JPS6046087A - Distributed bragg reflection type semiconductor laser - Google Patents

Abstract

PURPOSE:To improve the reproducibility of element characteristics and the yield of manufacturing an element by forming a photoguide layer in series with an active layer to be photorecombined, thereby forming a diffraction grating on a semiconductor substrate having a flat surface. CONSTITUTION:A diffraction grating 2 is formed on an N type InP substrate 1, a P type InGaAsP photoguide layer 3 and an N type InP layer 4 are laminated, a photoguide mesa 5 and a mesa 6 of an active region are formed by etching, and a buried crystal growth is performed. A P type InP clad layer 9 is laminated except the top of the mesa 5, an N type InP current block layer 10 is laminated except the mesa 5 and the mesa 6 of the active region, and a P type InP buried layer 11 and a P type InGaAsP electrode layer 12 are laminated over the entire surface so that an N type InP buffer layer 7 is laminated except the top of the mesa 5 and a non-doped InGaAsP active layer 8 is independently formed on the upper surface of the mesa 6 of the active region. Then, electrodes are formed, and a distributed Bragg reflection type semiconductor laser of buried hetero structure is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a buried heterostructure semiconductor laser in which an active layer is surrounded by a semiconductor layer having a larger energy gap and a lower refractive index than the active layer, in particular a light guide layer having a diffraction grating. The present invention relates to a distributed Bragg reflection semiconductor laser in which a distributed Bragg reflection type semiconductor laser is formed.

Buried heterostructure semiconductor lasers (BH-LDs) have excellent characteristics such as low oscillation threshold current and high temperature operation, and are attracting attention as light sources for optical fiber communications. By the way, in a normal BH-LD, when high-speed modulation is performed, the wavelength is no longer single, and the effects of optical fiber material 1 dispersion, etc.
This greatly limits the transmission band. In contrast, distributed feedback semiconductor lasers (DFB-LD) and distributed Bragg reflection semiconductor lasers (DBI (- LD).

All of these semiconductor lasers have a diffraction grating with an appropriate pitch, and semiconductor lasers with such a structure have recently been developed, and they oscillate at a single wavelength even when modulated at high speeds of several hundred megabytes and 28 microseconds. The result is as follows. As an example, as reported by Mr. Abe et al. in Electronics Letters, Vol. 18, No. 10, pp. 410 to 411, published in 1982, there is a direct coupling type of embedded structure. Distributed Bragg reflection semiconductor laser (BH-BJB-DBR-LD
) and obtained single-axis mode oscillation. This semiconductor laser combines a buried active layer ζ and a series ζζ optical guide layer,
A diffraction grating is formed on the light guide layer.

This semiconductor laser requires three liquid phase growth steps, and the manufacturing process is outlined as follows. First of all, n-In
n-Ink, InGaAsP active layer, InG on P substrate
A normal DH structure wafer is fabricated by laminating an aAsP meltback prevention layer, a p-InP cladding layer, and a p-InGaAsF electrode layer using the As method.

Next, a 5i02 mask with a width of about 400 μm is formed parallel to the <di/X> direction of the InP, and the p-InP cladding layer is selectively etched away. In the second liquid phase growth step, an InGaAsP optical guide layer and an InP layer are laminated only on the previously etched portion.

At this time, the meltback prevention layer and the active layer protruding from the etched surface melt back immediately before or during the growth of the light guide layer, and the original guide layer becomes n -'I.
It is located on the n-P layer at approximately the same height as the active layer. Go down like that. Next, in order to obtain a buried structure, mesa etching was performed deeper than the active layer in parallel to the (OV I ) direction to form a mesa stripe, and then in the third liquid phase growth process, two layers of p-InP and n-InP were formed. Laminate two current blocking layers.Finally, 0.25μ is applied only to the light guide layer.
A diffraction grating with a pitch of m is formed and electrodes are formed to obtain a desired semiconductor laser. In the I) BR-LD fabricated in this way, Mr. Abe et al. obtained a device with an OW oscillation threshold current of 138 mA at 0°C, an external differential quantum efficiency of 11%, and stable single-axis mode oscillation up to 22°C. Ta. This device has no mode skipping over the temperature range ζ from 200 K to 260 K, and the temperature change rate of its oscillation wavelength is Q,
It was ttA/°C.

By the way, in the above-mentioned semiconductor laser, when forming the diffraction grating on the original guide layer, the stripes of the optical guide layer with a width of about 3 μm are covered with a single layer of buried semiconductor of InP, and photoresist is first applied to the uneven portions. Then, laser interference exposure is performed. If a photoresist is applied to an area where the InP buried layer is higher than the optical guide layer, the photoresist will become thicker in that area, making it difficult to successfully fabricate a diffraction grating.

Therefore, the buried InP layer is selectively etched little by little, and the laser interference exposure is performed after the height of the buried InP layer becomes approximately the same as the height of the light guide layer.

One major drawback is that the liquid phase growth process must be performed three times, the manufacturing process is complicated, and the yield of device manufacturing is low.

In other words, the three liquid phase growth steps and the complexity of fabricating the diffraction grating are major bottlenecks, and it is possible to reduce the number of liquid phase growth steps and at the same time form a diffraction grating on a uniform surface. can reduce the above-mentioned problems to a considerable extent.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above drawbacks and provide a buried heterostructure distributed Bragg reflection type semiconductor laser in which the reproducibility of characteristics and the yield of the device manufacturing process are significantly improved.

The structure of the distributed Bragg reflection type semiconductor laser according to the present invention includes at least an active layer on a semiconductor substrate, an energy gap larger than that of the active layer, and a period of n on one surface.
- In a distributed Bragg reflection type semiconductor laser having an optical guide layer in which a diffraction grating of λ/2 (where n is an integer and λ is an oscillation wavelength in the active layer) is formed, the active layer that emits light and recombines is a mesa. It is characterized in that it is formed on the upper surface of the stripe, and the active layer and the optical guide layer are directly coupled in a direction parallel to the laser resonance axis.

The present invention will be explained in more detail below using drawings showing embodiments.

FIG. 1 shows a buried heterostructure distributed Bragg reflection semiconductor laser (B HD, B R-LD) according to the present invention.
FIG. 3 is a perspective view showing the manufacturing process of one embodiment of the invention. To obtain such an H-DBR-LD, first, as shown in FIG. p
In0,7 @ GaO,22As648 p042
The optical guide layer 3 has a thickness of 0.4 μm, n-I n P
Layer 4 is laminated to a thickness of 1 μm. The diffraction grating 2 is formed on an n-InP substrate 1 having a (100) plane orientation and is repeated in the <ρ//> crystal direction. A diffraction grating with a period of 39ooX and a depth of 1500A was formed by ordinary laser interferometry using a He-Od gas laser. Etching was carried out using a photolithography method and an HBr-based mixed etching solution. pxno-78 to prevent the disappearance of the diffraction grating 2 due to high temperature maintenance, meltback, etc. during liquid phase growth.
Gaoat ASO411Po,112 light guide layer 3 was grown at a low temperature of around 600°C. In particular, in order to prevent meltback, a supercooling solution with a supersaturation degree of about 10° C. was used for growth. The semiconductor heterostructure wafer ζ produced in this way is shown in Fig. 1 (b).
) Etching is performed to form a mesa stripe shape as shown in FIG. 1, to form a light guide mesa 5 and an active region mesa 6.

When performing this kind of etching, first
An etching mask with a width of 3 .mu.m is formed in a horizontal plane to form mesa stripes with a depth of 4 .mu.m.

For etching, a mixed etching solution containing hydrochloric acid and acetic acid is used.
Utilizing the phenomenon of side etching, the mesa top was scraped so that the width was approximately O%T, that is, it had a triangular shape.

Even if it becomes trapezoidal instead of triangular, the width of the mesa top is 1
As long as it is sufficiently narrow, less than μm, it is sufficient. At this time, etching was performed so that the width of the diffraction grating 2 was approximately 1.5 μm. Only the part that becomes mesa 6 in the active Z region n -I n P M4, pT-no, 78
Gao, HAso, apO052 original guide layer 3 is selectively etched. These two semiconductor layers have a triangular shape with a height of 1.4 μm% and a Z side of about 1.5 μm, and when these are selectively etched, other portions are hardly etched. In the semiconductor wafer on which the optical guide mesa 5 and the active region mesa 6 have been formed by etching as described above, embedded crystal growth is performed. First, the n-I n P buffer layer 7 is formed except for the upper part of the optical guide mesa 5, and the emission wavelength is set to 1. : Non-doped I n9.72 Gao, 2s-Ago, 61 equivalent to 3 μm
The PO-49 active layer 8 is isolated on the top surface of the mesa 6 in the active region, and then the p-InP cladding layer 9 is placed on the top surface of the mesa 5 in the active region, and the n-InP current blocking layer 10 is placed so that the light guide mesa 5 and Except for the mesa 6 part of the active area,
Furthermore, p-InP buried layer 11, emission wavelength 1.2 μm
Equivalent p 1n0-78-GaO,,AsO・,6P
O. The electrode layer 12 is sequentially laminated in 7L layers over the entire surface. An n-I n P buffer layer 7 is formed on the upper surface of the mesa 6 in the active region by using a super cooling method with a thickness of 0.1 μm.
No-7! Gao, ASo, @I Po, 411
The active layer 8 was grown by a two-phase solution method, and was also laminated to a thickness of 0.1 μm on the upper surface of the mesa 6 in the active region.

At this time, a normal liquidus temperature is adopted, and the diffraction grating 2 on the mesa 6 disappears. Similarly, the p-InP cladding layer 9 was grown using the super cooling method, and the n-InP current blocking layer 10 was grown using the two-phase solution method. The semiconductor wafer subjected to mesa etching and buried growth as described above is subjected to electrode formation and cutting into individual laser pellets to obtain the desired BH-DBR-LD (Fig. 1 (C)). A cross-sectional view of the device at a portion 5 is shown in FIG.

In the part of light guide mesa 5, from the upper surface of the shrimp growth layer, pp.
-n -p -n (substrate) structure, and at the same time in other parts p-p-n-p non-doped active layer -n,
-n structure, and even if a negative bias voltage is applied to the growth layer side and the f1 substrate side, almost no current flows. On the other hand, in the active region part, the current flows only in the buried active layer part, so the leakage current in the BH-LD can be effectively
This can be suppressed.

Produced as above, T: InGaAs P/I
n PBH-DBR-LD, the length of the active region and the length of the optical guide layer are both cut to about 300 μm, the oscillation threshold current is 50 mA at room temperature CW, the differential quantum efficiency is 16%, and the temperature from 0°C to 50°C is A device that is stable and exhibits BR mode oscillation in the temperature range of

The temperature change rate of the oscillation wavelength in its operating temperature range is 0.9A/
It showed stable single-axis mode oscillation even during high-speed pulse modulation of 500 Mb/s. BH according to embodiments of the invention
-DBR-LDi In this case, the diffraction grating 2 is n -I n
It could be formed on the flat surface of the P substrate 1, the liquid phase growth process was performed only twice, and leakage current flowing to areas other than the active layer could be suppressed to a sufficiently small level. From the above, BH-DBR has good reproducibility of device characteristics and improved manufacturing yield.
-LD was obtained.

In the embodiments of the present invention, InP is used as the substrate, and InP is used as the substrate.
Although we have shown an element with a wavelength of 1 μm using a GaAs P layer as an active layer and a light guide layer, the semiconductor material used is not limited thereto, and can be used to cover the wavelength range from the visible light region to the far infrared region. , InGaP, GaAj? A,s'S
There is no problem in using other semiconductor materials such as b. In addition, the light guide mesa 5G shows a structure in which the semiconductor layer is not stacked with the n-InP current blocking layer at 10 years old, but the p
Since it is only necessary to create a current blocking mechanism with a -n -p -n structure, the two semiconductor layers, the p-InP cladding layer 9 and the n-InP current blocking layer 10, are the former guide mesa 58.
It doesn't matter if it grows to cover you.

The feature of the present invention is that an active layer for light emission recombination is buried and grown on the upper surface of the mesa stripe, and a light guide layer for DBR is formed in series therewith.

This allows the diffraction grating to be formed on a semiconductor substrate with a flat surface and requires two liquid injections.

A high-performance H-DBR-LD could be produced in a long process. 7. Leakage current to BH-LD can be sufficiently reduced, and the reproducibility of device characteristics and yield of device manufacturing are excellent. =BT-1-DBR-LD could be obtained.

-LDO) The manufacturing process is shown in a perspective view from T1 onward, and FIG. 2 is a cross-sectional view of the element in the light guide region. In the figure, 1 is an n-I n P substrate, 2 is a diffraction grating, and 3 is a P-:[
no-780a, ), 22 Aso, 44 P layer, 12
Light guide layer, 4 is n-InP layer, 5 is light guide mesa, 6
7 is the mesa of the active region, and 7 is the n-I n P buffer layer S.
8 is I no 72oa, 28AS0.6I Po
, 311 fka layer, 9 is p -1n P cladding layer, 10 is n -I nP current blocking layer,
11LCp-I n'P buried layer, 12 p-I
n. ,,BGa,,,2As0411 Pa-a2N flow layer respectively.

Representative Patent Attorney Uchihara Day Gi 1 Diagram Granny 2ml

Claims (1)

[Claims] On the semiconductor substrate
- In a distributed Bragg reflection type semiconductor laser having an optical guide layer in which a diffraction grating of λ/2 (where n is an integer and λ is an oscillation wavelength in the active layer) is formed, the active layer that emits light and recombines is a mesa. 1. A distributed Bragg reflection type semiconductor laser formed on a stripe upper surface, wherein the active layer and the optical guide layer are directly coupled in a direction parallel to a laser resonance axis.