer 8 is used as the second p-type clad layer, p-type Zn _1-p Mg _p S _q is not as easy to grow epitaxially as binary or ternary II-VI compound semiconductors.
The thickness of the Se _1-q clad layer 7 can be minimized, and the semiconductor laser can be manufactured accordingly.

The p-type ZnSe / ZnTe MQW layer 1 described above
0 is provided for the p-type ZnSe contact layer 9
And the p-type ZnTe contact layer 11 are directly joined,
A large discontinuity occurs in the valence band at the junction interface,
This is from the p-side electrode 13 to the p-type ZnTe contact layer 11
This is because it becomes a potential barrier for the holes injected into the substrate, so that this barrier is effectively eliminated.

That is, the carrier concentration in p-type ZnSe is typically about 5 × 10 ¹⁷ cm ^-3 , while the carrier concentration in p-type ZnTe can be 10 ¹⁹ cm ^-3 or more. is there. The discontinuity of the valence band at the p-type ZnSe / p-type ZnTe interface is about 0.8 eV. In the valence band of such a p-type ZnSe / p-type ZnTe junction, assuming that the junction is a step junction,
the p-type ZnSe side W = bending of (2εφ _T / qN _A) band across the width of the ^1/2 (1) occurs. Here, q is the absolute value of electron charge, ε is the dielectric constant of ZnSe, and φ _T is p.
Represents the discontinuous potential (about 0.8 eV) in the valence band at the ZnSe / p-type ZnTe interface.

At this time, the top of the valence band is p-type ZnSe.
FIG. 9 shows how it changes along the direction perpendicular to the / p-type ZnTe interface. However, p-type ZnS
The Fermi levels of e and p-type ZnTe are approximated to coincide with the top of the valence band. As shown in FIG. 9, in this case, the valence band of p-type ZnSe is bent downward toward p-type ZnTe. This downward convex valence band change acts as a potential barrier for holes injected into the p-type ZnSe / p-type ZnTe junction.

This problem is caused by the p-type ZnSe contact layer 9
And p-type ZnTe contact layer 11 between p-type ZnSe
This can be solved by providing the / ZnTeMQW layer 10. This p-type ZnSe / ZnTe MQW layer 10
Is designed as follows by making it possible to increase the ground quantum level E ₁ formed in the quantum well by reducing the width L _W of the quantum well.

In this case, the band bending generated over the width W from the p-type ZnSe / p-type ZnTe interface to the p-type ZnSe side is the distance x from the p-type ZnSe / p-type ZnTe interface.
It is given by the quadratic function φ (x) = φ _T {1- (x / W) ² } (2) in (FIG. 9). Therefore, p-type ZnSe / ZnTe MQW
The design of the layer 10 is based on the equation (2) so that the ground quantum level E ₁ formed in each of the quantum well layers made of p-type ZnTe has an energy at the top of the valence band of p-type ZnSe and p-type ZnTe. Can be performed by gradually changing L _W so as to be equal to each other and equal to each other.

FIG. 10 shows the p-type ZnSe / ZnTe MQW.
A design example in which the width L _B of the p-type ZnSe barrier layer in the layer 10 is constant (for example, 2 nm) is shown. As shown in FIG. 10, in this case, the width L _W of the seven quantum wells in total is set so that the ground quantum level E ₁ thereof matches the Fermi level of p-type ZnSe and p-type ZnTe. It is gradually increased from the ZnSe contact layer 9 to the p-type ZnTe contact layer 11.

In FIG. 10, the holes injected into the p-type ZnTe are resonantly tunneled through the ground quantum level E ₁ formed in each quantum well of the p-type ZnSe / ZnTe MQW layer 10 to the p-type ZnSe side. The potential barrier at the p-type ZnSe / p-type ZnTe interface effectively disappears. Therefore, according to the semiconductor laser of this embodiment, good voltage-current characteristics can be obtained, and the operating voltage can be lowered.

In designing the width L _W of the quantum well, strictly speaking, since the levels of the respective quantum wells are coupled to each other, it is necessary to consider their interaction. Although the effect of strain due to the lattice mismatch between the well and the barrier layer must be taken into consideration, it is theoretically possible to set the quantum level of the multiple quantum well flat as shown in FIG.

Next, a method of manufacturing the semiconductor laser according to this embodiment having the above-mentioned structure will be described.

In order to manufacture the semiconductor laser according to this embodiment, first, for example, by the molecular beam epitaxy (MBE) method at a temperature in the range of 250 to 300 ° C., specifically at 295 ° C., for example, n-type GaAs. On the substrate 1, an n-type ZnSe buffer layer 2 and an n-type Zn _1-p Mg _p S
_q Se _1-q clad layer 3, n-type ZnS _u Se _1-u optical waveguide layer 4, i-type Zn _1-z Cd _z Se quantum well layer active layer 5, p-type ZnS _u Se _1-u optical waveguide Layer 6, p-type Zn _1-p
Mg _p S _q Se _1-q clad layer 7, p-type ZnS _v Se
_1-v layer 8, p-type ZnSe contact layer 9, p-type ZnSe
/ ZnTe MQW layer 10 and p-type ZnTe contact layer 11 are sequentially epitaxially grown. In this case, these layers can be epitaxially grown with good crystallinity, and therefore deterioration such as reduction of the light output of the semiconductor laser can be suppressed and high reliability can be obtained.

In the above epitaxial growth by the MBE method, for example, a Zn raw material has a purity of 99.99.
99% of Zn is used, and the purity of Mg is 99.9%.
Of Mg and 99.9999% Zn as the S raw material
S is used, and as a Se raw material, S having a purity of 99.9999%
e is used. In addition, the n-type ZnSe buffer layer 2 and the n-type Z
n _1-p Mg _p S _q Se _1-q cladding layer 3 and n-type Zn
The doping of Cl as a donor impurity of the S _u Se _1-u optical waveguide layer 4 is performed by, for example, ZnCl 2 having a purity of 99.9999%.
₂ is used as a dopant. On the other hand, p-type ZnS _u
Se _1-u optical waveguide layer 6, p-type Zn _1-p Mg _p S _q Se _1-q
Cladding layer 7, p-type ZnS _v Se _1-v layer 8, p-type ZnS
e contact layer 9, p-type ZnSe / ZnTe MQW layer 1
Doping of N as 0 and the p-type ZnTe contact layer 11 as an acceptor impurity is performed by irradiating N ₂ plasma generated by electron cyclotron resonance (ECR), for example.

Next, a stripe-shaped resist pattern (not shown) having a predetermined width is formed on the p-type ZnTe contact layer 11, and the p-type ZnS _v Se _1-v layer 8 is formed using this resist pattern as a mask. Etching is performed by a wet etching method in the middle of the thickness direction. As a result, the upper layer portion of the p _- type ZnS _v Se _1-v layer 8 and the p-type ZnSe
Contact layer 9, p-type ZnSe / ZnTe MQW layer 10
The p-type ZnTe contact layer 11 is patterned into a stripe shape.

Next, Al ₂ where a resist pattern on the entire surface a thickness of leaving used for etching described above was vacuum-deposited an Al ₂ O ₃ film of 300 nm, the resist pattern was formed thereon It is removed together with the O ₃ film (lift-off). As a result, Al ₂ O is formed only on the p-type ZnS _v Se _1-v layer 8 other than the stripe portion.
_The insulating layer 12 composed of _three films is formed.

Next, a Pd film, a Pt film, and an Au film are sequentially vacuum-deposited on the entire surface of the stripe-shaped p-type ZnTe contact layer 11 and the insulating layer 12 to form a p-side electrode 13 composed of a Pd / Pt / Au electrode. Then, heat treatment is performed as necessary to bring the p-side electrode 13 into ohmic contact with the p-type ZnTe contact layer 11. On the other hand, on the back surface of the n-type GaAs substrate 1, an n-side electrode 1 such as an In electrode
4 is formed.

Next, the n-type GaAs substrate 1 having the laser structure formed as described above is cleaved into a bar shape to form both resonator end faces, and then Al is formed on the front end face by, for example, a vacuum deposition method. _A multilayer film composed of the ₂ O ₃ film 15 and the Si film 16 is formed, and Al ₂ O ₃ is formed on the rear end face.
A multilayer film is formed by repeating the film 15 and the Si film 16 for two cycles. After the end face coating is applied in this manner, the bar is cleaved to form chips, and packaging is performed.

As described above, according to the semiconductor laser of this embodiment, the Mg composition ratio p of the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 3 is 0.10 <p ≦ 0. 20,
For example, by setting it to 0.15, i-type Zn _1-z C
Active layer 5 consisting of d _z Se quantum well layer and n-type Zn _1-p M
The difference ΔE _g of the band gap E _{g with} the g _p S _q Se _1-q cladding layer 3 can be made sufficiently large, for example, 0.30 eV. Moreover, the active layer 5 composed of the i-type Zn _1-z Cd _z Se quantum well layer and the p-type Zn _1-p Mg _p S _q Se
Difference in band gap E _g between _1-q clad layer 7 ΔE
_g can also be made sufficiently large, for example, 0.40 eV. Therefore, good carrier confinement characteristics and optical confinement characteristics can be obtained. In addition, n-type Zn _1-p M
Since the ionization energy of Cl, which is a donor impurity in the g _p S _q Se _1-q cladding layer 3, can be suppressed to be small, it is possible to prevent a decrease in luminous efficiency that occurs when the ionization energy of Cl is large. By these, the threshold current density of the semiconductor laser can be reduced.

Since the activation rate of Cl in the n-type Zn _1-p Mg _p S _q Se _1-q cladding layer 3 can be made sufficiently large, this n-type Zn _1-p Mg _p S _q It is possible to reduce the density of defects such as non-radiative centers due to Cl that has not been activated in the Se _{1 -q} cladding layer 3. Further, the layers constituting this semiconductor laser are substantially lattice-matched with each other and also with the n-type GaAs substrate 1, so that dislocations are generated in these layers during epitaxial growth of these layers. Can be prevented, and the crystallinity of the growth layer can be improved. As a result, it is possible to prevent the semiconductor laser from deteriorating due to the inherent defects, and it is possible to extend the life of the semiconductor laser.

As described above, Zn was used as the material for the cladding layer.
_{It is} possible to realize a semiconductor laser using _1-p Mg _p S _q Se _1-q, which has a low threshold current density and a long lifetime and can oscillate at about 480 nm. Furthermore, according to this semiconductor laser, stable room temperature continuous oscillation can be realized.

Although one embodiment of the present invention has been specifically described above, the present invention is not limited to the above embodiment, and various modifications can be made based on the technical idea of the present invention. .

For example, the n-type ZnS _u Se _1-u optical waveguide layer 4 and the p-type ZnS used in the above-mentioned embodiments are used.
Instead of the _u Se _1-u optical waveguide layer 6, an n-type ZnSe optical waveguide layer and a p-type ZnSe optical waveguide layer may be used.

Further, in the above-mentioned embodiment, p-type Zn
S _u Se _1-u optical waveguide layer 6, p-type Zn _1-p Mg _p S _q Se
_1-q clad layer 7, p-type ZnS _v Se _1-v layer 8, p-type Z
nSe contact layer 9, p-type ZnSe / ZnTe MQW
The doping of N as an acceptor impurity in the layer 10 and the p-type ZnTe contact layer 11 is performed by irradiating N ₂ plasma generated by ECR. The N doping is excited by high-frequency plasma, for example. Alternatively, it may be performed by irradiating with N ₂ .

Further, in the above embodiment, n-type Zn
Cl is used as a donor impurity for the Se buffer layer 2, the n-type Zn _1-p Mg _{p Sq} Se _1-q cladding layer 3, and the n-type ZnS _u Se _1-u optical waveguide layer 4. May use I, for example.

Further, in the above-mentioned embodiment, the epitaxial growth of each layer constituting the semiconductor laser is carried out by the MBE method, but this epitaxial growth may be carried out by the metal organic chemical vapor deposition (MOCVD) method.

Further, i-type Zn in the above-mentioned embodiment
Instead of the active layer 5 composed of the _1-z Cd _z Se quantum well layer, an active layer having a multiple quantum well structure including a plurality of quantum well layers composed of i-type Zn _1-z Cd _z Se may be used.

Further, in the above-mentioned embodiments, the case where the present invention is applied to the semiconductor laser having the SCH structure has been described, but the present invention is DH (Double Heteros).
It may be applied to a semiconductor laser having a tructure) structure.

[0069]

As described above, according to the present invention, the Mg composition ratio of the ZnMgSSe-based compound semiconductor forming the n-type cladding layer is larger than 0.10.
Since it is 20 or less, Zn is used as a material for the cladding layer.
It is possible to realize a semiconductor light emitting device using a MgSSe-based compound semiconductor and having a low threshold current density and a long life.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the band gap E _g of Cl-doped n-type ZnMgSSe and the ionization energy E _d of Cl as a donor impurity.

FIG. 2 is a graph showing the relationship between the Mg composition of Cl-doped n-type ZnMgSSe and the ionization energy E _d of Cl as a donor impurity.

3 is a graph showing the relationship between the band gap of the Cl-doped n type ZnMgSSe E _g and the effective donor concentration N _D -N _A and carrier concentration.

4 is a graph showing the relationship between the Cl-doped n-type Mg composition and effective donor concentration N _D -N _A and the carrier concentration of ZnMgSSe.

5 is a graph showing the relationship between the Cl-doped n-type band gap of ZnMgSSe E _g and activation ratio _{N D -N A / [Cl]} .

6 is a graph showing the relationship between the Cl-doped n type ZnMgSSe the Mg composition and activation ratio _{N D -N A / [Cl]} .

FIG. 7 is a cross-sectional view perpendicular to the cavity length direction of a semiconductor laser according to an embodiment of the present invention.

FIG. 8 is a sectional view parallel to the cavity length direction of the semiconductor laser according to the embodiment of the present invention.

FIG. 9 is an energy band diagram showing a valence band near a p-type ZnSe / p-type ZnTe interface.

FIG. 10 is an energy band diagram showing a design example of a p-type ZnSe / ZnTe MQW layer in a semiconductor laser according to an example of the present invention.

[Explanation of symbols]

1 n-type GaAs substrate 2 n-type ZnSe buffer layer 3 n-type _{Zn 1-p Mg p S q} Se 1-q cladding layer 4 n-type ZnS _u Se _1-u optical waveguide layer 5 active layer 6 p-type ZnS _u Se _{1 -u} optical waveguide layer 7 p-type _{Zn 1-p Mg p S q} Se 1-q cladding layer 8 p-type ZnS _v Se _1-v layer 9 p-type ZnSe contact layer 10 p-type ZnSe / ZnTe MQW layer 11 p-type ZnTe contact Layer 13 p-side electrode 14 n-side electrode

Claims (7)

[Claims] 1. A semiconductor light emitting device having a structure in which a compound semiconductor substrate is used and an active layer made of a II-VI group compound semiconductor is sandwiched by an n-type clad layer and a p-type clad layer made of ZnMgSSe compound semiconductor on both sides. The Mg composition ratio of the ZnMgSSe-based compound semiconductor forming the n-type cladding layer is larger than 0.10.
A semiconductor light-emitting device characterized by being 20 or less. 2. ZnMg constituting the n-type cladding layer
2. The semiconductor light emitting device according to claim 1, wherein the Mg composition ratio of the SSe-based compound semiconductor is greater than 0.10 and 0.18 or less. 3. The lattice mismatch between the compound semiconductor substrate and the ZnMgSSe-based compound semiconductor forming the n-type cladding layer is within 0.25%.
The semiconductor light-emitting device as described above. 4. ZnMg constituting the n-type cladding layer
The semiconductor light emitting device according to claim 1, wherein the band gap of the SSe-based compound semiconductor at a liquid nitrogen temperature is 3.10 eV or less. 5. The semiconductor light emitting device according to claim 1, wherein the active layer is made of a ZnCdSe based compound semiconductor, a ZnSe based compound semiconductor, a ZnSSe based compound semiconductor or a ZnMgSSe based compound semiconductor. 6. A first optical waveguide layer and a second optical waveguide layer are provided between the active layer and the n-type clad layer and the p-type clad layer, respectively, and the first optical waveguide layer and the second optical waveguide layer are provided. The semiconductor light emitting device according to claim 1, wherein the second optical waveguide layer is made of a ZnSSe-based compound semiconductor or a ZnSe-based compound semiconductor. 7. The semiconductor light emitting device according to claim 1, wherein the compound semiconductor substrate is a GaAs substrate.