JPH0541562A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE:To enable manufacture of a high quality Al group laser by utilizing a InGaAlAsP guide layer in a InGaAs/InGaAlAsMQW laser. CONSTITUTION:An n-type clad layer (a first semiconductor layer) 2, a guide layer (a second semiconductor layer) 12, an active layer (a third semiconductor layer) 4, a guide layer (a fourth semiconductor layer) 11, a p-type clad layer (a fifth semiconductor layer) 6 and a p-type electrode layer (a sixth semiconductor layer) 7 are formed in this sequentially on an n-type InP semiconductor substrate 1. The third semiconductor 4 has a multiquantum well (MQW) structure having a In(1-x-y)GaxAlyAs quantum well layer (0<=x, y<=1) and a In(1-x-y) GaxAlyAs barrier layer (0<=x, y<=1) in multilayer. Moreover, the second and fourth semiconductor layers 11, 12 are formed of an In(1-u)GauAs(1-v)Pv semiconductor layer (0<=u, v<=1). Thereby, a high quality semiconductor light emitting element which can easily realize DFB such as a InGaAs/InGaAlAs type laser can be realized.

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 as a semiconductor light source used in the field of long wavelength optical fiber communication, and more particularly to an InGaAsP guide layer and InGa.
The present invention relates to a ridge type semiconductor laser having an As / InAlAsMQW active layer or a DFB-MQW semiconductor laser having a ridge structure having an InGaAsP guide layer and an InGaAs / InAlAsMQW active layer in which a diffraction grating is formed.

[0002]

2. Description of the Related Art In recent years, research on a multiple quantum well (MQW) structure laser has been activated for the purpose of improving the performance of a semiconductor laser for optical fiber communication. Among them, InGaAs
/ InGaAsP-based MQW laser and InGaAs /
Two systems of InGaAlAs based MQW lasers have been the main research subjects. Especially InGaAs / InGaAlA
The s-series MQW laser has the following features as compared with the InGaAs / InGaAsP-series laser.

(1) The discontinuity ΔEc of the conduction band is large (0.5 eV), and a remarkable quantum effect can be expected. Therefore, it is possible to realize excitons in the quantum well and a laser with a new function utilizing the resonant tunneling effect. Further, due to the large quantum effect, improvement of the spectrum width and relaxation oscillation frequency can be expected.

(2) Since the discontinuity ΔEv of the valence band is small (0.2 eV), the pile-up effect of holes can be reduced. This is advantageous in realizing high speed modulation and the like.

The InGaAs / InGaAlAs system has the characteristics as described above, and the conventional structure has the following problems.

(1) In the conventional structure, InAl is formed in the cladding layer.
The As layer or the InGaAlAs layer was used.
However, when the clad layer is a mixed crystal, it is easily affected by lattice misalignment and the thermal resistance becomes large. To solve this problem, we have already proposed a structure using InP for the cladding layer. That is, it is as disclosed in Japanese Patent Application Laid-Open No. 61-32590 entitled "Quantum well semiconductor laser and manufacturing method thereof" by the same applicant as the present application. This eliminates the effect of lattice irregularity,
The thermal resistance could be reduced. However, the conventional structure has the following problems.

(2) In the conventional structure, InGaA is used as the guide layer.
The lAs layer was used. FIG. 6 is a schematic sectional structural view of a ridge type semiconductor laser having a conventional structure. In the figure, 1 is an n-type InP substrate, 2 is an n-type InP substrate
Cladding layer, 3 InGaAlAs guide layer, 4 In
GaAs / InAlAs MQW active layer, 5 is InGaA
1As guide layer, 6 is a p-type InP clad layer, and 7 is a p-type InGaAs electrode layer. 8 is a SiO ₂ film, 9 is an n-type electrode, and 10 is a p-type electrode. However, when the InGaAlAs layer is used as the guide layer, the quality of the MQW layer grown thereon tends to deteriorate, and the oscillation threshold value tends to increase. In the case of producing a DFB-MQW structure or the like, it is necessary to form a diffraction grating in the guide layer, but InG
Re-growth on the aAlAs layer is extremely difficult.

[0008]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above problems in the prior art, to provide a high quality and DF
It is to realize a semiconductor light-emitting device such as an InGaAs / InGaAlAs-based laser which is easily converted to B.

[0009]

The constitution of the present invention is as follows. That is, according to the present invention, a first semiconductor layer (2) having a first conductivity type that serves as a cladding layer and a second semiconductor layer that serves as a guide layer are formed on an InP semiconductor substrate (1) having a first conductivity type. (12), a third semiconductor layer (4) serving as an active layer, a fourth semiconductor layer (11) serving as a guide layer,
A semiconductor light emitting device having a structure in which a fifth semiconductor layer (6) having a second conductivity type that serves as a clad layer and a sixth semiconductor layer (7) having a second conductivity type that serves as an electrode layer are sequentially stacked. In, the third semiconductor layer (4) to be the active layer is In
_(1-xy) Ga _x Al _y As quantum well layer (0 ≦ x, y ≦
1) and In _(1-XY) Ga _X Al _Y As barrier layer (0 ≦
Second and fourth semiconductor layers (11, 12) each having a multi-quantum well structure in which (X, Y ≦ 1) are stacked and serve as guide layers.
In _(1-u) Ga _u As _(1-v) P _v semiconductor layer (0 ≦ u,
v ≦ 1), and has a structure as a semiconductor light emitting device.

Alternatively, the present invention provides a first conductivity type I.
On the nP semiconductor substrate (1), a first semiconductor layer (2) having a first conductivity type that serves as a cladding layer, a second semiconductor layer (12) that serves as a guide layer, and a third semiconductor layer that serves as an active layer. Semiconductor layer (4) and a fourth semiconductor layer (13) serving as a guide layer
A semiconductor having a structure in which a fifth semiconductor layer (14) having a second conductivity type that serves as a clad layer and a sixth semiconductor layer (7) having a second conductivity type that serves as an electrode layer are sequentially stacked. In the light emitting device, the third semiconductor layer (4) serving as an active layer is I
n _(1-xy) Ga _x Al _y As quantum well layer (0 ≦ x, y ≦
1) and In _(1-XY) Ga _X Al _Y As barrier layer (0 ≦
The second semiconductor layer (12), which is a multi-quantum well structure in which X, Y ≦ 1) are laminated, and which serves as a guide layer, is made of In _(1-u) Ga.
_u As _(1-v) P _v semiconductor layer (0 ≦ u, v ≦ 1), and a fourth semiconductor layer (13) serving as a guide layer is formed into a diffraction grating In _(1-u) Ga _u As _{( 1-v)} P _v semiconductor layer (0 ≦
u, v ≦ 1), and the fifth semiconductor layer (14) having the second conductivity type serving as the clad layer is a regrown InP layer. is there.

[0011]

Embodiments of the present invention will now be described in detail with reference to the drawings. In the present embodiment in the case of a laser MQW layer is composed of _{In (1-y) Al y} As barrier _{layer, In (1-x) Ga} x As quantum well layer (0 <x, y <1 ),
The case of using an n-type substrate will be described below.
_(1-xy) Ga _x Al _y As barrier layer, quantum well layer (0 <
It goes without saying that the present invention can also be applied to the case of x, y <1) and the case of a p-type substrate. Furthermore, in the embodiments of the present invention, the case of using the InP substrate will be limitedly described, but it is obvious that a substrate made of another semiconductor material, for example, a GaAs substrate or a Si substrate may be used.

FIG. 1 is a schematic sectional structural view of a ridge type semiconductor laser as an embodiment of the present invention.
The laser structure was manufactured using the gas source MBE method. In FIG. 1, 1 is an n-type InP substrate, 2 is an n-type InP cladding layer, 11 and 12 are InGaAsP guide layers, 4 is an InGaAs / InAlAsMQW active layer, and 6 is a p-type I.
The nP clad layer 7 is a p-type InGaAs electrode layer.
8 is a SiO ₂ film, 9 is an n-type electrode, and 10 is a p-type electrode. The MQW active layer has a quantum well width of 80Å and a barrier width of 3
It was 0Å, and the MQW layer had 6 periods. The n-type and p-type doping concentrations are 1 × 10 ¹⁸ cm ⁻³ . In the structure of the embodiment of the present invention shown in FIG. 1, the quality of the MQW active layer is improved as compared with the case where the InGaAlAs guide layer having the conventional structure shown in FIG. It is advantageous for lowering the threshold value. Also, the guide layer is A
Since l is not included, the regrowth of the cladding layer after forming the diffraction grating is easy, and the DFB laser can be formed.

FIG. 2 is a comparison of the cavity length dependence of the oscillation threshold current density of the laser of the conventional structure having the InGaAlAs guide layer (FIG. 6) and the laser of the structure of the present invention having the InGaAsP guide layer (FIG. 1). is there. As is clear from the figure, the laser of the present invention having the InGaAsP guide layer has a lower oscillation threshold. FIG. 3 shows current / light output characteristics in room temperature CW operation of a ridge type semiconductor laser having an InGaAsP guide layer according to an embodiment of the present invention. The oscillation threshold value is 20 mA, which is extremely low for a ridge type semiconductor laser. The differential quantum efficiency was 0.21 W / A, which was good. From these results, by using the InGaAsP guide layer, high quality InGaAs / InAlAs
It can be seen that an MQW laser is obtained.

FIG. 4 shows a ridge structure DFB-MQW semiconductor laser as a second embodiment of the present invention, which is manufactured by forming a first-order diffraction grating on the InGaAsP guide layer 13 and re-growing the InP cladding layer 14. It is a thing. In the figure, 1 is an n-type InP substrate, 2 is an n-type InP cladding layer, 12 is an InGaAsP guide layer, and 4 is InGaAs.
/ InAlAsMQW active layer, 13 is an InGaAsP guide layer in which a diffraction grating is formed, and 14 is regrown p-type In
The P clad layer 7 is a p-type InGaAs electrode layer. 9
Is an n-type electrode, and 10 is a p-type electrode. The MQW active layer has a quantum well width of 80 Å and a barrier width of 30 Å, and the MQW layer has 6 periods. The doping concentration of n-type and p-type is 1 ×
It is 10 ¹⁸ cm ^-3 . The regrown layer was also grown by the gas source MBE method.

FIG. 5 shows an oscillation spectrum at room temperature of an InGaAs / InAlAsDFB-MQW laser manufactured as a second embodiment of the present invention. Oscillation wavelength is 1.5
It is 4 μm, and it can be seen that oscillation is performed in a single mode with a side mode ratio of 30 dB or more. The oscillation threshold is 25
It was mA.

[0016]

As described in detail above, InGaA
InGaA in s / InGaAlAs MQW laser
By using the sP guide layer, a very high quality A
An l-system laser can be manufactured. Moreover, it is easy to make DFB. Therefore, it can be said that the laser of the present invention can be an important device for future optical communication systems. In the embodiments of the present invention, the description has been limited to the InP substrate, but it is clear that the same effect can be obtained by using other semiconductor materials such as GaAs substrate or Si substrate.

[Brief description of drawings]

FIG. 1 is a schematic sectional structural view of a ridge type semiconductor laser as a first embodiment of the present invention.

FIG. 2 is a comparison diagram of the cavity length dependence of the oscillation threshold current density of a laser having a conventional structure having an InGaAlAs guide layer (FIG. 6) and a laser having a structure of the present invention having an InGaAsP guide layer (FIG. 1).

FIG. 3 is a diagram showing current / light output characteristics in room temperature CW operation of a ridge type semiconductor laser having an InGaAsP guide layer according to an example of the present invention.

FIG. 4 is a ridge structure D according to a second embodiment of the present invention.
FIG. 3 is a schematic cross-sectional structure diagram of an FB-MQW semiconductor laser.

FIG. 5 is an oscillation spectrum diagram of an InGaAs / InAlAsDFB-MQW semiconductor laser at room temperature.

FIG. 6 is a schematic cross-sectional structure diagram of a ridge type semiconductor laser having a conventional structure having an InGaAlAs guide layer.

[Explanation of symbols]

1 n-type InP substrate 2 n-type InP clad layer 3,5 InGaAlAs guide layer 4 InGaAs / InAlAsMQW active layer 6 p-type InP clad layer 7 p-type InGaAs electrode layer 8 SiO ₂ film 9 n-type electrode 10 p-type electrode 11, 12 InGaAsP guide layer 13 InGaAsP guide layer having a diffraction grating 14 Regrown p-type InP clad layer

Claims (2)

[Claims] 1. On an InP semiconductor substrate of the first conductivity type,
A first semiconductor layer having a first conductivity type that serves as a clad layer, a second semiconductor layer that serves as a guide layer, a third semiconductor layer that serves as an active layer, and a fourth semiconductor layer that serves as a guide layer. A semiconductor light emitting device having a structure in which a fifth semiconductor layer having a second conductivity type serving as a clad layer and a sixth semiconductor layer having a second conductivity type serving as an electrode layer are sequentially stacked. The third semiconductor layer is In _(1-xy) Ga _x Al _y A
s quantum well layer (0 ≦ x, y ≦ 1) and In _(1-XY) Ga
Second and fourth guide layers, each having a multi-quantum well structure in which _X Al _Y As barrier layers (0 ≦ X, Y ≦ 1) are stacked.
The semiconductor layer _{In (1-u) Ga u} As (1-v) P v semiconductor layer (0 ≦ u, v ≦ 1 ) and to the semiconductor light emitting element characterized by the. 2. On the InP semiconductor substrate of the first conductivity type,
A first semiconductor layer having a first conductivity type that serves as a clad layer, a second semiconductor layer that serves as a guide layer, a third semiconductor layer that serves as an active layer, and a fourth semiconductor layer that serves as a guide layer. A semiconductor light emitting device having a structure in which a fifth semiconductor layer having a second conductivity type, which serves as a clad layer, and a sixth semiconductor layer having a second conductivity type, which serves as an electrode layer, are sequentially stacked. The third semiconductor layer is In _(1-xy) Ga _x Al _y A
s quantum well layer (0 ≦ x, y ≦ 1) and In _(1-XY) Ga
_X Al _Y As barrier layers (0 ≦ X, Y ≦ 1 ) becomes a multiple quantum well structure obtained by stacking the second semiconductor layer serving as a guide layer _{In (1-u) Ga u} As (1-v) P _v Semiconductor layer (0 ≦ u,
v ≦ 1), and the fourth semiconductor layer serving as a guide layer is an In _(1-u) Ga _u As _(1-v) P _v semiconductor layer (0 ≦ u, v ≦ 1) in which a diffraction grating is formed, A semiconductor light-emitting device, wherein the fifth semiconductor layer having the second conductivity type and serving as a clad layer is a regrown InP layer.