JPH0437184A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To provide a high power continuous oscillation semiconductor laser with good reproducibility by laminating on a semiconductor substrate a first cladding layer comprising III-V group compound semiconductor, an active layer, and a second cladding layer, and forming a first optical waveguide layer between the first cladding layer and the active layer, and further forming a second optical waveguide between the active layer and the second active layer. CONSTITUTION:There are formed on an n type GaAs substrate 11 a buffer layer 12, a lower cladding layer 13 comprising III-V group compound semiconductor, a lower optical waveguide layer 14, an active layer 15, an upper optical waveguide layer 16, and an upper cladding layer 17, and further a contact layer 18. After etching is done to an interface between the upper optical waveguide layer and the cladding layer, a rib is buried with ZnSe which ZnSe is then epitaxially grown to form single crystal ZnSe 20 on a portion where no rib is existent and polycrystalline ZnSe 21 on the rib. The polycrystalline ZnSe on the rib is completely removed and the upper surface of the rib and the upper surface of the single crystal ZnSe buried layer are flattened. After the removal of the polycrystalline ZnSe laminated on the rib the substrate is polished into a 20-1000mum thickness.

Description

[Detailed description of the invention] [Industrial application fields] Ru.

[Prior Art] It-VI group compound semiconductors such as zinc selenide (ZnSe) and zinc sulfide (ZnS), as well as their mixed crystals, have a wide bandgap, high specific resistance, and low refractive index. Taking advantage of these characteristics, for example, Zn5e thin films are used as current confinement layers and optical confinement layers in AlGaAs semiconductor laser devices. FIG. 4 is a cross-sectional view of the structure of a Zn5e-embedded Mi-type A, IGaAs semiconductor laser published by Iwano et al. in the Proceedings of the Japan Society of Applied Physics (Spring 1988, 28p-ZH-8). The semiconductor laser includes a cladding layer (13) having a refractive index larger than that of the active layer (41) on both sides of the active layer (41).
, 17), and is processed into a rib shape by etching halfway through the upper cladding Fa (13). This rib is Zn5
An optical waveguide is formed by embedding the e-layer (20), and at the same time, the ZnSe layer plays a role as a current confinement layer, and at the same time, by taking advantage of its low refractive index, there is a Creates an effective refractive index step in
It also plays a role as a light confinement layer. Compared to other materials used for confinement layers, Zn5e has the characteristics of high resistivity and low refractive index, and it effectively confines carriers and light waves within the optical waveguide, making it possible to improve the It is possible to easily realize threshold value and high efficiency.

[Problems to be Solved by the Invention] However, there is a limit to the ability to increase the output power of Zn5e embedded semiconductor lasers according to the prior art.For example, when used as a pickup light source for an optical disk system, it is difficult to increase the transfer rate expected in the future. is insufficient.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a high-power semiconductor laser that can continuously oscillate at a high output of 100 rnW or more with good reproducibility.

[Means for Solving the Problems] The semiconductor laser of the present invention has a rib-shaped optical waveguide made of a laminated structure of m-v group compound semiconductors, and the optical waveguide is embedded with a layer of II-Vl group compound semiconductors. In the semiconductor laser, the optical waveguide includes at least a first cladding layer, an active layer, a second cladding layer made of an m-v group compound semiconductor stacked on a semiconductor substrate, and the first cladding layer and the active layer. a first optical waveguide layer provided between the active layer and the second optical waveguide layer provided between the active layer and the second active layer, and the active layer has a film thickness of 20 to 1
00 people.

[Example] A first example of the high-power semiconductor laser of the present invention is shown in FIG.

An n-type lower cladding layer, an n-type lower optical waveguide layer, an active layer, a p-type upper optical waveguide layer, a p-type upper cladding layer, and a p-type contact layer are sequentially laminated on an n-type GaAs substrate. The contact layer and the upper cladding layer are processed into rib shapes. The optical waveguide formed of a ■-■ group compound semiconductor is embedded with Zn5e, which is a ■-■ group compound semiconductor. The active layer is made of non-doped aAs.
The film thickness is 50 people.

Here, the method for manufacturing a high-power semiconductor laser of the present invention will be described in a second manner.
This will be explained using figures.

On the n-type GaAs substrate (Step 1), an n-GaAs buffer layer (12), n-A 1 eAl! G a [1,
6 [IAS lower cladding layer (13), n - A 111
．． 311G a evsA s lower optical waveguide layer (14)
, non-doped GaAs active layer (15), I) A
111.311G ae, 711AS upper optical waveguide layer (16), p-A I [1, Jl] G a e.

A 6BAs upper cladding layer (17) and a p-GaAs) cladding layer (18) are epitaxially grown in sequence. Growth is performed by metal organic chemical vapor deposition using organic metals such as trimethyl gallium (TMG) and hydrides such as arsine as raw materials, and the film thickness of each layer is the lower cladding layer, lower optical waveguide layer, and active layer. , upper optical waveguide layer, upper cladding layer, 1.0 μm, 0.3 μm, 0.005 μm, 0.0 μm, respectively.
3μm! , 0 μm. Next, an insulating film (such as silicon dioxide (S i 02 )) is formed on the contact layer.
19) is deposited. 5102 deposition is performed using atmospheric pressure chemical vapor deposition, and the film thickness is 600 to 5000.
Figure 2(a)).

Thereafter, the insulating film is patterned by a photolithography process, and ribs are etched using the insulating film as a mask. A sulfuric acid-based etchant is used for etching the ribs, and etching is performed up to the boundary between the upper optical waveguide layer and the cladding layer (FIG. 2(b)).

After etching the ribs, the T-knob is embedded with Zn5e while the insulator mask remains on the ribs. The buried growth performed here is also performed by an organometallic chemical vapor deposition method using dimethylzinc dimethylselenium duct (DMZn-DMSe) and hydrogen selenide as raw materials, and the growth temperature is 275°C. When Zn5e is grown using Ebitashal growth, single-crystal Zn5e (20) grows in areas without ribs, and polycrystalline Zn5e (21) grows on the ribs because an insulating mask is formed (21). Figure 2 (C
)).

The polycrystalline Zn5e layered on the ribs is removed by reactive ion beam etching (RIBE). Polycrystalline Z
The etching rates of n5e, single crystal ZnS e, and 5i02 are the highest among polycrystalline ZnS e, 51
02 is the smallest. Therefore, by utilizing this difference in etching rate, the amount of etching was adjusted so that the polycrystalline Zn5e on the ribs was completely removed and the top surface of the ribs and the top surface of the single-crystal Zn5e buried layer were at the same height. Figure 2 (d)) to flatten the nof. Note that the etching rate of SiO2 is 1/3 to 1/3 that of Zn5e.
4, which is very small, prevents the risk of notching and etching the rib head.
It also plays a role as an etching stop layer.

After removing the polycrystalline Zn5e layered on the ribs, the insulating film of the mask is removed and the substrate is polished to a thickness of 100 μm. Finally, when the p-side and n-side electrodes are deposited, Zn5e
A buried type 5CH-SQW laser is completed (Fig. 2(e)).

When the current-optical output (1-L) characteristics of the semiconductor laser of the present invention were measured, in the case of a non-coated element, the threshold current value was 10 mA, kink-free up to 70 mW, and the COD level was 85 mW. This is because the active layer is a single quantum well (SC) 1) with a film thickness of 50 nm, and the edge fracture density, which is the biggest factor determining the maximum output of a semiconductor laser, is different from that of a normal double hetero This is due to the dramatic improvement compared to junction semiconductor lasers. In other words, the edge fracture density of a normal double heterojunction semiconductor laser is approximately 2 MW.
/cm2, whereas that of the semiconductor laser of the present invention incorporating the SQW structure is approximately 6 MW/cm2, which is three times the value of the double heterojunction semiconductor laser. Furthermore, by making the active layer thinner, light seeps into the optical waveguide layer more, which also contributes to improving the maximum output of the semiconductor laser. In fact, in a semiconductor laser in which the thickness of the optical waveguide layer is increased from 0.3 μm to 0.5 μm and the effective refractive index of the active layer is decreased, light leaks out of the active layer and its maximum output is reduced. The non-foot device output was 103 mW.

By the way, in a single quantum well structure in which the active layer is not a single layer of semiconductor, but an ultra-thin film layer sandwiched between upper and lower semiconductor layers with a larger forbidden band width than the ultra-thin film layer, the electrons in the ultra-thin film layer are dispersed in a discrete manner. It has energy, and by changing the thickness of the ultra-thin semiconductor layer that makes up the active layer, the oscillation wavelength of the semiconductor laser can be changed.

The Zn5e used as the buried waste has a higher resistivity than the ■-■ group compound semiconductor, and carrier confinement works effectively. Furthermore, since the refractive index is approximately 2°54, which is smaller than that of GaAs, etc., light waves are effectively confined in the lateral direction. Due to this carrier and light wave confinement effect, a lower threshold value and higher efficiency can be easily achieved.

Furthermore, Zn5e has excellent thermal conductivity compared to other dielectric insulating films such as SiO2. Therefore, when used for current confinement, the generated heat is efficiently dissipated even if continuous driving at high output is required, minimizing the reduction in efficiency due to the rise in chip temperature or the increase in the threshold current value. can be suppressed to

A second embodiment of the invention is shown in FIG. The difference from the first embodiment shown in FIG. 1 is that the optical waveguide structure is etched into a rib shape until it reaches the substrate, and that the ribs are filled with Zn5I1 that lattice-matches with GaAS.
．． These are the two points made by e6Ses9A (31).

In this example, Z whose lattice constant matches that of the active layer is
Because the ribs are filled with nSSe mixed crystal, the stress on the active layer due to lattice mismatch is reduced.Therefore, lattice defects are less likely to occur in the active layer, resulting in high reliability of the semiconductor laser. Also, from the side of the ZnSSe that forms the buried layer, no stress is applied at the interface with the rib side surface during the buried growth, making it possible to form a high-quality buried layer. , the adhesion to the side surfaces of the ribs is improved, and the effect of confining light waves and carriers is further improved.

In the description of the embodiments of the semiconductor laser of the present invention, Zn, which is a ■-■ group compound semiconductor, is used as the buried layer.
Although the case where S es or ZnSSe is used has been described, similar effects can be obtained even when other ■-■ group compound semiconductors are used as the buried layer. In other words, group III raw materials include selenium, sulfur,
Tellurium, etc. can be used, and zinc, cadmium, etc. can be used as Group II raw materials, and good characteristics can also be obtained in binary, ternary, quaternary, etc. mixed crystals that combine these. . In any case, it goes without saying that better results can be obtained by lattice matching the Ⅰ-V group compound semiconductor forming the active layer and the buried layer.

In addition, the semiconductor laser of the present invention can be similarly applied to laser materials other than AlGaAs-based materials, such as rnGaAsP-based and InGaP-based materials.

Furthermore, similar effects can be expected for a structure in which the conductivity types of each layer are all reversed (a structure in which p is replaced with n and n is replaced with p) in the example.

[Effects of the Invention] The semiconductor laser of the present invention has the effects described below, and at the same time makes it possible to make full use of the characteristics of n-vx compound semiconductors and to manufacture a semiconductor laser that continuously oscillates at a high output of nearly 100 mW. shall be.

(1) Since the lattice constant of the II-VI group compound semiconductor in which the optical waveguide is embedded is close to that of GaAs, stress on the active region due to lattice mismatch can be minimized, resulting in a long life of the semiconductor laser and Improved reliability at high output can be measured.

(2) Since the n-VI group compound semiconductor has a high resistivity and a low refractive index, carriers and light waves are effectively confined within the optical waveguide. As a result, lower threshold voltage and higher efficiency of the semiconductor laser can be easily achieved.

(3) Furthermore, II-VI group compound semiconductors have much higher thermal conductivity than dielectric thin films. Therefore, even when continuous oscillation is performed at high output, the generated heat is smoothly dissipated from the chip, which reduces the possibility of a decrease in efficiency or an increase in the threshold value due to a rise in the temperature of the chip.

In addition to the effects of burying the ribs with the ■-■ group compound semiconductor described above, the following effects can also be obtained by introducing a quantum well structure into the active layer.

(4) By introducing a quantum well structure into the active layer, electrons in the active layer have discrete energy.

Therefore, by changing the thickness of the active layer, the oscillation wavelength of the semiconductor laser can be changed.

(5) By introducing the quantum well structure, the edge fracture density has been dramatically improved compared to a semiconductor laser having a normal double heterojunction. This means an increase in maximum output. In fact, in the semiconductor laser of the present invention, a high output of 103 mW was recorded with a non-coated element.

[Brief explanation of drawings]

FIG. 1 is a structural sectional view of a semiconductor laser showing a first embodiment of the present invention. FIGS. 2(a) to 2(e) are process cross-sectional views illustrating the manufacturing process of the semiconductor laser according to the first embodiment of the present invention. Figure 3 shows 7! of the present invention! FIG. 2 is a structural cross-sectional view of a semiconductor laser showing an example of Z2. FIG. 4 is a structural sectional view of a semiconductor laser showing a conventional example. 11 - n-type GaAs substrate 12... n-type GaAs buffer layer 13- n-type AI 1! , JTIG a [], 61
]A S cladding layer 14- n '42 A f [!
, 3 [IG a [1, 7 [IA S optical waveguide layer 15.
...Quantum well active layer 16-p type Al 11.311G a 57sA s
Optical waveguide layer 17 --- p-type Al e4oGa 8
．． aeA scla 11 layer 18...p-type GaAs contact layer 19...5j02 mask 20...single crystal Zn5e 21...polycrystalline Zn5e 22...p-type ohmic electrode 23...n-type ohmic, Electrode 31--Single crystal ZnSSe 1--Active layer (a> (b) (c)

Claims (1)

[Claims] In a semiconductor laser having a rib-shaped optical waveguide made of a laminated structure of III-V group compound semiconductors, and in which the optical waveguide is embedded with a II-VI group compound semiconductor layer, the optical waveguide is laminated at least on a semiconductor substrate. a first cladding layer, an active layer, a second cladding layer made of a III-V group compound semiconductor, and a first optical waveguide layer provided between the first cladding layer and the active layer, an active layer and 1. A semiconductor laser comprising a second optical waveguide layer provided between second active layers, the active layer having a thickness of 20 to 100 Å.