JPH0870161A - Semiconductor light emitting element - Google Patents

Abstract

PURPOSE: To increase the carrier injection efficiency in an active layer by a method wherein the barrier layer of multiquantum well layer comprising a clad layer or light confinment layer is composed of III-V compound semiconductor layer having an indirect transition type band structure. CONSTITUTION: Clad layers 3, 7 are composed of a multiquantum well structure comprising AlAs0.4 Sb0.6 barrier layer and an InP well layer. Besides, an active layer 5 is composed of a multiquantum structure comprising an InP layer and an InGaAs well layer. Since the AlAs0.4 Sb0.6 comprising the barrier layer having an indirect transition type band structure 1 is further provided with about the same lattice constant of an InP substrate 1, the clad layers 3, 7 with few crystalline defects can be formed. Through these procedures, the carrier injection efficiency in the active layer 5 can be increased.

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 used for optical communication, optical information processing and the like.

[0002]

2. Description of the Related Art Conventionally, a quantum well structure is used for an active layer in order to improve the luminous efficiency of a semiconductor light emitting device or to reduce the threshold current in a semiconductor laser device. Furthermore, it has been confirmed that these characteristics are further improved by introducing strain into this quantum well structure. This is interpreted to be mainly due to a decrease in the density of states associated with the quantum size effect and an increase in the optical gain. However, the necessity of incorporating a quantum well structure in the cladding layer or the optical confinement layer in the light emitting device having the conventional structure has not been discussed so much. Recently, an example of improving the electron confinement effect by using a cladding layer having a multiple quantum well structure has been proposed (see Reference 1). Reference 1: Electronics Letters, vol.22, pp1008, 1986.

[0003]

However, the conventional semiconductor light emitting device using the quantum well structure in the active layer has the following problems. That is, in the active layer having the quantum well structure, the differential gain calculated from the modulation band does not increase as expected from theory as compared with the differential gain of the semiconductor laser device having the bulk type active layer. .
Further, the characteristic temperature of the active layer having the quantum well structure is not so much higher than that of the bulk type active layer.

Recently, it has been clarified both theoretically and experimentally that the above problems can be explained by the carrier transport phenomenon (see Reference 2). That is, it is necessary for the injected carriers to be transported in a wide optical confinement layer or cladding layer before being injected into the quantum well and the strained quantum well of the active layer. Therefore, when these wide optical confinement layers and cladding layers include a multi-quantum well structure, carriers are lost by recombination process when passing through the barrier layer forming the multi-quantum well structure. , The ratio of the number of carriers entering the quantum well of the active layer is small. As a result, the differential gain is reduced.

In this carrier transport phenomenon, if the injection efficiency into the active layer is ∝1 / χ, χ is approximately represented by the following equation. That is, χ≈1 + (B _o / B _i ) (τ _d / τ _e ) ≈1 + (B _o / B _i ) (V _o / V _i ) ... (1) where B _o and B _i is the recombination constant of the barrier layer (o) and the quantum well layer (i) of the multiple quantum well structure which respectively constitute the cladding layer or the optical confinement layer, and V _o and V _i are the barrier layer (o) and the quantum, respectively. Well layer (i)
, Τ _d and τ _e are the delay time until carriers are diffused and injected into the quantum well, and the heat dissipation time of carriers from the quantum well layer to the barrier layer. Normal,
In order to lower the threshold value and lower the loss (high efficiency), the total thickness of the quantum well layer is reduced to some extent, and the optical confinement layer thickness is increased to optimize the optical confinement coefficient.
This increases V _o / V _i . Therefore, equation (1)
Χ increases, and the efficiency of carrier injection into the active layer is significantly reduced. Further, since the time constant τ _e decreases with increasing temperature of the element, χ increases with increasing temperature and carrier injection efficiency decreases. The present invention eliminates the adverse effects of the carrier transport phenomenon described above and maximizes the quantum size effect, which is an inherent advantage of quantum wells. Reference 2: IEEE J. Quantum Electron., Vol.QE-28, No.1
0, pp. 1990.

[0006]

The present invention provides a semiconductor light emitting device that solves the above-mentioned problems. A quantum semiconductor device having a pair of optical confinement layers and a clad layer sandwiched between a group 3-5 compound semiconductor substrate is used. In a semiconductor light emitting device provided with an active layer having a well structure, at least one of the optical confinement layer and the cladding layer includes a multiple quantum well structure on at least one side forming a pair, and the barrier layer forming the multiple quantum well structure is It is characterized by comprising a 3-5 group compound semiconductor having an indirect transition type band structure lattice-matched to the substrate.

[0007]

As can be seen from the formula (1), one method of eliminating the adverse effects of the carrier transport phenomenon and increasing the injection efficiency is to decrease the recombination constant B _o in the barrier layer and decrease χ. It is to be. By the way, in principle, a 3-5 group compound semiconductor having an indirect transition type band structure has an extremely small radiative recombination probability as compared with the direct transition type, and therefore has a small recombination constant B _o . Therefore, as described above, the barrier layer of the multiple quantum well layer forming the cladding layer or the optical confinement layer has an indirect transition type band structure.
When it is made of the group-5 compound semiconductor layer, the efficiency of carrier injection into the active layer is improved.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view of an embodiment of a semiconductor light emitting device according to the present invention. In the figure, 1 is an n-InP substrate, 2 is an n-InP buffer layer, 3 is a cladding layer, 4 is an InP optical confinement layer, 5 is an active layer, 6 is an InP optical confinement layer, 7 is a cladding layer, 8 is AlAs. _The contact layer is _0.4 Sb _0.6 . FIG. 2 shows a band structure on the conductive band side in the vicinity of the active layer 5. The clad layers 3 and 7 are
11 layers of AlAs _0.4 Sb _0.6 barrier layers 3a, 7a and 1
It has a multiple quantum well structure composed of 0 layers of InP well layers 3b and 7b. The active layer 5 has a multiple quantum well structure including two InP barrier layers 5a and three InGaAsP well layers 5b. Each barrier layer 3a, 7
The thicknesses of a, 5a and the well layers 3b, 7b, 5b are as described in the drawing. Here, in the multiple quantum well structure formed in the cladding layers 3 and 7, the AlAs _0.4 Sb _0.6 barrier layers 3a and 7a are thicker as they get closer to the active layer 5, but this is because the average bandwidth is This is because it is increased as the layer 5 is approached, and favorable carrier injection is realized. In this embodiment, the barrier layer 3
The AlAs _0.4 Sb _0.6 constituting a and 7a have an indirect transition type band structure and a lattice constant similar to that of the InP substrate, so that the cladding layers 3 and 7 having few crystal defects are present.
Can be formed. In the conventional structure, χ shown in the formula (1) is as large as 2-3, but in the present embodiment, χ is 1.
It can be 5 or less. Therefore, the carrier injection efficiency 1 / χ is improved to 2 to 3 times that of the conventional case, and the differential gain is also increased to 2 to 3 times as much as the conventional case. As the 3-5 group compound semiconductor having an indirect transition type band structure which constitutes the barrier layer, AlAs _0.4
Besides Sb _0.6 , it is also possible to use GaP, AlAs, AlSb, etc. which are lattice-matched to a GaAs substrate, a sapphire substrate or the like. Further, the structure of the multiple quantum well structure is not limited to the structure of the above embodiment.

[0009]

As described above, according to the present invention, 3
In a semiconductor light-emitting device in which an active layer having a quantum well structure sandwiched between a pair of optical confinement layers and a clad layer is provided on a Group-5 compound semiconductor substrate, at least one of the optical confinement layers and the clad layers has at least a pair. Since a barrier layer that includes a multiple quantum well structure on one side of the device and the barrier layer that constitutes the multiple quantum well structure is made of a Group 3-5 compound semiconductor having an indirect transition type band structure lattice-matched to the substrate, carriers to the active layer are formed. There is an excellent effect that the injection efficiency is improved and a low threshold and high efficiency semiconductor light emitting device can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an embodiment of a semiconductor light emitting device according to the present invention.

FIG. 2 is a diagram showing a band structure on a conductive band side in the vicinity of an active layer in the above-mentioned embodiment.

[Explanation of symbols]

 1 substrate 2 buffer layer 3, 7 clad layer 3a, 5a, 7a barrier layer 3b, 5b, 7b well layer 4, 6 optical confinement layer 5 active layer 8 contact layer

Claims (1)

[Claims] 1. A semiconductor light-emitting device comprising an active layer having a quantum well structure sandwiched between a pair of optical confinement layers and a cladding layer on a Group 3-5 compound semiconductor substrate, wherein at least the optical confinement layers and the cladding layers are provided. One includes a multiple quantum well structure on at least one side forming a pair, and the barrier layer forming the multiple quantum well structure is made of a Group 3-5 compound semiconductor having an indirect transition type band structure lattice-matched with the substrate. A semiconductor light-emitting device characterized by.