JPH09289353A - Semiconductor light emitting device and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability of a II-VI compound semiconductor light emitting device. SOLUTION: An n-type GaAs layer 102, an n-type ZnSe buffer layer 103, an n-type ZnMgSSe clad layer 104, a strain multiple quantum well structure 107 composed of four Zn0.8Cd0.2Se well layers 105 and five ZnS0.2Se0.8 barrier layers 106, a p-type ZnMgSSe clad layer 108, and a p-type ZnSe contact layer 109 are stacked on a GaAs substrate 101. As the ZnSSe barrier layer 106 having an S composition ratio of 0.2 is used, a tensile strain acting on the barrier layer compensates a compression strain acting on the well layer. Therefore, the strain acting on the strain multiple quantum well structure 107 and the vicinity thereof is offset almost perfectly, thereby providing a non-strain state as a whole. Thus, generation of and increase in defects in the well layers 105 are restrained, thus enabling improvement in reliability of the device.

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 a method for manufacturing the same, and more particularly to a II-VI compound semiconductor laser or a light emitting diode that emits light in a blue-green region, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In order to improve the recording density of an optical disk, the resolution of a laser printer, or the application to an optical measuring device, a medical device, etc., a semiconductor light emitting device capable of emitting light in a blue-green region, particularly a semiconductor laser, is developed. Is being actively conducted. As a material capable of emitting light in such a short wavelength region, a II-VI group compound semiconductor is promising.

A conventional semiconductor light emitting device using a II-VI group compound semiconductor and a method for manufacturing the same are described in, for example, J. Va.
c. Sci. Technol. A 13 (1995) p.683. GaAs buffer layer, Zn on n-type GaAs substrate
Through the Se buffer layer and the ZnSSe buffer layer,
ZnCdSe quantum well active layer, ZnSSe optical guide layer,
A separate confinement heterostructure consisting of a ZnMgSSe cladding layer is formed. As a contact to the p-type electrode, a p-type ZnSe cap layer, p-type ZnSe / ZnTe
A multiple quantum well layer and a ZnTe contact layer are sequentially stacked. The molecular beam epitaxial growth method is used for manufacturing the above semiconductor laminated structure. Then, after etching the ZnTe contact layer in a mesa stripe shape, current confinement is performed by the insulating layer to obtain a gain waveguide type laser element. For the p-side electrode, Pd / Pt / Au, n
In is used for each of the side electrodes.

With respect to such a device, room temperature continuous oscillation at a wavelength of 490 to 524 nm was achieved depending on the Cd composition ratio of the active layer and the quantum effect, and a device life of 9 minutes was reported for a device having 3 wells. .

[0005]

However, the above-mentioned II-VI group compound semiconductor light-emitting device has 10 ⁴ to 10 ⁵
Since stacking faults exist at a density of cm ^−2, dislocations grow from the stacking faults in the active layer where current is injected during operation, which causes a decrease in emission intensity and stop of laser oscillation, resulting in a short device life. There is a problem. Even if it is possible to suppress the occurrence of stacking faults and eliminate stacking faults in the current injection region, crystal defects are generated and multiply in the active layer during operation, so the reliability of the device is low and limited. . The cause of this is not clear, but the presence of compressive strain due to the fact that the lattice constant of the ZnCdSe active layer is larger than the lattice constants of the substrate and other semiconductor layers, or incomplete crystal quality at the interface of this mixed crystal quantum well. However, it is considered to be the driving force for the growth of crystal defects. When a multiple quantum well structure is adopted for the active layer, the total thickness of the ZnCdSe layer and the number of quantum well interfaces increase, so the above-mentioned problem becomes remarkable.

As a problem peculiar to II-VI group compound semiconductors, AlGaAs, AlGaInP, InGa
I has already been put to practical use as a semiconductor light emitting device such as AsP.
Compared with II-V group compound semiconductors, there is a problem that the covalent bond between constituent atoms is small and crystal defects are likely to occur.

Therefore, an object of the present invention is to suppress the generation and multiplication of crystal defects generated in the active layer during operation, improve the crystal quality of the active layer, and improve the reliability of the device. And to provide a manufacturing method thereof.

[0008]

In order to achieve the above object, a semiconductor light emitting device according to a first aspect of the present invention is a semiconductor light emitting device made of a II-VI compound semiconductor having a strained multiple quantum well structure. The barrier layer has a lattice strain opposite to that of the well layer.

In the above structure, the semiconductor light emitting device is made of a II-VI group compound semiconductor lattice-matched to the GaAs substrate or the ZnSe substrate, and the well layer is ZnCdS.
It is preferable that the barrier layer is made of e and the barrier layer has a composition having tensile strain.

The semiconductor light emitting device according to the second aspect of the present invention is a semiconductor light emitting device made of a II-VI group compound semiconductor having a multiple quantum well structure, and the well layer and the barrier layer are at least three or more kinds of elements. And a compound intermediate layer between the well layer and the barrier layer.

In the above structure, the semiconductor light emitting device is made of a II-VI group compound semiconductor lattice-matched to the GaAs substrate or the ZnSe substrate, and the well layer is ZnCdS.
e, and the barrier layer is ZnSSe or ZnMgSS
Preferably, the intermediate layer is made of ZnSe and the intermediate layer is made of ZnSe.

The semiconductor light emitting device according to the combination of the first and second aspects of the present invention is a semiconductor light emitting device made of a II-VI group compound semiconductor having a strained multiple quantum well structure, and has a lattice strain of well layers. Is provided with a barrier layer having an inverse lattice strain, the well layer and the barrier layer are made of a mixed crystal composed of at least three kinds of elements, and the compound is provided between the well layer and the barrier layer. It has an intermediate layer.

In the above structure, the well layer is a ZnCdS semiconductor light emitting device made of a II-VI group compound semiconductor lattice-matched to a GaAs substrate or a ZnSe substrate.
It is preferable that the barrier layer is made of e, the barrier layer is made of ZnSSe or ZnMgSSe having tensile strain, and the intermediate layer provided between the well layer and the barrier layer is made of ZnSe.

A semiconductor light emitting device according to a third aspect of the present invention is a semiconductor light emitting device made of a II-VI group compound semiconductor provided with an optical guide layer and an active layer having a lattice strain, and at least one of the optical guide layers. The part is composed of a composition having a lattice strain opposite to that of the active layer.

In the above structure, the semiconductor light emitting device is made of a II-VI group compound semiconductor lattice-matched to the GaAs substrate or the ZnSe substrate, and the active layer is ZnCd.
It is preferable that the light guide layer is made of Se and at least a part of the light guide layer has a composition having tensile strain.

A semiconductor light emitting device according to a fourth aspect of the present invention is a semiconductor light emitting device including a single quantum well structure and an optical guide layer II.
A semiconductor light emitting device made of a group VI compound semiconductor, wherein the well layer and the light guide layer are made of a mixed crystal composed of at least three kinds of elements, and the compound is provided between the well layer and the light guide layer. It has an intermediate layer.

In the above structure, the semiconductor light emitting device is made of a II-VI group compound semiconductor lattice-matched with a GaAs substrate or a ZnSe substrate, and the well layer is ZnCd.
Made of Se, and the light guide layer is ZnSSe or ZnM
Preferably, it is made of gSSe and the intermediate layer is made of ZnSe.

A semiconductor light emitting device according to the combination of the third and fourth aspects of the present invention is a semiconductor light emitting device made of a II-VI group compound semiconductor provided with a strained single quantum well structure and a light guide layer. The layer and the light guide layer are made of a mixed crystal composed of at least three kinds of elements, and an intermediate layer made of a compound is provided between the well layer and the light guide layer, and at least a part of the light guide layer. However, it has a composition having a lattice strain opposite to that of the well layer.

In the above structure, the semiconductor light emitting device is made of a II-VI group compound semiconductor lattice-matched to the GaAs substrate or the ZnSe substrate, and the well layer is ZnCd.
Se, and at least a part of the optical guide layer is made of ZnSSe or ZnMgSSe having tensile strain,
The intermediate layer is preferably made of ZnSe.

The semiconductor light-emitting device according to the fifth aspect of the present invention is a semiconductor light-emitting device made of a II-VI group compound semiconductor, which has a lattice constant of the substrate and the lattice constant in the clad layer closer to the substrate than the active layer. At least 1 different semiconductor layer
Layers, and the thickness of the semiconductor layer is smaller than the critical film thickness for the substrate.

In the above structure, the cladding layer is ZnM.
gSSe, wherein the semiconductor layer is ZnS, ZnSe,
It is preferably made of ZnSSe, ZnMgS or ZnMgSe.

A semiconductor light emitting device according to a sixth aspect of the present invention is a semiconductor light emitting device made of a II-VI group compound semiconductor, wherein a strained superlattice layer is provided in the clad layer closer to the substrate than the active layer. It is what has been.

In the above structure, the cladding layer is ZnM.
gSSe, the strained superlattice layer is Zn, Mg, Cd,
Consists of elements selected from S, Se and Te
It is preferably composed of two or more kinds of compounds or mixed crystals.

A semiconductor light emitting device according to a seventh aspect of the present invention is an I-type semiconductor device formed on a III-V group compound semiconductor substrate.
A semiconductor light emitting device made of a group I-VI compound semiconductor, comprising a group II-VI compound semiconductor layer substantially free of n-type and p-type impurities, directly above the substrate surface, and The layer thickness is 10 molecular layers or less.

In the above-mentioned structure, I containing 1 × 10 18 cm −3 or more of the impurities is formed on the II-VI group compound semiconductor layer which is substantially free of n-type and p-type impurities.
It is preferable that I-VI group compound semiconductor layers are laminated.

In the above structure, it is preferable that the III-V group compound semiconductor substrate is a GaAs substrate and the II-VI group compound semiconductor layer substantially free of n-type and p-type impurities is ZnSe.

A method for manufacturing a semiconductor light emitting device according to an eighth aspect of the present invention is a method for manufacturing a semiconductor light emitting device made of a II-VI compound semiconductor formed on a III-V compound semiconductor substrate. II- laminated on the substrate
The temperature for growing at least a part of the VI compound semiconductor buffer layer is higher than the growth temperature of the semiconductor layer stacked thereon.

In the above structure, the III-V compound semiconductor substrate is preferably a GaAs substrate and the II-VI compound semiconductor buffer layer is preferably ZnSe.

In the above structure, the growth of the semiconductor layer is interrupted after the growth of the buffer layer or during the growth thereof,
It is preferable to lower the growth temperature. Alternatively, it is preferable that the growth temperature of the buffer layer is lowered during the growth so that the growth of the semiconductor layer is not interrupted.

A method for manufacturing a semiconductor light emitting device according to a ninth aspect of the present invention is a method for manufacturing a semiconductor light emitting device made of a II-VI group compound semiconductor, wherein the temperature for growing a semiconductor layer including at least an active layer is: It is higher than the growth temperature of the semiconductor layers other than the semiconductor layer.

In the above structure, it is preferable that the temperature at which the active layer and the light guide layer are grown is higher than the growth temperature of the semiconductor layer other than the active layer and the light guide layer.

In the above structure, the growth of the semiconductor layer is interrupted before and after the growth of the active layer and the light guide layer,
It is preferable to change the growth temperature. Alternatively, it is preferable not to interrupt the growth of the semiconductor layer by changing the growth temperature during the growth of the light guide layer.

[0033]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor light emitting device and a method of manufacturing the same according to the present invention will be described in detail below.

(Embodiment 1) FIG. 1 is a structural sectional view schematically showing a first embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a strained multiple quantum well structure.

As shown in FIG. 1, an n-type GaAs substrate 10
N-type GaAs buffer layer 102 and n-type ZnSe
Buffer layer 103, n-type ZnMgSSe cladding layer 10
4, strained multiple quantum well structure 107 composed of ZnCdSe well layer 105 and ZnSSe barrier layer 106, p-type ZnM
The gSSe clad layer 108 and the p-type ZnSe contact layer 109 are sequentially stacked.

In this case, the upper portion of the p-type ZnMgSSe cladding layer 108 and the p-type ZnSe contact layer 109 are etched in a mesa stripe shape. The width of this mesa stripe portion is, for example, 5 μm. Further, an insulating layer 110 is formed on the p-type ZnMgSSe cladding layer 108 in the portion other than the above-mentioned mesa stripe portion. Then, the p-type ZnSe contact layer 109 and the insulating layer 1
A p-type electrode 111 is formed on the layer 10. As the p-type electrode 111, for example, a Pd / Au electrode in which a Pd film having a thickness of 10 nm and an Au film having a thickness of 300 nm are sequentially stacked is used.

On the other hand, on the back surface of the n-type GaAs substrate 101, an n-type electrode 112 such as an In electrode is formed. Although the structure shown in FIG. 1 is a gain-guiding type, it can be a single-mode operation index-guiding structure by appropriately selecting the width and height of the mesa stripe and the refractive index of the insulating layer. .

As a substrate of the II-VI group compound semiconductor light emitting device, a III-V group compound semiconductor such as GaAs, InP, GaP, etc., a IV group semiconductor such as Si, Ge or Zn.
II-VI group compound semiconductors such as Se and CdS may be mentioned. II-V laminated on the substrate, depending on the choice of substrate
The composition of the Group I compound semiconductor is chosen to be lattice matched to the substrate. In the case of GaAs, GaP, Si, Ge and ZnSe substrates, the cladding layer is, for example, ZnMgSSe.
The system or ZnMgBeSe system is selected. In the case of an InP substrate, for example, a ZnMgCdSe-based or Z-based cladding layer is used.
The nMgSeTe system is chosen. The conductivity type of the substrate may be either n-type or p-type.
It may be semi-insulating. In the present embodiment, for example, the n-type GaAs substrate 101 having the (100) plane orientation is used. Regarding the substrate plane orientation, from (100) plane to (11
1) A surface inclined in the A or (111) B direction may be used. For example, a (511) B plane inclined by 15.8 degrees in the (111) B direction can be used.

The n-type GaAs buffer layer 102 and the n-type ZnSe buffer layer 103 flatten the surface at the level of atomic arrangement, reduce the density of crystal defects of the II-VI group compound semiconductor stacked thereon, and It is provided to obtain quality crystals. In particular, the n-type ZnSe buffer layer 103 is
In the initial stage of the growth of the II-VI group compound semiconductor, S and Mg directly adhere to the GaAs substrate to generate crystal defects,
It is provided to prevent deterioration of crystal quality. The thickness of the n-type GaAs buffer layer 102 is 0.3 μm, the effective donor density is 2 × 10 18 cm −3, and Si is used as the n-type impurity, for example. Moreover, since ZnSe has a lattice constant of 0.56693 nm and has a lattice mismatch of + 0.28% with respect to GaAs, the critical film thickness is 150.
It is about nm. Therefore, the n-type ZnSe buffer layer 1
The thickness of 03 is selected to be 30 nm, for example. In addition, n-type Z
The effective donor density of the nSe buffer layer 103 is 7 × 10 ¹⁷
cm ⁻³ , and for example, Cl is used as the n-type impurity.

The composition of the n-type ZnMgSSe cladding layer 104 and the p-type ZnMgSSe cladding layer 108 is Mg composition ratio 0.1 and S composition ratio 0.2, and ZnMgSSe having this composition lattice-matches with GaAs. The band gap at room temperature is 2.86 eV. ZnMgS
Se has a band gap of 2.7 eV to 3.1 e while being lattice-matched with GaAs by selecting its composition.
It can be varied between about V. n-type ZnMgS
The Se clad layer 104 has a thickness of 1.2 μm and an effective donor density of 5 × 10 ¹⁷ cm ⁻³ .
For example, Cl is used. The p-type ZnMgSSe cladding layer 108 has a thickness of 1.1 μm and an effective acceptor density of 2 × 10 ¹⁷ cm ⁻³ , and N is used as the p-type impurity, for example.

The strained multiple quantum well structure 107 has four layers of ZnO.
It is composed of an 8Cd0.2Se well layer (thickness 4 nm each) 105 and five layers of ZnS0.2Se0.8 barrier layer (thickness 8 nm each) 106. The band gap of the well layer 105 at room temperature (27 ° C.) is 2.48 eV. FIG. 2 is a diagram schematically showing lattice irregularities around the strained multiple quantum well structure 107.
As shown in FIG. 2, the lattice constant of Zn0.8Cd0.2Se is 0.5745 nm, and the lattice constant of GaAs is 0.56.
There is a compressive strain in the well layer 105 due to the lattice mismatch of + 1.6% with respect to 533 nm. In addition, ZnS
The lattice constant of 0.2Se0.8 is 0.56173 nm, and G
Since there is a lattice mismatch of −0.6% with respect to aAs, tensile strain exists in the barrier layer 106.

For the active layer, ZnSe, ZnSSe, Z
When nCdSe or the like is used and the substrate is GaAs, Zn
Se and ZnCdSe are subject to compressive strain, and ZnSSe is subject to tensile strain. When ZnSe or ZnCdSe is used for the active layer, ZnSS having tensile strain is used for the barrier layer.
e or ZnMgSSe or the like is used.

In order to prevent the formation of impurity levels in the active layer, it is preferable to add neither n-type impurities nor p-type impurities to the well layer and the barrier layer.

The thickness of the p-type ZnSe contact layer 109 is selected to be thinner than the critical film thickness for GaAs as described above, and is, for example, 80 nm. The effective acceptor density of the p-type ZnSe contact layer 109 is 9
× 10 ¹⁷ cm ⁻³ , and the p-type impurity is, for example, N.
Is used.

The insulating layer 110 is made of ZnS, Al2O3, S
It is formed of iO2 or ZnO. ZnO is preferable from the viewpoints of adhesion and thermal conductivity to II-VI group compound semiconductors such as ZnMgSSe.

The operation and effect of the semiconductor laser configured as described above will be described. The critical thickness of Zn0.8Cd0.2Se for GaAs is considered to be about 15 to 20 nm. In the present embodiment, the total thickness of the Zn0.8Cd0.2Se well layer 105 is 16 nm, which is about the same as the critical thickness. At this time, tentatively, as the barrier layer 106, Zn having an S composition ratio of 0.06 which lattice-matches GaAs as in the conventional case is used.
When SSe is used, the total sum of compressive strains applied to the quantum well structure and its vicinity becomes large, and crystal defects are easily generated and proliferated in this region by current injection during operation, and as a result, the device life is shortened. In this embodiment, since the ZnSSe barrier layer 106 having an S composition ratio of 0.2 is used, the tensile strain applied to the barrier layer compensates for the compressive strain applied to the well layer. Almost all distortions in the vicinity are canceled out, and the total sum is close to a distortion-free state. Therefore, the well layer 105
Occurrence and proliferation of defects are suppressed, and as a result, reliability of the device can be improved.

Regarding the degree of strain compensation, it is not always necessary to have a total strain-free state as in the present embodiment, and a compression strain or a tensile strain may exist as a total. However, also in this case, each layer thickness of the strained multiple quantum well structure is designed to be thinner than the critical film thickness.

Next, a method of manufacturing the semiconductor laser configured as described above will be described. In the present embodiment, the semiconductor laminated structure is formed using the molecular beam epitaxial growth (MBE) method, but metal organic vapor phase epitaxy (MO) is used.
A similar structure can be formed by using the VPE method. The manufacturing method by the MBE method will be described below.

First, MB is formed on the n-type GaAs substrate 101.
The n-type GaAs buffer layer 102, the n-type ZnSe buffer layer 103, and the n-type ZnMgSSe cladding layer 10 are formed by the E method.
4, strained multiple quantum well structure 107 composed of ZnCdSe well layer 105 and ZnSSe barrier layer 106, p-type ZnM
The gSSe cladding layer 108 and the p-type ZnSe contact layer 109 are sequentially epitaxially grown. n-type GaAs
The growth of the buffer layer 102 is based on the n-type ZnSe buffer layer 1
It is performed in a growth chamber different from the growth chamber in which the semiconductor layer above 03 is grown. That is, an M including a growth chamber for III-V compound semiconductors and a growth chamber for II-VI compound semiconductors.
A BE device is used. A single crystal semiconductor layer is epitaxially grown by heating and evaporating a raw material in a Knudsen cell to form a molecular beam in a high-vacuum growth chamber of about 10 ⁻¹⁰ Torr and irradiating the single crystal semiconductor layer on the substrate.

Metal Ga, As, and Si as an n-type impurity material are used as a material for growing the n-type GaAs buffer layer 102. Moreover, for example, polycrystalline compounds ZnSe, ZnS, and metallic Mg are used as raw materials for II-VI group compound semiconductor growth. At this time, as an n-type impurity, for example, C
When 1 is used, ZnCl2 is used as a raw material. When N, for example, is used as the p-type impurity, active nitrogen generated by radio frequency (RF) plasma discharge or electron cyclotron resonance (ECR) plasma discharge is applied to the growing surface.

The substrate temperature during crystal growth is 580 to 620 ° C. for the n-type GaAs buffer layer 102, II-
The temperature of the Group VI compound semiconductor layer is preferably maintained at 260 to 330 ° C, for example, 290 ° C. The growth rate is preferably 0.7 to 1.5 μm / h for the n-type GaAs buffer layer 102, for example 1.0 μm.
/ H, and is preferably 0.4 to 3.0 μm / h with respect to the II-VI group compound semiconductor layer, for example, 0.5 to
0.8 μm / h.

The molecular beam intensity is usually controlled by controlling the cell temperature or the opening of the cell shutter or needle valve. In order to grow a semiconductor laminated structure requiring a plurality of molecular beam intensities for one raw material, a plurality of cells are prepared for one raw material, or control is performed by either of the above methods. From the standpoint of device simplicity,
It is preferable to obtain a plurality of molecular beam intensities by changing the cell temperature in one cell for one raw material, but there is a problem in growing such a semiconductor laminated structure. That is, when the molecular beam intensity is changed continuously, growth is not interrupted, but the growth conditions to be controlled become complicated, and when it is changed discontinuously, the growth is interrupted until the molecular beam intensity stabilizes. There are merits and demerits that it requires.

However, the semiconductor laminated structure and its composition shown in FIG. 1 are also advantageous from the viewpoints of simplicity and reproducibility of the above-described crystal growth method and apparatus. That is, the S composition ratio of the ZnMgSSe cladding layer and the ZnSSe
Since the S composition ratio of the barrier layer is the same, it is not necessary to change the molecular beam intensity of ZnS during the growth. Therefore, only one cell for the ZnS raw material is sufficient, and the II-VI group compound semiconductor layer can be continuously formed without interrupting the growth.

The wafer having a semiconductor laminated structure obtained by the above epitaxial growth is processed into a gain waveguide type laser device. That is, using a striped resist pattern having a width of, for example, 5 μm as a mask, the p-type ZnMgSSe cladding layer 108 is partially etched to form a mesa stripe. For the etching, for example, an etching solution in which a saturated aqueous solution of potassium dichromate and concentrated sulfuric acid are mixed at a volume ratio of 3: 2 is used. Subsequently, ZnO is used as the insulating film 110.
By, for example, sputtering deposition and lift-off to obtain p
The mold contact layer 109 is exposed. Then, for example, Pd and Au are sequentially vacuum-deposited on the entire surface of the wafer to form a p-type electrode 111.
And On the other hand, In is vacuum-deposited on the back surface of the n-type GaAs substrate 101 to form the n-type electrode 112.

This wafer is cleaved so that the resonator length is, for example, 700 μm, and both end faces are not coated,
For example, it is separated into chips having a width of 400 μm and mounted on a heat sink made of copper by junction down.

Finally, the results of evaluating the operating characteristics of this semiconductor laser device by continuously injecting a current at room temperature will be described. The oscillation wavelength is about 506 nm, the threshold current is 59 mA, the threshold current density is 1.7 kA / cm ² ,
The external differential quantum efficiency is 67%, and the applied voltage at the start of laser oscillation is about 14V. Also, the output at 20 ° C is 1m.
The device operating life at W is 1.1 hours.

On the other hand, for comparison, GaAs is used as a barrier layer.
When a semiconductor laser device using ZnSSe having an S composition ratio of 0.06 that is lattice-matched with was operated, no significant difference was observed in the initial laser oscillation characteristics, but the device operating life was about 2 minutes. In the semiconductor laser of this structure, the total sum of compressive strains applied to the quantum well structure and its vicinity is large, so it is considered that crystal defects are easily generated and propagate in this region by current injection, and as a result, the device life is shortened. .

From the above, according to the present embodiment,
The reliability of the II-VI group compound semiconductor laser device can be improved.

(Second Embodiment) FIG. 3 is a structural sectional view schematically showing a second embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a multiple quantum well structure.

As shown in FIG. 3, an n-type GaAs substrate 30 is provided.
N-type GaAs buffer layer 302 and n-type ZnSe on
Buffer layer 303, n-type ZnMgSSe cladding layer 30
4, ZnCdSe well layer 305 and ZnSe intermediate layer 3
06 and ZnMgSSe barrier layer 307, multiple quantum well structure 308, p-type ZnMgSSe cladding layer 30.
9, p-type ZnSe cap layer 310, p-type ZnSeTe
The contact layer 311 is sequentially stacked.

In this case, the upper portion of the p-type ZnMgSSe cladding layer 309, the p-type ZnSe cap layer 310 and the p-type ZnMgSSe cap layer 310 are formed.
The type ZnSeTe contact layer 311 is etched in a mesa stripe shape. Further, an insulating layer 312 is formed on the p-type ZnMgSSe cladding layer 309 other than the mesa stripe portion, and the p-type electrode 3 is formed on the p-type ZnSeTe contact layer 311 and the insulating layer 312.
13 is formed, and the n-type electrode 314 is formed on the back surface of the n-type GaAs substrate 301, as in the first embodiment.

The n-type GaAs substrate 301, the n-type GaAs buffer layer 302, the n-type ZnSe buffer layer 303, the n-type ZnMgSSe cladding layer 304, and the p-type ZnMgSSe.
Details of the configurations of the clad layer 309 and the p-type ZnSe cap layer 310 are the same as those in the first embodiment.

The multiple quantum well structure 308 has four layers of Zn0.7.
Cd0.3Se well layer (thickness 2.3 nm each) 305, three layers of ZnMg0.1S0.2Se0.8 barrier layer (thickness 4 nm each) 3
07 and all of the 8 well layers / barrier layers and the well layers / cladding layers at the interfaces of the ZnSe intermediate layers (thickness 0.5 each).
7 nm, that is, two molecular layers) 306. Well layer 30
The bandgap of 5 at room temperature is 2.46 eV. The lattice constant of Zn0.7Cd0.3Se is 0.5784 nm
Since there is a + 2.3% lattice mismatch with GaAs, compressive strain exists in the well layer 205. The composition of the barrier layer 307 is the n-type ZnMgSSe cladding layer 30.
4 and the p-type ZnMgSSe cladding layer 309 have the same composition. The composition of the barrier layer has a band gap of Z
When the active layer is ZnCdSe, Z is selected because the composition is selected from the band gap of the nMgSSe cladding layer or less.
It is selected from nSSe or ZnMgSSe.

In order to prevent the formation of impurity levels in the active layer, it is preferable to add neither n-type impurities nor p-type impurities to the well layer, the intermediate layer and the barrier layer.

The p-type ZnSeTe contact layer 311 is p
It is provided to obtain ohmic contact with the mold electrode 313. The structure of the contact layer 311 is, for example, ZnSe or Z.
Short-period structures of nTe and ZnSeTe are stacked, and the contact surface with the p-type electrode 313 is ZnTe. The contact layer 311 has a thickness of about 20 to 200 nm, for example, 5
0 nm. The carrier density of p-type ZnTe is 10 at maximum.
^It can be up to ¹⁹ cm ⁻³ , for example, 2 × 10 ¹⁸ cm ⁻³ . By providing such a structure, II-VI
The operating voltage of the group compound semiconductor laser can be significantly reduced to about 4 to 7V. However, ZnTe is Ga
Since there is a lattice mismatch of + 7.7% with respect to As and the critical film thickness is considered to be less than 5 nm, countless dislocations are present in the contact layer.

The operation and effect of the semiconductor laser configured as described above will be described. The critical film thickness of Zn0.7Cd0.3Se with respect to GaAs is considered to be about 15 nm, but in the present embodiment, the total film thickness of the Zn0.7Cd0.3Se well layer 305 is 9.2 nm, which is thinner than the critical film thickness. Therefore, it is considered that crystal defects are not generated due to lattice relaxation. However, since each well layer is as thin as 2.3 nm, that is, 8 molecular layers, the steepness of the change of the mixed crystal composition at the interface with the adjacent layer and the uniformity of the mixed crystal composition are dependent on the crystal quality of the well layer and the laser device. Has a great influence on the operating characteristics and reliability of the. This is because the imperfect crystal quality at the interface of the mixed crystal quantum well structure is considered to be the driving force for the growth of crystal defects. Therefore, at all well / barrier layers and well / clad layer interfaces, a bilayer compound Z
By providing the nSe intermediate layer 306, it is possible to suppress the mixed crystal fluctuation at the interface, enhance the steepness and composition uniformity of the composition at the interface, and improve the crystal quality of the well layer, thus improving the reliability of the device. be able to.

The thickness of the intermediate layer may be sufficient to enhance the steepness of compositional change and compositional uniformity at the interface, for example, 2 nm or less is sufficient. From the viewpoint of carrier transport efficiency, the compound used as the intermediate layer is preferably a compound having a band gap larger than that of the well layer and smaller than that of the barrier layer.

The method of manufacturing the semiconductor laser configured as described above is the same as that of the first embodiment. p-type ZnSe
As a raw material for MBE growth of the Te contact layer 311,
For example, a polycrystalline compound ZnTe is used.

Zn0.7Cd0.3Se well layer 305 and Z
The layer thickness of the nSe intermediate layer 306 can be easily controlled by controlling the opening / closing time of the cell shutter in units of 0.1 seconds. Further, in the case of controlling precisely on the order of molecular layers, so-called atomic layer epitaxy in which metal Zn, Cd and Se are used as raw materials to grow one atomic layer at a time can be performed.

Results obtained by continuously injecting a current at room temperature into the semiconductor laser device according to the present embodiment to evaluate the operating characteristics will be described. Oscillation wavelength is about 510 nm, threshold current is 51 mA, threshold current density is 1.5 kA / cm.
2. The external differential quantum efficiency is 59%, and the applied voltage at the start of laser oscillation is about 7V. Also, output 1 at 20 ° C
The device operating life at mW is about 45 minutes. From the above, according to the present embodiment, it is possible to improve the reliability of the II-VI group compound semiconductor laser device.

(Third Embodiment) FIG. 4 is a structural sectional view schematically showing a third embodiment of a semiconductor laser according to the present invention. This semiconductor laser has an optical guide layer and an active layer having lattice distortion.

As shown in FIG. 4, an n-type GaAs substrate 40
N-type GaAs buffer layer 402 and n-type ZnSe
Buffer layer 403, n-type ZnMgSSe cladding layer 40
4, n-type ZnSe / ZnSSe optical guide layer 405, Zn
CdSe active layer 406, p-type ZnSe / ZnSSe light guide layer 407, p-type ZnMgSSe cladding layer 408,
A p-type ZnSe cap layer 409 and a p-type ZnSeTe contact layer 410 are sequentially stacked. n-type GaAs substrate 401, n-type GaAs buffer layer 402, n-type ZnS
e buffer layer 403, p-type ZnSe cap layer 409,
p-type ZnSeTe contact layer 410, p-type electrode 412
The details of the contact structure and the structure of the n-type electrode 413 are the same as those in the second embodiment.

The compositions of the n-type ZnMgSSe cladding layer 404 and the p-type ZnMgSSe cladding layer 408 are Mg composition ratio 0.05 and S composition ratio 0.13, and ZnMgSSe having this composition lattice-matches with GaAs. Also,
The bandgap at room temperature is 2.80 eV. n-type Z
The thickness of the nMgSSe layer clad layer 404 is 1.0 μm,
The effective donor density is 5 × 10 ¹⁷ cm ⁻³ , and, for example, Cl is used as the n-type impurity. In addition, p-type ZnM
The gSSe cladding layer 408 has a thickness of 1.0 μm, an effective acceptor density of 3 × 10 ¹⁷ cm ⁻³ , and N is used as the p-type impurity.

The active layer 406 is Zn0.8C with a thickness of 11 nm.
The bandgap at room temperature is 2.43 eV. The lattice constant of Zn0.8Cd0.2Se is 0.5745 nm, which is + 1.6% that of GaAs.
The active layer 406 has compressive strain due to the lattice irregularity.

FIG. 5 is a diagram schematically showing the structure and lattice irregularity around the light guide layer. As shown in FIG. 5, n-type Z
nSe / ZnSSe optical guide layer 405 and p-type ZnS
The e / ZnSSe light guide layer 407 is the ZnSe layer 414.
And a layered structure of ZnS0.13Se0.87 layer 415,
ZnS0.13Se0.87 layer 4 with a thickness of 5 nm from the clad layer side
15 and a ZnSe layer 414 having a thickness of 5 nm are repeatedly laminated for 8 cycles, and a ZnS0.13Se0.87 layer 4 having a thickness of 20 nm is further formed.
15 is laminated up to the interface with the active layer 406. Zn
The lattice constant of Se is 0.56693 nm, which has a lattice mismatch of + 0.28% with respect to GaAs.
Se 0.87 has a lattice constant of 0.56355 nm and is made of GaAs.
There is a lattice mismatch of -0.31%. Therefore, in the laminated structure composed of the ZnSe layer and the ZnS0.13Se0.87 layer having the same thickness, the total strain is close to zero.

The composition of the light guide layer is selected so that the refractive index at the emission wavelength of the active layer is larger than that of the cladding layer and smaller than that of the active layer, and the band gap is equal to that of the cladding layer. It is chosen to be smaller than the bandgap and larger than the bandgap of the active layer. When the active layer is ZnCdSe, in order to apply tensile strain to at least a part of the optical guide layer, ZnSSe or ZnMgSSe having tensile strain may be used.

In order to prevent the formation of impurity levels in the active layer, the active layer 406 of the optical guide layers 405 and 407 is to be prevented.
It is preferable that neither n-type impurities nor p-type impurities are added to the region near the interface with. In the extreme, n is applied to the entire light guide layer.
It is not necessary to add any type or p-type impurities. The effective donor density and the effective acceptor density of the doped region are, for example, 5 × 10 ¹⁷ cm ⁻³ and 4 ×, respectively.
10 ¹⁷ cm ^-3 .

The operation and effect of the semiconductor laser configured as described above will be described. The critical thickness of Zn0.8Cd0.2Se for GaAs is about 15 to 20 nm, and since the thickness of the active layer 406 is smaller than the critical thickness, it is considered that crystal defects due to lattice relaxation do not occur.

In the present embodiment, the light guide layer 40
5 and 407, the ZnS0.13Se0.87 layer 415 having a thickness of 20 nm is provided at the interface in contact with the active layer 406, so that the tensile strain applied to the optical guide layers 405 and 407 compensates the compressive strain applied to the active layer 406. As a result, the sum is close to a non-distorted state. Therefore, the generation and multiplication of defects in the active layer 406 are suppressed, and the reliability of the device can be improved.

Regarding the degree of strain compensation, it is not always necessary to have a total strain-free state as in this embodiment, and a total compression strain or tensile strain may exist. However, also in this case, the thickness of each layer constituting the light guide layer is designed to be thinner than the critical film thickness. Further, in the present embodiment, the strain is compensated symmetrically with respect to the active layer, but the strain may be asymmetric, or the optical guide layer on only one side of the active layer may compensate the strain. Alternatively, the strain may be compensated in a region not adjacent to the active layer.

The method of manufacturing the semiconductor laser configured as described above is the same as in the first and second embodiments. The semiconductor laminated structure and its composition in the present embodiment are ZnM
S composition ratio of gSSe clad layer and ZnS in optical guide layer
Since the S composition ratio of the Se layer is the same, it is not necessary to change the molecular beam intensity of ZnS during the growth, which is an advantage in MBE crystal growth. II-VI continuously without interruption
A group compound semiconductor layer can be formed.

The results of evaluating the operating characteristics of the semiconductor laser device according to the present embodiment by continuously injecting a current at room temperature will be described. Oscillation wavelength is about 517 nm, threshold current is 75 mA, threshold current density is 2.1 kA / cm.
2. The external differential quantum efficiency is 56%, and the applied voltage at the start of laser oscillation is about 6V. Also, output 1 at 20 ° C
The device operating life at mW is about 40 minutes. From the above, according to the present embodiment, it is possible to improve the reliability of the II-VI group compound semiconductor laser device.

(Fourth Embodiment) FIG. 6 is a structural sectional view schematically showing a fourth embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a single quantum well structure and a light guide layer.

As shown in FIG. 6, an n-type GaAs substrate 60
N-type GaAs buffer layer 602 and n-type ZnSe
Buffer layer 603, n-type ZnMgSSe cladding layer 60
4, n-type ZnSSe light guide layer 605, ZnCdSe quantum well active layer 606, ZnSe intermediate layers 607 adjacent to both sides thereof, p-type ZnSSe light guide layer 608, p-type Zn
The MgSSe clad layer 609, the p-type ZnSe cap layer 610, and the p-type ZnSeTe contact layer 611 are sequentially stacked. n-type GaAs substrate 601, n-type Ga
As buffer layer 602, n-type ZnSe buffer layer 60
3, n-type ZnMgSSe cladding layer 604, ZnSe intermediate layer 607, p-type ZnMgSSe cladding layer 609, p
The details of the contact structure for the p-type ZnSe cap layer 610, the p-type ZnSeTe contact layer 611, the p-type electrode 613, and the structure of the n-type electrode 614 are the same as those in the second embodiment.

N-type ZnSSe optical guide layer 605 and p
The composition of the ZnSSe optical guide layer 608 has an S composition ratio of 0.0.
6, ZnSSe having this composition lattice-matches with GaAs. The bandgap at room temperature is 2.75.
eV. The thickness of each of the light guide layers 605 and 608 is 100 nm. In order to prevent the formation of impurity levels in the active layer, it is preferable to add neither n-type impurities nor p-type impurities to the region near the interface with the intermediate layer 607 in the optical guide layer. In the extreme, it is possible to add neither n-type impurities nor p-type impurities to the entire light guide layer. The effective donor density and the effective acceptor density of the doped region are, for example, 5 × 10 ¹⁷ cm ⁻³ and 4 × 10 ¹⁷ cm ⁻³ , respectively.

The quantum well active layer 606 is made of Zn having a thickness of 6 nm.
It is composed of 0.8 Cd 0.2 Se and has a band gap of 2.45 eV at room temperature. The lattice constant of Zn0.8Cd0.2Se is 0.5745 nm, which is +1.6 relative to GaAs.
%, There is a compressive strain in the active layer 606. However, since it is thinner than the critical film thickness, it is considered that crystal defects due to lattice relaxation do not occur.

The ZnSe intermediate layers 607 adjacent to both sides of the active layer 606 each have a thickness of 1.1 nm, that is, four molecular layers. By providing the intermediate layer, the steepness of the mixed crystal composition change and the uniformity of the mixed crystal composition at the active layer / light guide layer interface can be increased, and the crystal quality of the active layer can be improved, so that the reliability of the device can be improved. it can. The thickness of the intermediate layer is sufficient if it is sufficient to enhance the steepness of composition change and composition uniformity at the interface, and for example, 2 nm or less is sufficient.

In order to prevent the formation of impurity levels in the active layer, it is preferable to add neither n-type impurities nor p-type impurities to active layer 606 and intermediate layer 607.

The method of manufacturing the semiconductor laser configured as described above is the same as that of the second embodiment.

The results of evaluating the operating characteristics of the semiconductor laser device according to the present embodiment by continuously injecting a current at room temperature will be described. Oscillation wavelength is about 512 nm, threshold current is 66 mA, threshold current density is 1.9 kA / cm.
2. The external differential quantum efficiency is 64%, and the applied voltage at the start of laser oscillation is about 7V. Also, output 1 at 20 ° C
The device operating life at mW is about 45 minutes. From the above, according to the present embodiment, it is possible to improve the reliability of the II-VI group compound semiconductor laser device.

(Fifth Embodiment) FIG. 7 is a structural sectional view schematically showing a fifth embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a strained layer in the lower cladding layer.

As shown in FIG. 7, an n-type GaAs substrate 70
N-type GaAs buffer layer 702 and n-type ZnSe
Buffer layer 703, n-type ZnMgSSe cladding layer 70
4, ZnSSe strained layer 705, n-type ZnMgSSe cladding layer 704, n-type ZnSSe optical guide layer 706, ZnC
A dSe quantum well active layer 707, a p-type ZnSSe optical guide layer 708, a p-type ZnMgSSe cladding layer 709, a p-type ZnSe cap layer 710, and a p-type ZnSeTe contact layer 711 are sequentially stacked. The details of the configuration other than the ZnSSe strained layer 705 are the same as in the fourth embodiment.

The ZnSSe strained layer 705 curves dislocations originating from stacking faults generated at the interface between the GaAs buffer layer 702 and the ZnSe buffer layer 703 to form a closed loop. The dislocation density can be reduced. It is also possible to prevent dislocations from rising to the active layer region during the operation of the laser device. Therefore, the reliability of the device can be improved. Zn
The SSe strained layer 705 is n-type Zn0.9M with a thickness of 1.2 μm.
g0.1S0.2Se0.8 provided in the central portion of the cladding layer 704 and having a thickness of 2.8 nm, that is, 10 molecular layers of ZnS0.2S.
e0.8. With this composition,
There is a lattice mismatch of 0.6%, and the critical film thickness is considered to be about 60 nm. Also, the same S as the ZnMgSSe clad layer is used.
Since it has a composition ratio, it can be easily formed in MBE crystal growth by closing the shutter of the cell for the Mg source for a predetermined time during the growth of the n-type ZnMgSSe cladding layer.

In this embodiment, a reduction in dislocation density was observed in the layers above the strained layer 705 by TEM observation, but the composition and structure of the strained layer 705 are not necessarily optimized. Conversely, the composition and structure can be selected in order to optimize the strain energy applied to the system. When a ZnMgSSe layer is used for the cladding layer, ZnS, ZnSe, ZnM other than ZnSSe as the strain layer
gS or ZnMgSe is preferably selected.

According to the present embodiment, the reliability of the II-VI group compound semiconductor laser device can be improved as in the case of the above-mentioned embodiments.

(Sixth Embodiment) FIG. 8 is a structural sectional view schematically showing a sixth embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a strained superlattice layer in the lower cladding layer.

As shown in FIG. 8, an n-type GaAs substrate 80
N-type GaAs buffer layer 802 and n-type ZnSe
Buffer layer 803, n-type ZnMgSSe cladding layer 80
4, ZnSSe / ZnSeTe strained superlattice layer 805, n-type ZnMgSSe cladding layer 804, n-type ZnSSe optical guide layer 806, ZnCdSe quantum well active layer 807, p
The type ZnSSe light guide layer 808, the p-type ZnMgSSe cladding layer 809, the p-type ZnSe cap layer 810, and the p-type ZnSeTe contact layer 811 are sequentially stacked. The details of the configuration other than the ZnSSe / ZnSeTe strained superlattice layer 805 are the same as in the fifth embodiment.

ZnSSe / ZnSeTe strained superlattice layer 80
In No. 5, since dislocations originating from stacking faults generated at the interface between the GaAs buffer layer 802 and the ZnSe buffer layer 803 are curved to form a closed loop, the dislocation density in the layer thereabove, particularly the active layer, can be reduced. It is also possible to prevent dislocations from rising to the active layer region during the operation of the laser device. Therefore, the reliability of the device can be improved. The ZnSSe / ZnSeTe strained superlattice layer 805 is a 1.2 μm thick n-type Zn0.9Mg0.1S0.2 layer.
It is provided in the center of the Se0.8 cladding layer 704 and has a thickness of 2.2 nm, that is, 8 molecular layers of ZnS0.2Se0.8, and a thickness of 1.2 nm, that is, 2 molecular layers of ZnSe0.7Te0.3, which are repeated for 4 cycles. It has a laminated structure. ZnS0.2
Se 0.8 has a lattice mismatch of −0.6% with respect to GaAs, and the critical film thickness is considered to be about 60 nm.
0.7Te0.3 has a lattice mismatch of + 2.6% with respect to GaAs, and the critical film thickness is considered to be about 10 nm.

Since the ZnS0.2Se0.8 layer has the same S composition ratio as that of the ZnMgSSe clad layer, ZnSe0.7
Since the Te0.3 layer has the same composition as the mixed crystal layer used for the p-type ZnSeTe contact layer 811, in MBE crystal growth, it can be easily formed continuously without interruption during the growth of the n-type ZnMgSSe cladding layer. can do.

In this embodiment, a reduction in dislocation density was observed in the layers above the ZnSSe / ZnSeTe strained superlattice layer 805 by TEM observation, but the composition and structure of the strained superlattice layer 805 were not necessarily optimized. It has not been done. Conversely, the composition and structure can be selected in order to optimize the strain energy applied to the system. In the present embodiment, the ZnSSe / ZnSeTe strained superlattice layer 8 is used.
05 is an n-type Zn0.9Mg0.1S0.2Se0.8 cladding layer 70
Although only one set is provided in the central portion of No. 4, two or more sets may be provided. For example, disposing the n-type Zn0.9Mg0.1S0.2Se0.8 clad layer 704 at three equally divided positions, one set at a total of two sets, is expected to further reduce the dislocation density. The composition of the strained superlattice layer is ZnMgSS.
When using the e-cladding layer, Zn, Mg, Cd, S, S
Two or more kinds of compounds or mixed crystals composed of an element selected from e and Te are preferable.

According to this embodiment, the reliability of the II-VI group compound semiconductor laser device can be improved as in the case of the above-mentioned embodiments.

(Embodiment 7) FIG. 9 is a structural sectional view schematically showing a seventh embodiment of a semiconductor laser according to the present invention. This semiconductor laser has a ZnSe buffer layer substantially free of n-type and p-type impurities.

As shown in FIG. 9, an n-type GaAs substrate 90
1, n-type GaAs buffer layer 902, ZnSe buffer layer 903, n-type ZnSe buffer layer 904, and n-type Z
nMgSSe cladding layer 905, n-type ZnSSe optical guide layer 906, ZnCdSe quantum well active layer 907, p-type ZnSSe optical guide layer 908, p-type ZnMgSSe cladding layer 909, p-type ZnSe cap layer 910 and p.
A type ZnSeTe contact layer 911 is sequentially stacked. The details of the configuration other than the ZnSe buffer layer 903 and the n-type ZnSe buffer layer 904 are the same as those in the fourth embodiment.

The ZnSe buffer layer 903 is n-type and p-type.
The layer is substantially free of any type impurities, and its thickness is selected to be 10 molecular layers or less, that is, 2.8 nm or less, for example, 6 molecular layers, that is, 1.7 nm. In addition, n-type Zn
The Se buffer layer 904 has a thickness of 30 nm and an effective donor density of 2 × 10 18 cm −3.

As described above, the n-type GaAs buffer layer 9
By providing a ZnSe layer to which no n-type impurity is added at the interface with 02, two-dimensional growth occurs immediately after the growth of ZnSe, and three-dimensional growth that occurs due to the presence of n-type impurities such as Cl is suppressed. Type GaAs buffer layer 902
It is possible to reduce the density of stacking faults generated from the interface with the. Therefore, the density of crystal defects such as stacking faults and dislocations in the active layer can be reduced, and the generation and multiplication of dislocations in the active layer during operation of the laser element can be suppressed.

Also, n-type ZnSe having a high effective donor density
When the buffer layer 904 is provided on the ZnSe buffer layer 903, the thickness of the depletion layer formed on the II-VI group compound semiconductor side of the junction surface between GaAs and the II-VI group compound semiconductor can be reduced, and at this interface. Since the voltage drop can be suppressed, the voltage applied to the laser element can be reduced. But,
When the effective donor density exceeds 3 × 10 19 cm −3, the strain of the crystal lattice becomes large, and conversely the crystal quality is deteriorated.

The effective donor density of the n-type ZnMgSSe cladding layer 905 is 5 × 10 ¹⁷ cm ⁻³ , but the n-type ZnS
The effective donor density does not need to change discontinuously or abruptly at the interface with the e buffer layer 904, and may change continuously or gently in the interface vicinity region from the buffer layer 904 near the interface to the cladding layer 905. The effective donor density can be controlled by controlling the cell temperature of the n-type impurity source, for example.

According to the present embodiment, the reliability of the II-VI group compound semiconductor laser device can be improved as in the case of the above-mentioned embodiments.

(Embodiment 8) FIG. 10 is a structural sectional view schematically showing an eighth embodiment of a semiconductor laser according to the present invention.

As shown in FIG. 10, n-type GaAs substrate 1
N type GaAs buffer layer 1002 and n type Z on 001
nSe buffer layer 1003, n-type ZnMgSSe cladding layer 1004, n-type ZnSSe light guide layer 1005, Z
nCdSe quantum well active layer 1006, p-type ZnSSe optical guide layer 1007, p-type ZnMgSSe cladding layer 10
08, p-type ZnSe cap layer 1009 and p-type Zn
A SeTe contact layer 1010 is sequentially stacked.
The details of the configuration other than the n-type ZnSe buffer layer 1003 are the same as in the fourth embodiment. In this embodiment, the semiconductor laser shown in FIG. 10 is replaced with the n-type ZnSe buffer layer 100.
3 is manufactured by making the growth temperature of No. 3 higher than the growth temperature of the semiconductor layer laminated thereon. For example, crystal growth of a semiconductor laminated structure is performed by the MBE method.

In general, when the growth temperature is lowered, the growth rate is increased, the re-evaporation of attached atoms is suppressed, the surface flatness is improved, and the incorporation of impurities is promoted, so that the carrier density is increased. However, since surface diffusion of attached atoms is suppressed, when three-dimensional growth occurs, the three-dimensional growth proceeds as it is and stacking faults are easily formed. On the contrary, when the growth temperature is increased, re-evaporation is promoted and the surface flatness is deteriorated, but surface diffusion is also promoted, so that the two-dimensional growth is easily maintained. There is an optimum growth temperature region between them. The growth temperature of the ZnMgSSe-based semiconductor by the MBE method is preferably 260 to 330 ° C.

In the present embodiment, for example, n-type Z
The growth start temperature of the nSe buffer layer 1002 is set to 310 ° C., and then the growth temperature is continuously lowered during the growth to 290 ° C. during the growth of the buffer layer. And n-type ZnM
The growth temperature after the gSSe cladding layer 1004 is also 290 ° C.
As a result, the semiconductor laminated structure is continuously grown without interrupting the growth. More specifically, n with a thickness of 30 nm
The type ZnSe buffer layer 1002 was grown for 4 minutes, but at the same time as the growth was started, the growth temperature was lowered from 310 ° C. to 290 ° C. at a temperature decrease rate of 10 ° C./min.

As a result, the n-type ZnSe buffer layer 10 is formed.
In the initial stage of growth of 02, Zn and Se surface diffusion is promoted,
From the interface with the n-type GaAs buffer layer 1002, ZnSe
The two-dimensional growth is started, and the three-dimensional growth that becomes the nucleus of the point defect is suppressed, so that the density of stacking faults generated from the interface with the n-type GaAs buffer layer 1002 can be reduced. The surface of the laser structure formed thereon has good flatness. Therefore, the density of crystal defects such as stacking faults and dislocations in the active layer can be reduced, and the generation and multiplication of dislocations in the active layer during operation of the laser element can be suppressed. In addition, n-type and p-type impurities can be added efficiently.

In the present embodiment, the growth temperature is lowered during the growth of the buffer layer to continuously grow the growth without interruption, but the growth is performed after the growth of the buffer layer or during the growth. The growth temperature may be lowered by interruption.

According to the present embodiment, the reliability of the II-VI group compound semiconductor laser device can be improved as in the case of the above-mentioned embodiments.

(Ninth Embodiment) A ninth embodiment of the semiconductor laser according to the present invention is the same as the semiconductor laser shown in FIG. 10, except that the n-type ZnSSe optical guide layer 1005 and ZnCd are used.
The Se quantum well active layer 1006 and the p-type ZnSSe optical guide layer 1007 are manufactured at a higher growth temperature than the growth temperature of the other II-VI group compound semiconductor layers. For example, crystal growth of a semiconductor laminated structure is performed by the MBE method.

Generally, when the growth temperature is increased, the incorporation of impurities is suppressed and the carrier density is reduced. In order to improve the crystal quality of the active layer, it is desirable that the n-type and p-type impurities are not substantially contained. Therefore, it is advisable to grow the active layer at a temperature as high as possible such that the crystal quality does not deteriorate due to the re-evaporation of the attached atoms.

In the present embodiment, for example, n-type Z
nSSe optical guide layer 1005, ZnCdSe quantum well active layer 1006 and p-type ZnSSe optical guide layer 1007.
Growth temperature is set to 320 ° C., the growth temperature of the other II-VI group compound semiconductor layers is set to 290 ° C., and growth is suspended while the growth temperature is changed.

As a result, formation of impurity levels in the active layer can be suppressed, and dislocations and multiplication in the active layer can be suppressed during operation of the laser device.

The time required to grow an active layer is usually 3
The time required to grow the light guide layers above and below the active layer is around 20 minutes, while it is around 0 seconds. From the viewpoint of following the actual temperature with respect to the change of the set temperature and reproducibility of the growth temperature of the active layer, it is preferable to raise the temperature to the growth temperature of the active layer when growing the optical guide layer.

The present embodiment also has an advantage from the viewpoint of simplicity and reproducibility of the crystal growth method and apparatus.
That is, as a result of examining the temperature dependence of the sticking coefficient of S, 2
ZnS molecular beam intensity required to grow Zn0.9Mg0.1S0.2Se0.8 cladding layer at 90 ℃ and Zn at 320 ℃
S0.06Se0.94 Zn required for growing the light guide layer
Since the molecular beam intensity of S is the same, it is not necessary to change the molecular beam intensity of ZnS during the growth. Therefore, one ZnS raw material cell is sufficient.

In the present embodiment, the growth temperature was changed by interrupting the growth before and after the growth of the active layer and the light guide layer. However, the growth temperature is changed during the growth of the light guide layer. It may grow continuously without interruption.

According to the present embodiment, the reliability of the II-VI group compound semiconductor laser device can be improved as in the case of the above-mentioned embodiments.

[0124]

As described above, according to the present invention, the generation and multiplication of crystal defects occurring in the active layer during operation are suppressed,
Further, it is possible to obtain the remarkable effects of improving the crystal quality of the active layer and improving the reliability of the II-VI group compound semiconductor light emitting device.

[Brief description of drawings]

FIG. 1 is a structural sectional view of a semiconductor laser according to a first embodiment of the present invention.

FIG. 2 is a diagram showing lattice misalignment around a strained multiple quantum well structure of a semiconductor laser according to the first embodiment of the present invention.

FIG. 3 is a structural sectional view of a semiconductor laser according to a second embodiment of the present invention.

FIG. 4 is a structural sectional view of a semiconductor laser according to a third embodiment of the present invention.

FIG. 5 is a diagram showing a structure and lattice irregularity around a light guide layer of a semiconductor laser according to a third embodiment of the present invention.

FIG. 6 is a structural sectional view of a semiconductor laser according to a fourth embodiment of the present invention.

FIG. 7 is a structural sectional view of a semiconductor laser according to a fifth embodiment of the present invention.

FIG. 8 is a structural sectional view of a semiconductor laser according to a sixth embodiment of the present invention.

FIG. 9 is a structural cross-sectional view of a semiconductor laser according to a seventh embodiment of the present invention.

FIG. 10 is a structural sectional view of a semiconductor laser according to an eighth embodiment of the present invention.

[Explanation of symbols]

101, 301, 401, 601, 701, 801, 9
01,1001 n-type GaAs substrate 102,302,402,602,702,802,9
02,1002 n-type GaAs buffer layer 103,303,403,603,703,803,9
04,1003 n-type ZnSe buffer layer 104,304,404,604,704,804,9
05,1004 n-type ZnMgSSe cladding layer 105 Zn0.8Cd0.2Se well layer 106 ZnS0.2Se0.8 barrier layer 107 strained multiple quantum well structure 108,309,408,609,709,809,9
09,1008 p-type ZnMgSSe cladding layer 109 p-type ZnSe contact layer 110,312,411,612,712,812,9
12, 1011 Insulating layer 111, 313, 412, 613, 713, 813, 9
13,1012 p-type electrode 112,314,413,614,714,814,9
14,1013 n-type electrode 305 ZnCdSe well layer 306,607 ZnSe intermediate layer 307 ZnMgSSe barrier layer 308 Multiple quantum well structure 310,409,610,710,810,910,1
P-type ZnSe cap layer 311, 410, 611, 711, 811, 911, 1
010 p-type ZnSeTe contact layer 405 n-type ZnSe / ZnSSe light guide layer 406 ZnCdSe active layer 407 p-type ZnSe / ZnSSe light guide layer 414 ZnSe layer 415 ZnS0.13Se0.87 layer 605,706,806,906,1005 n-type Zn
SSe optical guide layer 606, 707, 807, 907, 1006 ZnCd
Se quantum well active layer 608, 708, 808, 908, 1007 p-type Zn
SSe optical guide layer 705 ZnSSe strained layer 805 ZnSSe / ZnSeTe strained superlattice layer 903 ZnSe buffer layer

Claims (27)

[Claims] 1. A semiconductor light emitting device having a II-VI group compound semiconductor having a strained multiple quantum well structure, the semiconductor light emitting device having a barrier layer having a lattice strain opposite to the lattice strain of the well layer. 2. A strained multi-quantum well structure, comprising GaA
II-VI lattice-matched to s substrate or ZnSe substrate
The semiconductor light emitting device having a group compound semiconductor, wherein the well layer is made of ZnCdSe and the barrier layer has a composition having tensile strain. 3. A semiconductor light emitting device having a II-VI group compound semiconductor having a multiple quantum well structure, wherein the well layer and the barrier layer are a mixed crystal composed of at least three kinds of elements. A semiconductor light emitting device comprising a layer and an intermediate layer made of a compound between the barrier layer. 4. GaAs having a multiple quantum well structure,
The semiconductor light emitting device having a II-VI group compound semiconductor lattice-matched to a substrate or a ZnSe substrate, wherein the well layer is made of ZnCdSe, the barrier layer is made of ZnSSe or ZnMgSSe, and the intermediate layer is made of ZnSe. Semiconductor light emitting device. 5. A semiconductor light emitting device having a II-VI group compound semiconductor having a strained multiple quantum well structure, comprising a barrier layer having a lattice strain opposite to that of the well layer.
4. The semiconductor light-emitting device according to claim 1, wherein the well layer and the barrier layer are made of a mixed crystal composed of at least three kinds of elements, and an intermediate layer made of a compound is provided between the well layer and the barrier layer. element. 6. A GaA having a strained multiple quantum well structure.
II-VI lattice-matched to s substrate or ZnSe substrate
In a semiconductor light emitting device having a group compound semiconductor, the well layer is made of ZnCdSe, the barrier layer is made of ZnSSe or ZnMgSSe having tensile strain, and the intermediate layer provided between the well layer and the barrier layer is made of ZnSe. 6. The semiconductor light emitting device according to claim 5. 7. A semiconductor light emitting device having a II-VI group compound semiconductor, comprising a light guide layer and an active layer having a lattice strain, wherein at least a part of the light guide layer is opposite to the lattice strain of the active layer. A semiconductor light emitting device composed of a composition having a lattice strain of. 8. A semiconductor light emitting device comprising an II-VI group compound semiconductor lattice-matched to a GaAs substrate or a ZnSe substrate, comprising a light guide layer and an active layer having a lattice strain, wherein the active layer is made of ZnCdSe. 8. The semiconductor light emitting device according to claim 7, wherein at least a part of the light guide layer has a composition having tensile strain. 9. An I having a quantum well structure and an optical guide layer.
A semiconductor light emitting device having a group I-VI compound semiconductor, wherein the well layer and the light guide layer are a mixed crystal composed of at least three kinds of elements, and a compound is formed between the well layer and the light guide layer. A semiconductor light emitting device having an intermediate layer. 10. A semiconductor light emitting device comprising a II-VI group compound semiconductor lattice-matched to a GaAs substrate or a ZnSe substrate, comprising a quantum well structure and a light guide layer, wherein the well layer is made of ZnCdSe, The semiconductor light emitting device according to claim 9, wherein the layer is made of ZnSSe or ZnMgSSe, and the intermediate layer is made of ZnSe. 11. A semiconductor light emitting device having a II-VI group compound semiconductor having a strained quantum well structure and an optical guide layer, wherein the well layer and the optical guide layer are mixed crystals composed of at least three or more kinds of elements. Comprising an intermediate layer made of a compound between the well layer and the light guide layer,
10. The semiconductor light emitting device according to claim 7, wherein at least a part of the light guide layer has a composition having a lattice strain opposite to that of the well layer. 12. A semiconductor light emitting device having a strained quantum well structure and an optical guide layer, comprising a II-VI group compound semiconductor lattice-matched to a GaAs substrate or a ZnSe substrate, wherein the well layer is made of ZnCdSe, The semiconductor light emitting device according to claim 11, wherein at least a part of the guide layer is made of ZnSSe or ZnMgSSe having tensile strain, and the intermediate layer is made of ZnSe. 13. A semiconductor light emitting device comprising a II-VI group compound semiconductor, wherein at least one semiconductor layer having a lattice constant different from that of the substrate is provided in a clad layer closer to the substrate than the active layer. And a semiconductor light emitting device characterized in that the thickness of the semiconductor layer is smaller than a critical film thickness for the substrate. 14. The cladding layer is made of ZnMgSSe, and the semiconductor layer is made of ZnS, ZnSe, ZnSSe, Z.
The semiconductor light emitting device according to claim 13, comprising nMgS or ZnMgSe. 15. A semiconductor light emitting device comprising a II-VI group compound semiconductor, wherein a strained superlattice layer is provided in a clad layer closer to the substrate than the active layer. . 16. The clad layer is made of ZnMgSSe, and the strained superlattice layer is made of two or more kinds of compounds or mixed crystals composed of elements selected from Zn, Mg, Cd, S, Se and Te. The semiconductor light emitting device according to claim 15. 17. A semiconductor light emitting device made of a II-VI group compound semiconductor formed on a III-V group compound semiconductor substrate, wherein n-type and p-type impurities are substantially formed on the substrate surface. A semiconductor light emitting device comprising a II-VI group compound semiconductor layer not containing the semiconductor layer, and the semiconductor layer having a thickness of 10 molecular layers or less. 18. A II-VI group compound semiconductor layer containing the impurity in an amount of 1 × 10 ¹⁸ cm ⁻³ or more on the II-VI group compound semiconductor layer containing substantially no n-type or p-type impurities. 2. The laminated structure according to claim 1, wherein
7. The semiconductor light emitting device according to 7. 19. The III-V compound semiconductor substrate is G
The II-VI group compound semiconductor layer which is an aAs substrate and is substantially free of the n-type and p-type impurities is Zn.
19. The semiconductor light emitting device according to claim 17, which is Se. 20. A method for manufacturing a semiconductor light emitting device made of a II-VI group compound semiconductor formed on a III-V group compound semiconductor substrate, comprising II-V laminated on the substrate.
A method for manufacturing a semiconductor light emitting device, wherein the temperature for growing at least a part of the group I compound semiconductor buffer layer is higher than the growth temperature of the semiconductor layer laminated thereon. 21. The III-V compound semiconductor substrate is G
21. The semiconductor light emitting device according to claim 20, wherein the semiconductor light emitting device is an aAs substrate, and the II-VI group compound semiconductor buffer layer is ZnSe. 22. The method of manufacturing a semiconductor light emitting device according to claim 20, wherein the growth of the semiconductor layer is stopped after the growth of the buffer layer or during the growth to lower the growth temperature. 23. The method of manufacturing a semiconductor light emitting device according to claim 20, wherein the growth temperature of the buffer layer is lowered during the growth of the buffer layer so that the growth of the semiconductor layer is not interrupted. 24. A method for manufacturing a semiconductor light emitting device comprising a II-VI group compound semiconductor, wherein a temperature at which a semiconductor layer including at least an active layer is grown is higher than a growth temperature of a semiconductor layer other than the semiconductor layer. And a method for manufacturing a semiconductor light emitting device. 25. The growth temperature of the active layer and the light guide layer is higher than the growth temperature of the semiconductor layers other than the active layer and the light guide layer.
The manufacturing method of the semiconductor light emitting device according to the above. 26. The method for manufacturing a semiconductor light emitting device according to claim 25, wherein the growth of the semiconductor layer is interrupted before and after the growth of the active layer and the light guide layer to change the growth temperature. 27. The method of manufacturing a semiconductor light emitting device according to claim 25, wherein the growth temperature is changed during the growth of the light guide layer so that the growth of the semiconductor layer is not interrupted.