JPH01103894A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To enable a basic lateral oscillation of a laser device of this design with a low threshold current by a method wherein a trench is provided so as to make its base reach to at least the interface between an upper clad layer and an active layer both comprised in a multilayer thin film. CONSTITUTION:A forward voltage is impressed between both electrodes 6 and 7, consequently electrons and electron holes are made to be injected into an active layer respectively from an n-type clad layer 4 and a p-type clad layer 2 and a p-type region 8, and thus a laser oscillation is made to start by recombining electrons and electron holes. Carriers are injected from an upper and a lower electrodes 4 and 2, therefore the combination is made to take place efficiently independently of a stripe width. And, a stripe-like multiple quantum type active layer 3 is larger than the mixed crystallized AlGaAs in refractive index, and moreover a empty space with the refractive index of 1 is formed above the both sides of the active layer by means of a trench 9, so that laser rays are trapped in the active layer 3 W in width. In result, a basic mode oscillation is made to start by a low threshold current. And, as the trench 9 is built, current flowing through both electrodes 6 and 7 is all injected into the active layer 3, which helps the threshold current decrease.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a semiconductor laser device used as a light source for various electronic devices.

Conventional Technology When a semiconductor laser and an electronic circuit are integrated in a hybrid or monolithic manner, the surface of the semiconductor laser device is flat and the electrode is formed on one of its main surfaces, which enables high-speed integrated circuits. This is important from the viewpoint of high reliability, ease of connection between nine circuit elements, etc.

Figure 5 shows a conventional example of a laser device constructed from this point of view (see Proceedings of the Japan Society of Applied Physics Autumn 1986 Academic Conference Proceedings 27a-T-8, p. 155, Makiuchi et al. 1) -Basic structure-'').

This device consists of high-resistance AlG on a semi-insulating GaAs substrate 1.
aAs layer 2. Multi-quantum well type active layer 5° high resistance AlGa
After forming the As layer 6 and the GaAs contact layers 7 and 8, Zn and Si are respectively diffused to form the p-type region 3 and the n-type region.
After forming the mold region 4, the remaining n-type G
aAs contact layer 7 and p-type GaAs contact layer 8
It is constructed by forming an n-side electrode 9 and an n-side electrode 10 in ohmic contact thereon.

In this device, carriers are injected from the n-type region 3 and the n-type region 4 into the multiple quantum well type active layer 5 having a stripe width W and are recombined to cause laser oscillation. The laser light is effectively confined in the multi-quantum well type active layer 5 having a stripe width W. In the stacking direction, adjacent high-resistance AlGaAs
The forbidden band width of the cladding layer 2.6 is sufficiently larger than that of the active layer 5, and in the direction perpendicular to the stacking direction, the layer adjacent to the active layer is mixed from the quantum well structure due to the disordering of Zn and Si. This is because the leading waveguide with the stripe width W is formed. As a result, stripe width W=0.5μ
A laser that oscillates with high efficiency at a threshold current value of 30 mA has been obtained.

Problems to be Solved by the Invention However, it is extremely difficult to form optical waveguides with extremely narrow stripe widths with good reproducibility by diffusing Zn or Si, and the stripe width of optical waveguides is extremely difficult. It is practical that the width is wide to some extent.

On the other hand, when the stripe width is increased to W=1.5 μm or more, the threshold current value increases by more than twice, and the efficiency decreases by 1/3.
It is known that the value decreases below. This is considered to be because carriers are injected laterally from each diffusion layer into the quantum well type active layer. That is, it is thought that as the stripe width of the active layer becomes wider, the concentration distribution of electrons and holes becomes more pronounced within the stripe, and the recombination probability decreases.

The present invention aims to provide a semiconductor laser device in which the active layer has a wide stripe width and which oscillates in a fundamental transverse mode at a low threshold current value.

Means for Solving the Problems The semiconductor laser device of the present invention includes a semi-insulating substrate, an active layer formed on the substrate, and an active layer adjacent to both sides of the active layer. a first multilayer thin film in a stripe shape consisting of cladding layers having a large forbidden band width and different conductivity types; and a stripe-like trench disposed on at least one side of the first multilayer thin film. A second multilayer thin film of the same conductivity type as the lower cladding layer of the first multilayer thin film, one electrode provided on the surface of the first multilayer thin film, and one electrode provided on the surface of the second multilayer thin film. The trench has a depth that reaches at least the interface between the upper cladding layer and the active layer of the first multilayer thin film.

Operation In this semiconductor laser device, since the active layer is sandwiched between cladding layers of different conductivity types in the stacking direction, carriers are injected into the active layer from both cladding layers in the thickness direction, that is, in the vertical direction. As a result, even if the stripe width of the active layer increases, electrons and holes recombine efficiently.

Furthermore, since current confinement is achieved by the striped trenches, carrier injection efficiency into the active layer is high, and fundamental transverse mode oscillation is possible with a low threshold current value even in a relatively wide active layer.

Example-4 = Hereinafter, regarding a semiconductor laser device according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 is a sectional view of this embodiment.

In the figure, 1 is a semi-insulating substrate. 2 is an n-type cladding layer, 3 is an active layer with a multiple quantum well structure, 4 is an n-type cladding layer, and 5 is an n-type contact layer 5, which are laminated in sequence on one main surface of the substrate 1. . A striped trench 9 is formed from the surface of this laminate to the interface between the active layer 3 and the cladding layer 4. Reference numeral 8 denotes a p-type region, which is formed by selectively diffusing, for example, Zn into a portion of the stacked body other than the ridge portion sandwiched between the trenches 9. Reference numerals 6 and 7 denote electrodes, which are formed on the p-type head region 8 and the top surface of the ridge portion, respectively.

A method for manufacturing the semiconductor laser device configured as described above will be described below.

Zn-doped A 1o on one main surface of the semi-insulating substrate 1
, 5Ga (1,5As) are grown to a thickness of 1.0 μm to form an n-type cladding layer 2. On this p-type cladding layer 2, three non-doped GaAs layers with a thickness of 100A, which will serve as well layers, are formed. Non-doped A with a thickness of 200A as a barrier layer
A multi-quantum well type active layer 3 is formed by growing four layers of IO, 3G ao, and 7A s layers alternately. On this active layer 3, Se-doped AlO, 5Gao, sAs was applied at 1.0 μm.
The n-type cladding layer 4 is formed by growing it to a thickness of m. On this n-type cladding layer 4, 0.3
The n-type contact layer 5 is formed by growing it to a thickness of μm. The laminate consisting of these layers 2 to 5 is formed by one crystal growth using metal organic vapor phase epitaxy. Next, a layer with a thickness of 6000 mm is deposited on the n-type contact layer 5 by plasma CVD.
A Si3N4 film of A is formed, and two stripe-shaped windows each having a width of 15 μm are opened in parallel in order to diffuse Zn into it, and then Zn is diffused. Here, the width of the striped portion left between the two windows is assumed to be 5 μm. Zn diffusion is
This is performed until p-type region 8 reaches substrate 1. The multi-quantum well type active layer 3 in the region where Zn has been diffused is in a mixed crystal state of AlGaAs with an averaged composition due to disordered atomic arrangement of the superlattice structure, and between the P-type regions 8 The stripe width W of the sandwiched multi-quantum well type active layer 3 is about 2 μm. After diffusing Zn, the Si3N4 film is removed and electrodes 6.7 are formed by a known method. Note that one electrode 6 is T
i / A u, and the other electrode 7 is A u G
It consists of e N i / A u. Finally, the n-type contact layer 5 and the n-type cladding layer 4 are selectively removed by reactive ion etching to form striped trenches 9 that reach the interface between the n-type cladding layer 4 and the active layer 3. Then, the pn junction between the p-type region 8 directly below the electrode 6 and the n-type cladding layer 4 directly below the electrode 7 is removed. Here, the stripe width of the trenches 9 is 2 μm, and the width d of the rigid portion sandwiched between the trenches 9 is 2 μm.

The characteristics of the semiconductor laser device manufactured as described above will be explained.

When a forward voltage is applied between the picture electrodes 6 and 7, electrons are injected into the active layer 3 from the n-type cladding layer 4, and holes are injected from the n-type cladding layer 2 and the p-type region 8, and recombine. Laser oscillation occurs. In this way, since carriers are injected through the upper and lower cladding layers 4 and 2, recombination occurs efficiently regardless of the stripe width. Further, the striped multi-quantum well type active layer 3 has a refractive index higher than that of mixed crystal AlGaAs, and the upper portions of both sides thereof are trenches 9.
Since a space with a refractive index of 1 is formed, light is confined in the active layer 3 of the stripe @W. As a result, fundamental mode oscillation occurs at a low threshold current value. Further, since the trench 9 is formed, all of the current flowing through the picture electrodes 6 and 7 is injected into the active layer, which helps to reduce the threshold current value.

FIGS. 2 and 3 show typical optical output-injected current characteristics and intensity distribution of a far-field pattern, respectively.

As is clear from FIG. 2, the multi-quantum well type active layer 3
Even if the stripe width W is as wide as 2 μmN degrees, a threshold current value of 28 mA is obtained, which is approximately the same as that of the conventional semiconductor laser device described above. Furthermore, as can be seen from FIG. 3, fundamental transverse mode oscillation was obtained.

= 8 - FIG. 4 is a sectional view of another embodiment. In this example,
The bottom of the striped trench 9 reaches the n-type cladding layer 2. In this case, the bottom of the trench only needs to be in the n-type cladding layer 2, and the formation of the trench is easier than in the above embodiment shown in FIG.

Since the active layer 3 is sandwiched between the trenches with a space having a refractive index of 1, a striped leading wavepath is formed. Its characteristics were similar to those of the above examples.

As described above, according to this embodiment, the active layer 3 is sandwiched between the cladding layers 2 and 4 of different conductivity types, and the striped trench 9 is formed. Current flows through 4. Therefore, basic structure mode oscillation is performed at a low threshold current value. In addition, substrate 1
Since it is semi-insulating and the picture electrodes 6 and 7 are formed on one main surface of the substrate 1, it can be easily integrated with electronic circuit elements such as field effect transistors.

In addition, in this example, GaAs-based/A I Ga A
Although the laser device was constructed using an s-based material, the material is not limited to this as long as it can construct a semiconductor laser device, and the electrode material may also be AuGeN i/A.
It is not limited to u, Ti/Au. Further, the bottom of the trench 9 may be in the active layer 3 or at the interface between the active layer 3 and the lower cladding layer 4.

Effects of the Invention In the semiconductor laser device of the present invention, the active layer is sandwiched between cladding layers of different conductivity types, and striped trenches are formed, so that carriers are efficiently injected into the active layer through these cladding layers, resulting in low Fundamental transverse mode oscillation occurs at the threshold current value. Further, since the substrate is semi-insulating and the paired electrodes are formed on one main surface of the substrate, integration with electronic circuit elements such as field effect transistors can be easily performed.

[Brief explanation of the drawing]

FIG. 1 is a structural sectional view of a semiconductor laser device according to an embodiment of the present invention, and FIGS. 2 and 3 are typical optical output-injected current characteristics and far-field characteristics of a semiconductor laser device according to an embodiment of the present invention. FIG. 4 is a cross-sectional view of another embodiment of the present invention, and FIG. 5 is a structural cross-sectional view of a conventional semiconductor laser device. DESCRIPTION OF SYMBOLS 1... Semi-insulating substrate, 2... P-type cladding layer, 3... Active layer, 4... N-type cladding layer, 5.・N-type contact layer, 6, 7...
...electrode, 8.old...p-type region, 9...trench. Name of agent: Patent attorney Toshio Nakao, 1 person:
Zeyo intrusion sound

Claims (1)

[Claims] It consists of a semi-insulating substrate, an active layer formed on the substrate, and cladding layers adjacent on both sides of the active layer, which have a wider band gap than the active layer and have different conductivity types. a striped first multilayer thin film; and a striped first multilayer thin film having the same conductivity type as the lower cladding layer of the first multilayer thin film, which is disposed on at least one side of the first multilayer thin film via a striped trench. a second multilayer thin film, and one electrode provided on the surface of the first multilayer thin film;
the other electrode provided on the surface of the second multilayer thin film, and the trench has a depth that reaches the interface between at least the upper cladding layer of the first multilayer thin film and the active layer. A semiconductor laser device characterized by: