JPH03263891A - Semiconductor light-emitting element - Google Patents

Abstract

PURPOSE:To prevent light which is generated secondarily by light entering from an activation layer to a clad layer or light entering from a clad layer to the outside layer from returning to the activation layer by including a reflection-preventing film between the clad layer and the semiconductor layer and by reducing reflection of naturally radiated light from the clad layer toward the semiconductor layer drastically. CONSTITUTION:A clad layer 2, a reflection-preventing film 3, and a next semiconductor layer 4 which are in contact with an activation layer in sequence are constituted by lamination and the reflection-preventing film 3 is thick enough so that it is substantially transparent to the light emitted the activation layer 1, its reflection index is larger than that of the clad layer 2, and reflection for the emitted light is minimum at a proper angle where an incidence angle from the clad layer 2 is equal to or larger than 60 deg.. Then, the reflection index of the semiconductor layer 4 is larger than that of the reflection-preventing film 3. Also, the reflection index of the semiconductor layer 4 is larger than that of the clad layer 2 and a non-luminous recombination center is doped.

Description

[Detailed Description of the Invention] (Summary) Regarding semiconductor light emitting devices such as semiconductor lasers, in order to reduce heat generation in the active layer, light that enters the cladding layer from the active layer and light that enters the outer layer from the cladding layer is used to reduce heat generation in the active layer. The present invention proposes first to third semiconductor light-emitting devices for the purpose of suppressing light that is secondarily generated by the light from returning to the active layer,
The first semiconductor light emitting device has a laminated structure of a cladding layer, an antireflection film, and a next semiconductor layer that are in contact with an active layer in sequence, and the antireflection film is substantially equal to the emission wavelength of the active layer. It is transparent and has a refractive index higher than that of the cladding layer, and has a thickness that minimizes the reflection of the emission wavelength at an appropriate angle of incidence from the cladding layer of 60° or more, and has a thickness that is next to the antireflection film. The semiconductor layer is configured to have a higher refractive index than the antireflection film, and the second semiconductor light emitting device has a laminated structure of a cladding layer sequentially in contact with an active layer and a semiconductor layer next to the cladding layer, The semiconductor layer next to the cladding layer is configured to have a larger refractive index than the cladding layer and is doped with non-radiative recombination centers, and the third semiconductor light emitting device is configured such that the semiconductor layer next to the cladding layer has a larger refractive index than the cladding layer and is doped with non-radiative recombination centers. The anti-reflective film has a laminated structure of a layer, an anti-reflective film, and the next semiconductor layer, and the anti-reflective film corresponds to the anti-reflective film 3 of the first semiconductor light emitting element, and The semiconductor layer is configured to be similar to the semiconductor layer next to the cladding layer of the second semiconductor light emitting device.

[Industrial application field]

The present invention relates to a semiconductor light emitting device such as a semiconductor laser,
In particular, the present invention relates to a configuration that reduces heat generation in the active layer.

Semiconductor lasers are used as light sources in optical disk devices, optical communication systems, etc., and increases in the temperature of the active layer, which is the light emitting region, have a negative effect on characteristics such as threshold current (I). It is important to reduce heat generation.

[Conventional technology]

One of the mechanisms by which the active layer generates heat is that the active layer itself reabsorbs spontaneously emitted light generated in the active layer. The reabsorbed light includes light that enters the cladding layer from the active layer and returns to the active layer by reflection within the cladding layer, and electrons generated by light that enters the outer layer from the cladding layer and is absorbed. A pair of holes emits light that returns to the active layer, and this light promotes heat generation in the active layer.

Especially GaAs/AlG lattice matched to GaAs substrate
In an a1nP laser, compared to a GaAs/AlGaAs laser or an InP/InGaAsP laser, the temperature of the active layer increases significantly due to the high thermal resistance of the cladding layer. This temperature increase has an adverse effect on characteristics such as threshold current (I) in the laser.

However, in conventional lasers, little effort has been made to reduce heat generation in the active layer in order to alleviate this temperature rise.

[Problem to be solved by the invention]

In order to reduce heat generation in the active layer in a semiconductor light emitting device such as a semiconductor laser, the present invention aims to reduce heat generation in the active layer by using light that enters the cladding layer from the active layer and light that enters the outer layer from the cladding layer. The purpose is to suppress the generated light from returning to the active layer.

[Means to solve the problem]

FIGS. 1(a) to 1(C) are diagrams explaining the principle of the present invention.

Referring to FIG. 1(a), the above object has a laminated structure of a cladding layer 2, an antireflection film 3, and a semiconductor layer 4 next to the active layer 1, and the antireflection film 3 has the following structure: The active layer 10 is substantially transparent to the emission wavelength, has a refractive index greater than that of the cladding N2, and has a thickness that minimizes reflection for the emission wavelength at an appropriate angle of incidence from the cladding layer 2 of 60° or more. , the semiconductor layer 4 is achieved by the first semiconductor light emitting device of the present invention having a larger refractive index than the antireflection film 3.

Further, with reference to FIG. 1(b), it has a laminated structure of a cladding layer 2 sequentially in contact with an active layer 1 and a semiconductor Ji4a next thereto, and the semiconductor N4a has a refractive index larger than that of the cladding layer 2 and This is achieved by a second semiconductor light emitting device of the present invention in which non-radiative recombination centers are doped.

Furthermore, with reference to FIG. 1(C), a cladding layer 2, an antireflection film 3, and a semiconductor layer 4a next to the active layer 1 are sequentially in contact with the active layer 1.
The anti-reflection film 3 is similar to the anti-reflection film 3 of the first semiconductor light emitting device, and the semiconductor layer 4a is similar to the semiconductor layer 4a of the second semiconductor light emitting device. This is achieved by the third semiconductor light emitting device of the present invention.

(Function) In the first semiconductor light emitting device, the semiconductor layer 4 corresponds to the substrate or contact layer next to the cladding layer in a conventional laser, and is interposed between the cladding layer 2 and the semiconductor layer 4. The anti-reflection film 3 having the above-mentioned structure significantly reduces the reflection of spontaneously emitted light directed from the cladding layer 2 toward the semiconductor layer 4, as will be described later.

For this reason, most of the light that has entered the cladding layer 2 from the active layer 1 is prevented from passing through the semiconductor layer 4 and returning to the active layer 1.

In the second semiconductor light emitting device, the non-light-emitting coupling center prevents light from being generated secondarily due to light entering the semiconductor layer 4a from the cladding layer 2. This effectively suppresses the light from returning to the active layer 1.

The third semiconductor light emitting device has the function used in the first semiconductor light emitting device and the second semiconductor light emitting device to suppress light returning to the active layer 1.
This device combines both of the functions used in the semiconductor light emitting device. This makes it possible to suppress both the return from the cladding 512 and the return from the semiconductor layer 4a.

[Examples] Examples of the present invention will be described below with reference to FIGS. 2 to 5. FIG. 2 is a cross-sectional view perpendicular to the light emission direction of the first embodiment, FIGS. 3(a) and 3(b) are diagrams explaining the effect of the antireflection film in the first embodiment, and FIG. 4 is a cross-sectional view of the second embodiment. FIG. 5 is a sectional view perpendicular to the light emission direction of the third embodiment.

The first embodiment shown in FIG. 2 is a semiconductor laser corresponding to the first semiconductor light emitting device described above, and is an example in which the current confinement structure is constituted by a diffusion region.

In the same figure, 11 is an InGaP active layer with a thickness of 0.1 μm, and 12a
is n4AIx Gap-x )o, 5lno, sP (
xJ, 7) Cladding layer, 1μ thick rust, 13a is n-(Alx Gap-++)e, 5lno
, sP (x=0.1) anti-reflection film, thickness 1200, 14 is n-GaAs substrate, width about 300 pm, 1
2b is p-(A1.Gap-x)o,5rno,s
P (x=0.7) cladding layer, thickness 1μ-5 13b is p-(Alx Gap-x)o, 5lno,
sP (x=0.1) anti-reflection coating, thickness 1200, 15 is p-GaAs contact layer, thickness 1 μm, 1
6 is a Zn diffusion region constituting a current confinement structure, width 5μ
m, depth 1.2 μm, 17a is an n-side electrode, 17b is an n-side electrode, active layer 11 + cladding layer 12a + antireflection film 1
3a + substrate 14, active layer 11 + cladding layer 12b + antireflection 1] 1113b + contact layer 15, respectively, constitute the laminated structure described in the first semiconductor light emitting device.

The thickness of the antireflection films 13a and 13b was set to 1200 on the basis of the following data.

That is, in FIG. 3(a), spontaneous emission light (wavelength λ-6700) generated in the active layer 11 is transmitted to the cladding F112a (12
Incident angle θ at the cladding layer 12a (12b) interface when going from b) to the substrate 14 (contact layer 15)
shows the relationship between reflectance and reflectance. A is an antireflection film 13a (13
b) is absent, and the reflectance in that case is the incident angle θ
is 0.04 or less when the value increases from Oo to approximately 50'', and increases rapidly when the value exceeds 60''.

In addition, Figure 3 b) shows the relationship between the thickness of the anti-reflection film 13a (13b) and the reflectance at the incident angle θ = 80° where the reflectance is large in the absence of the anti-reflection film 13a (13b), The reflectance is at its minimum when the thickness is around 1200 people.

B in FIG. 3(a) represents the antireflection film 13a.
This is when the thickness of (13b) is set to 1200 people.

In this case, the reflectance is 0.04 or less over the range of incident angle θ from 0 to 80'.

The inventor has developed this first embodiment and the antireflection 111 from it.
As a result of comparing the characteristics with the one in which 13a and 13b are removed (conventional example), the threshold current (I) of the first embodiment is about 20% smaller (the threshold current is smaller). Improvements in characteristics were observed, with changes due to environmental temperature being reduced by about 15% and maximum light output increasing by about 40%.Although it is difficult to directly measure this, this is due to the reduction in heat generation in the active layer mentioned earlier. This is thought to be due to

What I would like to particularly mention here is that even when the heat sink is provided on the side of the n-side electrode 17b (the side opposite to the substrate 14), heat generation due to light absorption by the substrate 14 occurs on both sides of the current confinement region. Since the heat is radiated to the heat sink through the heat sink and the width of both sides is large, the efficiency of this heat radiation is extremely high.

This point also applies to the second and third embodiments described below.

Next, a second embodiment shown in FIG. 4 is a semiconductor laser corresponding to the second semiconductor light emitting device described above, and is an example constructed with a current confinement structure or a Fuji type laser structure.

In the figure, 21 is an InGaP active layer with a thickness of 0.1μ, and 22a
is P-(All Ga+-x)o, 5rne, sP
(x=0.7) cladding layer, 1 μm thick, 24a is a Zn-doped p-
Inx Ga1-x P (x=0.5) light absorption layer, Z
n doping amount 2×10'''~IXIO''/d, thickness 0.
1μ■, 24 is a p-GaAs substrate with a width of approximately 300μ, 22b is an n-(Alx Ga+-x)o, 5Ino, sP with a convex stripe constituting a current confinement structure.
(xJ, 7) Cladding layer, width of stripe 5μM, thickness of one stripe region 1.0μ-, thickness 0.2μ on both sides of stripe, 25a is n-In doped with Si as a non-radiative recombination center , Ga1-XP (x=0.5) light absorption layer, Si doping amount 2X1. O″〜I XlO19/
c+1, thickness 0.11ex, 25b is p-Inx Ga1-x P doped with Zn as a non-radiative recombination center
(x□0.5) Light absorption layer/current confinement layer, Zn doping amount 2
Xl, 0" ~ IXIO"/d, thickness 0.7 μM
~26 is an n-GaAs contact layer, 1 μm thick,
27a is an n-side electrode; 27b is an n-side electrode;
a, active layer 21 + cladding layer 22b and optical absorption layer 25a
, 25b constitute the laminated structure described in the second semiconductor light emitting device.

As a result of comparing the characteristics of this second embodiment and one in which the light absorption layers 24a, 25a, and 25b are not doped with non-radiative recombination centers (conventional example), the inventor found that the second embodiment For example, the threshold current (1th) is about 13%
The change in threshold current due to environmental temperature is approximately 7
% and the maximum light output increased by about 20%.

Next, the third embodiment shown in FIG. 5 is a semiconductor laser corresponding to the third semiconductor light emitting device described above, and the current confinement structure is constituted by a ridge type laser structure as in the second embodiment. This is an example.

In the same figure, the same symbols as in FIG. 4 indicate the same objects, and 23a is p-(Alx Ga+-*)o, 5lno,
sP (x=0.1) antireflection film, thickness 1200, 23b is n-(Alx Ga+-x)o, 5lno,
sP (X=0.1) anti-reflection film, thickness 1200, active layer 21 + cladding layer 22a + anti-reflection film 2
3a, optical absorption layer 24a, active layer 21 + cladding layer 22
Each of the ten antireflection films 23b and the ten light absorption layers 25a is
It constitutes the laminated structure described in the third semiconductor light emitting device. In addition, the active layer 21 + the cladding 122b + the light absorption layer and current confinement layer 25b constitute the laminated structure described in the second semiconductor light emitting device.

The present inventor has developed this third embodiment and the antireflection film 2 from it.
3a, 23b and the light absorbing layers 24a and 25
As a result of comparing the characteristics of the third embodiment with those in which non-radiative recombination centers are not doped in a and 25b (conventional example), the threshold current (I) of the third embodiment is approximately 15% smaller; Improvements in characteristics were observed in that the change in threshold current due to environmental temperature was reduced by about 10% and the maximum light output was increased by about 25%.

It should be noted that the components and dimensions of each semiconductor layer are not limited to those in the examples, that the arrangement of the antireflection film shown in 13a etc. is arbitrary with respect to the upper and lower sides of the active layer, and that the thickness of the antireflection film is It is easy to understand from the above explanation that the incident angle θ is not limited to 80° and that the semiconductor layer doping the non-radiative recombination center can be placed arbitrarily above and below the active layer. be understood.

Furthermore, it is easy to see from the examples that a diffusion region or a solid-state laser structure can be arbitrarily adopted for the configuration of the current confinement structure in any of the semiconductor lasers corresponding to the first to third semiconductor light emitting devices. It can be analogized to

Further, the present invention is not limited to semiconductor lasers, but
Application to semiconductor light emitting diodes (LEDs) is also possible. In that case, it becomes possible to obtain a high-output, low-loss LED.

(Effects of the Invention) As explained above, according to the present invention, in order to reduce heat generation in the active layer in a semiconductor light emitting device such as a semiconductor laser, light entering the cladding layer from the active layer, It is possible to suppress the light that is secondarily generated by the light that has entered the outer layer from returning to the active layer, which has the effect of improving the characteristics of the semiconductor light emitting device.

[Brief explanation of drawings]

Figures 1 (a) to (C) are diagrams explaining the principle of the present invention, Figure 2 is a sectional view perpendicular to the light emission direction of the first embodiment, and Figures 3 (a) and (b) are the first embodiment. FIG. 4 is a sectional view perpendicular to the light emission direction of the second embodiment; FIG. 5 is a sectional view perpendicular to the light emission direction of the third embodiment. In the figure, 1.11.21 is the active layer, 2.12a, ! 2b, 22a, 22b are cladding layers, 3.13a, 13b, 23a, 23b are antireflection films, 4.4a is a semiconductor layer, 14 is a substrate corresponding to semiconductor layer 4, 15 is a contact layer and is semiconductor layer 4 Applicable to 24a, 25a
25b is a light absorption layer that corresponds to the semiconductor layer 4a, 25b is a light absorption layer and current confinement layer that corresponds to the semiconductor layer 4a, A is without antireflection film, B is with antireflection film, θ is the angle of incidence, . Figure 1 Figure 1 The 9th corner of the 8th direction is a vertical axial plane. Figure 2 The 8th direction of the 8th direction is the perpendicular axial plane. Figure 3: East map to explain the effectiveness of the 8ff and tsutsuma stand.

Claims (1)

[Scope of Claims] 1) It has a laminated structure of a cladding layer, an antireflection film, and a next semiconductor layer that are in contact with an active layer, and the antireflection film is:
A thickness that is substantially transparent to the emission wavelength of the active layer, has a refractive index greater than that of the cladding layer, and has a minimum reflection for the emission wavelength at an appropriate angle of incidence from the cladding layer of 60° or more. A semiconductor light emitting device, wherein the semiconductor layer next to the antireflection film has a refractive index greater than that of the antireflection film. 2) It has a laminated structure of a cladding layer sequentially in contact with an active layer and a next semiconductor layer, and the semiconductor layer next to the cladding layer has a refractive index larger than that of the cladding layer and has non-radiative recombination centers. A semiconductor light emitting device characterized in that it is doped. 3) It has a laminated structure of a cladding layer, an antireflection film, and a next semiconductor layer that are in contact with the active layer, and the antireflection film is:
A thickness that is substantially transparent to the emission wavelength of the active layer, has a refractive index greater than that of the cladding layer, and has a minimum reflection for the emission wavelength at an appropriate angle of incidence from the cladding layer of 60° or more. A semiconductor light emitting device, wherein the semiconductor layer next to the antireflection film has a refractive index larger than that of the antireflection film and is doped with non-radiative recombination centers.