JPH07211988A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To obtain an InGaAs type semiconductor light emitting element having a high characteristic temperature and high light emitting efficiency by forming its active layer of InGaAs or InGaAsP and clad layers of ZnSSe of ZnCdSSe. CONSTITUTION:A semiconductor light emitting element is provided with clad layers 3 and 5 on both sides of an active layer 4. The active layer 4 is formed of InGaAs or InGaAsP and the clad layers 3 and 5 are formed of ZnSSe or ZnCdSSe. Or, after successively depositing the clad layers 3 and 5 composed of ZnSSe on a substrate 1 composed of GaAs, the active layer 4 having a different lattice constant front that of the layers 3 and 5 and composed of Inlays is deposited on the layers 3 and 5. Therefore, the difference in refractive index between the active layer 4 and clad layers 3 and 5 can be increased and large conductive zone offset energy can be realized while an appropriate lattice constant difference is maintained between the active layer 4 and clad layers 3 and 5.

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 having a high characteristic temperature, which comprises a II-VI group compound semiconductor as a cladding layer and an InGaAs III-V group compound semiconductor as an active layer.

A light emitting element used in a subscriber system device for bidirectional communication of a wavelength of 1.3 μm, for example, a semiconductor laser includes a semiconductor light emitting element using an InGaAs type III-V group compound semiconductor as an active layer. Attention has been paid.

A semiconductor light-emitting element used in a wide temperature range and required to have strict characteristics, such as a semiconductor laser used in such a two-way communication subscriber system device, has a threshold depending on the ambient temperature. It is required that the fluctuations of the value current and the light output are small.

Therefore, there is a need for an InGaAs semiconductor light emitting device having a high characteristic temperature.

[0005]

2. Description of the Related Art As a semiconductor laser having a high characteristic temperature used in a wavelength band of 1.3 μm, a strain I using a GaAs substrate is used.
The nGaAs semiconductor laser is promising and is being developed. This strained InGaAs semiconductor laser has a GaAs layer or an InGaP layer deposited on a GaAs substrate as a cladding layer and is epitaxially grown on the cladding layer.
The InGaAs thin layer having a lattice constant different from that of the clad layer is used as the active layer, and the InGaAs thin layer which is the active layer has a large strain.

However, the cladding layer is GaAs or InG.
In the conventional strained InGaAs semiconductor laser made of aP,
Since the difference in the lowest energy level of the conduction band between the active layer and the cladding layer (hereinafter referred to as "conduction band offset energy") is small, the overflow of electrons from the active layer to the cladding layer is large, and the characteristics of the semiconductor light emitting device It was difficult to raise the temperature sufficiently.

In order to suppress electron overflow and increase the characteristic temperature, it is effective to use a compound semiconductor having a large forbidden band width as a cladding layer and increase the conduction band offset energy. However, II with a large forbidden band
When a group IV compound semiconductor is used as a cladding layer, the difference in lattice constant from InGaAs, which is an active layer, becomes too large, and it is difficult to form an active layer with few crystal defects.

Further, InG which is a III-V group compound semiconductor
Since the clad layer made of the same III-V group compound semiconductor is used for the active layer of aAs-based crystal, the difference in the refractive index between the active layer and the clad layer is small. Can't be trapped. For this reason,
There is a problem of low luminous efficiency.

[0009]

As described above, in the conventional semiconductor light emitting device using the InGaAs type crystal as the active layer, the same III-V group compound semiconductor as that of the active layer is used also for the cladding layer. Therefore, there is a problem that the difference in refractive index between the clad layer and the active layer is small, and the luminous efficiency of the light emitting element is small. In addition, the difference in lattice constant between the clad layer and the active layer must be limited within a certain value, and a semiconductor with a large forbidden band cannot be used for the clad layer.
There is a drawback that the characteristic temperature of the light emitting device is low.

The present invention provides a II-VI group compound semi-conductor for the cladding layer.
Zn which is a conductor_1-xCd_xS_ySe _1-y(When x = 0
Is included in the active layer and the cladding layer.
The difference in refractive index is increased, and the difference between the cladding layer and the active layer
Large conduction band offset while maintaining an appropriate lattice constant difference.
Realization of high energy, high characteristic temperature and high light emission
Provide InGaAs semiconductor light emitting device having high efficiency
The purpose is to

[0011]

FIG. 2 is a sectional view of an embodiment of the present invention and shows a sectional structure of a stripe type semiconductor laser.

In order to solve the above problems, referring to FIG. 2, the first structure of the present invention has an active layer 4 and clad layers 3 and 5 sandwiching the active layer 4. In the semiconductor light emitting device, the active layer 4 is InGaAs or In
It is made of GaAsP, and the cladding layers 3 and 5 are made of ZnSS.
e or ZnCdSSe, and the second structure is the semiconductor light emitting device of the first structure in which GaAs is used as the substrate 1 and the cladding layers 3, 5
Is composed of ZnSSe deposited on the substrate 1, and the active layer 4 is composed of InGaAs having a lattice constant different from those of the cladding layers 3 and 5 deposited on the cladding layer 3. .

[0013]

In the semiconductor light emitting device according to the present invention, InGaAsP or InGaAs which is a III-V group compound semiconductor is used as an active layer, and ZnCdSSe or ZnSSe which is a II-VI group compound semiconductor is used as a cladding layer. These II-VI group compound semiconductors have a lower refractive index than III-V group compound semiconductors such as GaAs or InGaP.
The light confining effect of the semiconductor light emitting device having the II-VI group compound semiconductor as the clad layer is greater than that of the conventional light emitting device having the clad layer of GaAs or InGaP, and thus a device having high luminous efficiency is realized.

On the other hand, the energy band structure of the heterojunction between the II-VI group compound semiconductor and the III-V group compound semiconductor, especially the energy band structure of the heterojunction between ZnCdSSe or ZnSSe and InGaAsP or InGaAs, has not been clarified yet. First, it was unclear whether such a heterojunction had the carrier confinement effect required for light emitting devices. Therefore, no attempt to apply the above compound semiconductor to a semiconductor light emitting device having a double hetero structure has been reported yet, and it is unclear what characteristics such a device has.

The inventors of the present invention have found that ZnSSe and InGa
Calculate the energy band at the heterojunction with As,
The energy band structure was clarified. as a result,
In this heterojunction, it was clarified that sufficient conduction band offset energy was generated for carrier confinement. The contents of the calculation will be described below.

FIG. 1 is a diagram for explaining the principle of the present invention.
(A) is ZnS _y Se _1-y (y =
0.06) clad layer, In _{1-x '} Ga _x' As
(X ^' = 0.5) active layer, ZnS _y Se
The outline of the calculation result of the energy band structure of the heterostructure produced by sequentially depositing the cladding layers of _1-y (y = 0.06) is shown in Fig. 1 (b). , That is, the refractive index distribution.

The energy band is the well-known LCAO (Line
ar Combination of Atomic Orbital) method. It is assumed that the GaAs substrate and the cladding layer have the same lattice constant, and the active layer is distorted by the in-plane compressive stress to maintain the lattice coherency with the cladding layer.

Referring to FIG. 1A, first, the energy at the upper end of the valence band of each deposited layer in the above structure is determined by LCAO.
Calculated by the method. Next, the energy at the bottom of the conduction band of each deposited layer was calculated by adding the forbidden band width of each deposited layer to the top energy of the valence band. The forbidden band width of the substrate and the clad layer was obtained by using the value of the single crystal without strain, and the forbidden band width of the active layer was obtained by adding the effect of strain to the value of the single crystal without strain.

According to this calculation, the energy at the upper end of the valence band of the cladding layer is 0.96 eV lower than that of the substrate and 1.09 eV lower than that of the active layer. On the other hand, the energy at the bottom of the conduction band of the clad layer is 0.19 eV from the substrate and 0.36 eV from the active layer.
eV becomes higher. That is, the conduction band offset energy between the clad layer and the active layer is 0.36 eV.

This conductor offset energy, 0.36
eV is 0.17 eV for the conventional GaAs clad layer
It is larger by about 0.19 eV and is almost equal to the conduction band offset energy in the case of the InGaP cladding layer. Therefore, the semiconductor light emitting device to which this configuration is applied has a characteristic temperature equal to or higher than that of the conventional example.

Regarding the light confinement effect, the larger the difference Δn in refractive index between the cladding layer and the active layer, the higher the light confinement effect. II-V as described above with reference to FIG.
ZnCdSSe or ZnSSe which is a group I compound semiconductor
Has a refractive index of about 2.6, which is considerably smaller than the refractive index of about 3.2 with the active layer made of a III-V group compound semiconductor. Therefore, the difference Δn in the refractive index between the cladding layer and the active layer
Is about 0.6.

On the other hand, in the conventional light emitting device using the III-V group compound semiconductor as the cladding layer, Δn is 0.1 to 0.
Only 2 orders. Therefore, in the configuration of the present invention in which Δn is large, the light confinement is effectively performed, and the light emitting efficiency of the semiconductor light emitting device to which this is applied is significantly superior to the conventional device.

The above results show that the cladding layer is made of Zn _1-x C
d _x S _y Se _1-y (0 ≦ x ≦ 0.5) and the active layer is I
The same applies to the case of using nGaAsP or InGaAs. It should be noted that y is usually, when the cladding layer and active layer are epitaxially deposited on the substrate described below,
The lattice constant of the clad layer is determined to be the same as that of the substrate. Therefore, the degree of freedom in selecting the substrate is large,
The element design is easy.

In the second configuration of the present invention, the semiconductor light emitting device
In order to apply the usual manufacturing process of
The epitaxial layer is epitaxially deposited. Epitaxial deposition
In order to prevent crystal defects from occurring in the clad layer,
Limit the difference in lattice constant between the substrate and the cladding layer to within a certain value.
There must be. Therefore, for example, on a GaAs substrate
ZnS having a composition in which the lattice constant is substantially the same as that of the substrate_0.06Se _0.94
Deposit a clad layer. The clad layer with such composition
Is In_0.5Ga_{0. Five}Light in the 1.3 μm band on the As active layer
Appropriate strain to release. Therefore, in this configuration,
General semiconductor laser manufacturing method by epitaxy
, The strained semiconductor of the desired wavelength band, for example, 1.3 μm band
Body lasers can be manufactured.

It should be noted that the larger the S content of the ZnSSe cladding layer, the smaller its lattice constant and the higher strain applied to the active layer.
The conductor offset energy between the clad layer and the active layer is large, which is preferable from the viewpoint of temperature characteristics. On the other hand, S is 0.
If it is more than 06, the difference in lattice constant from the substrate becomes large and defects are introduced, so the amount of S is limited.

As already mentioned in the first configuration, ZnCdSSe can be used in the cladding layer in order to relax the restrictions resulting from matching with the lattice constant of such a substrate. By mixing Cd, the lattice constant of the cladding layer can be widely changed, and the lattice matching with the substrate becomes easy. Further, in order to keep the difference in lattice constant between the clad layer and the active layer at an appropriate value, the active layer can be made of InGaAsP.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to embodiments of a double heterostructure stripe semiconductor laser.

With reference to FIG. 2, an n-type GaAs layer is deposited as a buffer layer 2 on an n-type GaAs substrate 1. Then, an n-type ZnS _0.06 Se _0.94 layer is deposited as the cladding layer 3. Then, for example, non-doped In with a thickness of 10 nm
_{A 0.5} Ga _0.5 As layer is deposited as the active layer 4. Then, a p-type ZnS _0.06 Se _0.94 layer is deposited as the cladding layer 5, and a p ⁺ -type GaAs layer is further deposited as the contact layer 6. These deposition layers are deposited by, for example, MBE (Molecular Beam Epitaxy).

Here, the composition of the cladding layer is selected so that the lattice constant of the cladding layer substantially matches the lattice constant of the substrate. Next, the stripe electrode 7 is formed on the contact layer 6.
A lower electrode is formed on the back surface of the substrate 1. Finally, the substrate 1 is cleaved in the direction perpendicular to the stripe electrode 7 to form an optical resonator having the cleaved surface as a reflection surface, and a stripe type semiconductor laser having a high strain active layer is manufactured.

The energy band diagram and the refractive index distribution of the semiconductor laser of this embodiment are shown in FIG. Referring to FIG. 1, the semiconductor light emitting device of this embodiment has a large conduction band offset energy and a high characteristic temperature. In addition, the difference in refractive index is large and the luminous efficiency is high. Therefore, it is possible to obtain a semiconductor laser with high conversion efficiency and small characteristic variation due to temperature. Although this embodiment relates to a laser, it can be applied to a light emitting element having an active layer and a cladding layer, for example, a light emitting diode.

[0031]

As described above, according to the present invention, InG
ZnCd which is a II-VI group compound semiconductor is used as a cladding layer of a semiconductor light emitting device having an active layer of aAs or InGaAsP.
Since SSe or ZnSSe is used, the difference in the refractive index between the cladding layer and the active layer and the conduction band offset energy are increased, so that it is possible to provide a semiconductor light emitting device having high conversion efficiency and high characteristic temperature. Therefore, it greatly contributes to the performance improvement of the semiconductor light emitting device.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

FIG. 2 is a sectional view of an embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2 buffer layer 3,5 clad layer 4 active layer 6 contact layer 7 stripe electrode 8 lower electrode

Claims (2)

[Claims] 1. A semiconductor light-emitting device having an active layer (4) and cladding layers (3, 5) sandwiching the active layer (4), wherein the active layer (4) is made of InGaAs or InGaAsP. And the cladding layers (3, 5) are
A semiconductor light emitting device comprising ZnSSe or ZnCdSSe. 2. The semiconductor light emitting device according to claim 1, wherein GaAs is used as the substrate (1), and the cladding layer (3) is used.
5) is made of ZnSSe deposited on the substrate (1), and the active layer (4) has a lattice constant different from that of the cladding layers (3, 5) deposited on the cladding layer (3). A semiconductor light-emitting device comprising InGaAs.