JPH0799365A - Semiconductor laser element using - Google Patents

Abstract

PURPOSE:To facilitate the formation of a semiconductor mixed crystal composition by a method wherein the quantum well layers of super-lattice layers, which are close to an active layer, are formed of a III-V mixed crystal semiconductor containing arsenic only as a group V constituent element and the barrier layers of the super-lattice layers are formed of a III-V mixed crystal semiconductor containing phosphorus only as a group V constituent element. CONSTITUTION:Quantum well layers 3a and 7a of n-type and p-type super-lattice layers 4 and 8, which are close to an active layer 6, are formed of a III-V mixed crystal semiconductor containing arsenic only as a group V constituent element. Barrier layers 3b and 7b are formed of a III-V mixed crystal semiconductor containing phosphorus only as a group V constituent element. The layer thicknesses of the layers 3a and 7a in the layers 4 and 8 are continuously changed. Thereby, the control of a semiconductor mixed crystal composition can be realized without difficulty.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device.

[0002]

2. Description of the Related Art In order to improve the characteristics of a semiconductor laser, it is important to have both a function of confining carriers (electrons and holes) and a function of confining light. A double hetero structure and a quantum well structure in which carriers are confined to a thickness of about de Broglie wavelength are effective for carrier confinement. On the other hand, in order to confine light, a confinement structure having a spatial spread of about the wavelength is required. Therefore, SC that confine light separately from the quantum well structure
H (separated optical confinement heterostructure
) Structure has been proposed, and GRIN (graded-refractiv
e-index) -SCH is effective.

However, the GRIN area is ternary or quaternary.
The original mixed crystal semiconductor is used, and its composition (forbidden band width or refractive index) must be continuously changed. Also, at the same time, it is usually necessary to perform lattice matching. Therefore, it is necessary to control the composition of the semiconductor mixed crystal with high precision, and precise control of the composition is relatively difficult. In order to solve the difficulty, a modified GRIN-S using a superlattice layer, which replaces a GRIN region requiring a continuous composition change with a superlattice structure.
CH was proposed.

A structure has been proposed in which an active layer and superlattice layers are arranged on both sides of the active layer, and a clad layer is arranged outside each superlattice layer ("SUPERLATICE OPTICAL-CAV").
ITYMULTIPLE-QUANTUM-WELL (SOC-MQW) LASERS GROWN BY
MOLECULAR-BEAM EPITAXY "ELECTRONICS LETTERS 12th A
pril 1984 Vol.20 No.8 pp.320-321, "MBE-grown InAs
/ GaInAs strained-layer MQW lasers with GaInAs / AlIn
As modified SCH structure "Inst. Phys. Conf.Ser. N
o 106: Chapter 10, Gallium arsenide and related com
pounds 1989). In these prior art examples, InAs is used for the quantum well layer of the superlattice layer, GaInAs is used for the barrier layer, and GaAs is used for the quantum well layer of the superlattice layer and AlGaAs is used for the barrier layer. As a result, the same refractive index change as GRIN can be realized by stacking two kinds of materials. However, GRIN-
The SCH structure is InGaAs / InA because of its ease of fabrication.
It is limited to As-based III-V group mixed crystal semiconductors such as 1As.

[0005]

In the III-V mixed crystal semiconductor system having arsenic and phosphorus as the V group constituent elements, the vapor pressure of the V group is higher than that of the III group, and therefore accurate control of the composition is compared. Deformation GRI using superlattice
The N-SCH structure has not been realized.

An object of the present invention is to use a superlattice having a III-V mixed crystal semiconductor having arsenic and phosphorus as V group constituent elements, which can broaden the selection range of oscillation wavelength to the short wavelength side and is easy to manufacture. The present invention is to provide a semiconductor laser device.

[0007]

To achieve this object, in a semiconductor laser device using a superlattice layer according to the present invention, a quantum well layer of a superlattice adjacent to an active layer contains only arsenic and a group V constituent element. II-group III-V mixed crystal semiconductor, and its barrier layer contains only phosphorus as a group V constituent element II
It has a structure characterized by being formed of a group IV mixed crystal semiconductor.

[0008]

[Embodiment 1] FIG. 1 shows the structure of a semiconductor laser device according to a first embodiment of the present invention. an n-type InGaP layer 2, which is an n-type cladding layer, on an n-type GaAs substrate 1,
n-type GaAs / InGaP superlattice layer 4, InGaAs /
A GaAs active layer 6, a p-type GaAs / InGaP superlattice layer 8, a p-type InGaP layer 9 which is a p-type cladding layer, and a p-type GaAs layer 10 which is a cap layer are laminated to form a semiconductor laser. Electrodes 101 and 102 for current injection are formed on the upper and lower surfaces. A semi-insulating InGaP layer 11 has a buried stripe structure for lateral mode control and current narrowing. The oscillation wavelength of this laser is 0.98 μm.

FIG. 2 shows the structure in the vicinity of the active layer of the same element corresponding to the portion 20 surrounded by the one-dot chain line in FIG. The superlattice layer 4 is formed by stacking 10 sets of an n-type GaAs quantum well layer 3a and an n-type InGaP barrier layer 3b, and the superlattice layer 8 is a p-type GaAs quantum well layer 7a and a p-type InGaP barrier layer 7b. Consisting of 10 sets of
The active layer 6 is composed of an InGaAs quantum well layer 5a and a GaAs barrier layer 5b. The InGaP barrier layers 3b and 7b have a constant layer thickness of 20Å, and the GaAs quantum well layers 3a and 7a have a layer thickness of 5Å to 50Å from the cladding layer toward the active layer.
And as shown in Figure 2, it is gradually increasing. As a result, the equivalent refractive index of the superlattice layers 4 and 8 is the InGaP cladding layer 2
It changes continuously from 3.4 in 9 to 3.6 in the active layer GaAs6. The effect is GRIN which changed composition continuously
Since it is equivalent to that of a layer and enables efficient optical confinement, the threshold current density is significantly reduced as compared with a device in which the superlattice layer is not inserted, and G is used instead of the superlattice layer.
It is at the same level as the element in which the RIN layer is inserted. In this embodiment, the layer thicknesses of the GaAs quantum well layers 3a and 7a in the superlattice layers 4 and 8 are continuously changed to have the same refractive index distribution as that of the GRIN structure.
Even when the layer thickness of 7a is constant, the threshold current density can be remarkably reduced.

[0010]

[Embodiment 2] FIG. 3 is a perspective view including a section taken along the line AA 'showing the structure of a semiconductor laser device according to a second embodiment of the present invention. FIG. 4 shows the structure in the vicinity of the active layer of the same element corresponding to the portion 30 surrounded by the one-dot chain line in FIG. The difference from the first embodiment is that the diffraction grating 12 formed of p-type GaAs is inserted between the p-type cladding layer 9 and the p-type superlattice layer 8 to realize the DFB structure. The oscillation wavelength of this laser is 0.98 μm, and it oscillates at a single wavelength. This diffraction grating utilizes the fact that GaAs and InGaP, which are one of the effects of the present invention, can be selectively chemically etched, and the GaA on the p-type superlattice layer 8 is utilized.
The s layer 12 is formed by forming a diffraction grating-like GaAs layer by the interference exposure method. The p-type clad layer 9 and the cap layer 10 are crystal-grown on it to form a semiconductor laser.
The buried stripe structure including the electrodes 101 and 102 and the semi-insulating InGaP layer 11 is the same as that in the first embodiment.
The oscillation characteristics of the DFB laser largely depend on the coupling coefficient determined by the depth of the diffraction grating 12 and the distance from the active layer 6. Using this structure and the fabrication method, the depth of the diffraction grating 12 is determined by the thickness of the GaAs layer, and the distance from the active layer 6 is determined by the layer thickness of the p-type superlattice 8. Therefore, the coupling coefficient is uncertain in the etching conditions. There are few factors that change with gender. as a result,
A DFB laser having a coupling coefficient as designed can be easily manufactured. The p-type and n-type superlattice layers 8 and 4 have the same structure as that of the first embodiment, and the effect thereof is that similar to the first embodiment, efficient light confinement is possible and the threshold current density is reduced. You can In Example 1 and Example 2,
Although the example using the GaAs substrate 1 has been described, the present invention can be easily applied to substrates made of other materials.

[0011]

FIG. 5 is a schematic diagram showing a band diagram and a refractive index distribution of a conventional GRIN-SCH semiconductor laser device. In the structure of FIG. 5, the optical confinement structure is InGaAs / GaAs SCH active layer and InG.
This is effectively done by an InGaAsP GRIN layer which is inserted between the aP cladding layer and the aP cladding layer and whose refractive index changes continuously.
In the In _x Ga _1-x As _y P _1-y GRIN layer, it is necessary to continuously change the forbidden band width and the refractive index and, at the same time, usually satisfy the lattice matching condition. Therefore, the semiconductor mixed crystal composition (x
And y) requires high precision control.

FIG. 6 is a schematic diagram showing a band diagram and a refractive index distribution of the semiconductor laser device of the present invention. It is a feature of the present invention that a superlattice in which GaAs quantum well layers (As series) and InGaP barrier layers (P series) are alternately stacked is used instead of the conventional GRIN layer.

Conventional In _x Ga _1-x As _y P _1-y GRI
Since the N layer has arsenic and phosphorus as the group V elements, and the vapor pressure of the group V is higher than that of the group III, accurate control of the composition is relatively difficult. On the other hand, it is easy to control the composition of the III-V mixed crystal semiconductor composed of one kind of V group element such as the superlattice in the present invention. Therefore, the use of these materials for the quantum well layer and the barrier layer forming the superlattice greatly contributes to the improvement of the fabrication controllability. On the other hand, the equivalent refractive index of the superlattice can be controlled by the layer thicknesses of the quantum well layer and the barrier layer. By continuously changing the thickness of each layer, it is possible to realize the equivalent of the GRIN region. Recent crystal growth technology (MBE, MO
With the progress of VPE, etc., the control of the layer thickness has become possible at the atomic layer unit level, which is far easier than the control of the semiconductor mixed crystal composition in the conventional GRIN layer.

Furthermore, when the group V constituent elements of the two types of materials that form the superlattice are different, their physical and chemical properties are also different, so that the two types of materials can be selectively etched. By utilizing this property, it is easy to perform fine processing such as stopping etching or forming a diffraction grating near the superlattice. Thus, according to the present invention, III containing arsenic and phosphorus as group V constituent elements
It is possible to realize a GRIN region using a group-V mixed crystal semiconductor or the same as a superlattice layer without difficult composition control. Further, it is easy to apply to fine processing by using selective etching.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a first exemplary embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view showing details of the configuration near the active layer in the first embodiment shown in FIG.

FIG. 3 is a perspective view including a cross section taken along the line AA ′ showing the configuration of the second exemplary embodiment of the present invention.

FIG. 4 is an enlarged cross-sectional view showing details of the configuration near the active layer in the second embodiment shown in FIG.

FIG. 5 is a band diagram (a) and a refractive index change diagram (b) in the vicinity of an active layer of a conventional semiconductor laser.

FIG. 6 is a band diagram (a) and a refractive index change diagram (b) in the vicinity of the active layer of the semiconductor laser of the present invention.

[Description of Reference Signs] 1 n-type GaAs substrate 2 n-type InGaP cladding layer 3a n-type GaAs quantum well layer 3b n-type InGaP barrier layer 4 n-type GaAs / InGaP superlattice layer 5a InGaAs quantum well active layer 5b GaAs barrier layer 6 InGaAs / GaAs active layer 7a p-type GaAs quantum well layer 7b p-type InGaP barrier layer 8 p-type GaAs / InGaP superlattice layer 9 p-type InGaP clad layer 10 p-type GaAs cap layer 11 semi-insulating InGaP layer 20,30 portion 101,102 electrode

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[Procedure amendment]

[Submission date] November 8, 1993

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 4

[Correction method] Change

[Correction content]

[Figure 4]

Claims (3)

[Claims] 1. A superlattice layer in which a plurality of quantum well layers and barrier layers having a forbidden band width larger than the quantum well layers are alternately laminated on at least one side in the laminating direction of the active layer for emitting light. In the semiconductor laser described above, the quantum well layer of the superlattice layer contains only arsenic as a group V constituent element.
A semiconductor laser using a superlattice layer, which is formed of a group V mixed crystal semiconductor and in which the barrier layer of the superlattice is formed of a group III-V mixed crystal semiconductor containing only phosphorus as a group V constituent element. element. 2. The quantum well layer of the superlattice layer is GaAs
2. The semiconductor laser device using a superlattice layer according to claim 1, wherein the barrier layer is InGaP. 3. The superlattice layer according to claim 1, wherein the layer thickness of at least one of the quantum well layer and the barrier layer of the superlattice layer is gradually increased or decreased. Used semiconductor laser device.