JPS59169191A - Single axis mode semiconductor laser - Google Patents

Abstract

PURPOSE:To enhance the productivity by isolating a light guide layer, a buffer layer and an active layer between above the terrace-shaped region and the other region, and butting and connecting one end face of the light guide layer above the terrace-shaped region and the one end face of the active layer except the part above the terrace-shaped region, thereby reducing the number of steps of epitaxially growing. CONSTITUTION:A diffraction grating 20 is formed on a (001) plane azimuth N type InP substrate 1 so that the pitch direction becomes (110) direction. It is etched in parallel with the direction of T10 direction perpendicular thereto, and formed in shape as shown in (b). Then, an epitaxial growth is executed. An N type InGaAsP light guide layer 5, an N type InP buffer layer 2, a non-doped InGaAsP active layer 3 are grown in the laminated shape cut in the course at both sides of the stepwise difference part 10. Subsequently, electrodes are formed, cleaved in parallel with (110), a resonator surface is formed as a chip, thereby obtaining a single axial mode semiconductor laser. As described above, since it can be formed by one epitaxial growing step, the productivity is advantageously excellent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a base-axis mode conductor sensor suitable for a light source for a fiber optic communication system.

Is the transmission loss of optical fiber at wavelengths of 1.3 μm and 1.5 μm?
Due to the ultra-low loss of 0.3 to θ and 5 dB/km or less, ultra-long distance transmission experiments with relay intervals of 1,100 km or more have begun to be carried out in various places. Such an ultra-long distance optical fiber communication system is expected to be applied to submarine communication systems, etc., where it is advantageous to lengthen the relay interval.

In addition to the transmission loss of nine fibers, chromatic dispersion also becomes a problem in ultra-long distance conical transmission.
Since co-located semiconductor lasers usually have multiple oscillation axis modes, repeater spacing or transmission capacity is limited by chromatic dispersion rather than transmission loss. Therefore, in order to realize a long-distance, high-speed optical fiber transmission communication system, a semiconductor laser capable of single-axis mode oscillation is required. Examples of such a semiconductor laser include a distributed reflection type semiconductor laser or a distributed feedback type semiconductor laser in which a diffraction grating having a periodic structure is built inside without using a Fabry-Bérot reciprocator. The author invented a distributed reflection type semiconductor laser having the structure shown in FIG. 1 in 178824/1982. The feature of this distributed reflection type semiconductor laser is that it has a shape in which the optical power layer 5 on which the diffraction grating 20 is formed and the active piI 3 are coupled in a butt-like manner by effectively utilizing the crystal orientation dependence of epitaxial growth. The condensation efficiency of the propagating light between the active layer 3 and the light guide layer 5 is as high as about 90%, and the buried heterostructure is used, so that the firing threshold is 20% at room temperature.
High performance can be obtained, such as a low differential efficiency of ~30 mA and a high differential efficiency of 30 to 50 degrees. However, if the manufacturing process of this distributed reflection semiconductor laser employs a buried heat treatment, a total of three long epitaxial growth layers fl! Requiring sand was a drawback in terms of productivity.

The present invention provides a rotary-rotation mode laser beam that can be manufactured by reducing the number of epitaxial growth steps by modifying the h+L value of the distributed reflection semiconductor laser.

The single-axis mode semiconductor laser of the present invention has a semiconductor substrate having a terrace V region at the bottom of which is a diffraction grating having a periodic structure of irregularities on the upper surface, an optical guide layer of the first conductivity type, a light guide layer of the first conductivity type;
At least four layers of a second conductivity type cladding layer are formed for the buffer layer and the active layer of the bh, and the light guide layer, the buffer layer, and the active layer are formed separately above the terraced region and other regions. and one end surface of the light guide layer above the terrace-like region and one end surface of the active layer other than above the terrace-like region are butted and connected.

Another single-axis mode semiconductor laser of the present invention has, in addition to the above structure, a striped active region sandwiched between two grooves and comprising at least a light guide layer, a buffer layer, and an active layer; The structure includes a buried layer formed to surround the.

Next, embodiments of the present invention will be described in detail using the drawings.

FIG. 2 is a diagram showing the manufacturing process of the first embodiment of the present invention. First, as shown in FIG. 2(a), a substrate is placed on an n-type InP substrate 1 with a K(001) plane orientation at a period of about 2200X and a depth of about 0.1μ.
The diffraction grating 20 of m is formed by an interference exposure method using a He-Cd laser and a photophosphorography method so that the pitch direction is the <110> direction.

Next, not perpendicular to this but parallel to the TIO> direction (3HC1+
Etching is carried out using a solution of 100 ml (HaPO4) to form the shape shown in Figure 2 (bl).
The surface 11 etched to a depth of μm is the diffraction grating 20.
Since the depth of the surface is micro/J'l, no traces of it can be seen, resulting in a perfect mirror surface. Next, epitaxial growth is performed.

The tS length depends on the usual liquid phase epitaxial growth method using a carbon slide boat.

FIG. 3(c) shows the multilayer structure after growth. First, n-type In
GaAgP optical guide layer 5 (carrier concentration 5×10″′α
, thickness 05 μm, composition 13 μm in terms of emission wavelength) and n-type InP buffer layer 2 (carrier concentration s x 16
'--1, thickness 1μ, n), non-doped InGaAsP
Active W13 (thickness 01μm, oscillation wavelength 1.55μm)
m composition) is grown in a fXM shape with interruptions on both sides of the stepped portion 10. The reason why such a growth shape can be obtained is also shown in the patent application No. 178824/1985, but
When the supersaturation degree of the growth solution is as low as a few degrees, <O'l'
The stacking speed on the stepped portion 10 parallel to the l> direction is (00
1) This is because the speed of stacking on the surface is extremely slow. However, if the degree of supersaturation of the growth solution is as high as 10 degrees or more, the growth layer will grow to almost uniformly cover the surface. P-type InP cladding layer 4 (carrier concentration lXl0
P-type InGaAsP cap layer 6 (carrier concentration, 5X10"w-", thickness 0.
7Bm (composition of 1.2 μm in terms of emission wavelength) is grown from such a highly supersaturated solution to cover the entire surface. Here, the light guide layer 5, buffer layer 3 and active layer 3 are
The heights on both sides of the 1° step are different. Considering the etched surface 11 as a reference, the light guide layer 5 laminated on the diffraction grating 2o is located at a height of 12 μm to 17 μm. In contrast, the active layer 3 above the etched surface 11 is located at a height of 1.5 μm to 16 μm. Therefore, the two are connected in a butt-to-edge manner. Even if the growth film thickness during epitaxial growth fluctuates by about 10% for each layer, the film thickness of the light guide Ia5 is 0.
．． Since it was as thick as 5 μm, the positions of the end faces of the active layer 3 and the optical guide layer 5 were not completely misaligned, and the reproducibility of the connection between the two was good.

After completing the fabrication of the semiconductor wafer, electrodes are formed, the valve is opened parallel to <110), a resonator surface is formed, and a chip is obtained, thereby obtaining a single-axis mode semiconductor laser having the structure shown in FIG. 840. A part of the insulating film 30 is removed and one side electrode 3 is removed.
2, Ti/Pt/Au is vapor-deposited to form a striped current injection region 31. The n-side electrode 33 has A
6.ru using u /G e /N i. Diffraction grating 2
The light guide layer 5 on top of the diffraction grating 20 converts the light incident on the light guide layer 5 out of the light emitted by the active layer 3 due to the injected current into a Bragg beam determined by the period of the diffraction grating 20. Wavelength 1.55μ
Since the light is diffracted and reflected at m and returned to the active layer 3, it becomes a distributed reflection region, and forms a laser resonator for the active layer 3 together with the mirror surface formed by opening the valve on one side. If the length of the optical guide layer 5 on the diffraction grating 20 is 500 μm or more, a bright reflectance of 30% or more can be obtained in this region for laser oscillation light.

In addition, the active layer 3 and the light guide layer 5 are connected in a butt-to-edge manner, and the light coupling efficiency between them is 90 inches or more, and the loss of light at the connection portion is small. Therefore, the length of the active layer 3 is 2
When the voltage was set at about 00 am, the oscillation threshold was about 200 mA at room temperature, and the differential quantum efficiency was good at about 20 cm on one side. The oscillation wavelength was 155 μm and a single axis mode.

As described above, it can be seen that the single-axis mode semiconductor laser of the first embodiment of the present invention shown in FIG. 3 can be formed in -times of epitaxial growth process, and therefore has an advantage of excellent productivity.

The characteristics of the single-axis mode semiconductor laser of the first embodiment can be further improved by adopting a buried structure. FIGS. 4(a) to (el) are diagrams showing the manufacturing process of a buried type single-axis mode semiconductor laser according to the second embodiment of the present invention. First, the manufacturing process is similar to that of the first embodiment. A multilayer film substrate shown in FIG. 4(a) is manufactured by this method.This has almost the same structure as the substrate shown in FIG. 2(C), except that there is no cap layer 6 and 7. The film thickness of the InP type cladding layer 4 is as thin as about 1 μm.As shown in FIG.
Two parallel i!s with a depth of about 3 μm! 1 #13 and 14 are formed, and a mesa stripe 12 including the active layer 3 with a width of about 2 μm is formed between these two grooves.-0 Filling growth is performed on the substrate in this state. The state after the buried growth is shown in FIG. 5(c). Square-shaped InP current blocking layer 7 (carrier concentration lXl0"crn-", thickness at flat part 0.5
μm), n-type InP current confinement layer 8 (carriers are allowed to grow and do not grow on the mesa stripe 12). thickness 1.5 μm) and/type I nGaAsP
cap) N6C'r Yaria concentration 5X10" crnl,
The film thickness at the flat portion is 0.7 μm) and is laminated to cover the entire surface.

The fabrication of the semiconductor wafer is thus completed, and Ntfa is formed to form a chip having the structure shown in FIG. There is no need to inject current into the active layer 3 above the diffraction grating 20 (because S +
An Ox insulating film 30 is provided to limit the current injection region. The two electrodes 32 and the n-side electrode 33 are made of the same materials as in the first embodiment shown in FIG. The resonator length is the first
The length is set to be approximately the same as that of the embodiment. 7 side electrode 32
When a bias voltage is applied with positive on the n-side electrode 33 and negative on the n-side electrode 33, a forward current of the n-junction flows in the active layer 3 in the mesa stripe 12, causing luminescent recombination, but the area outside the mesa stripe 12 Since it is an in7 n junction, current flows and it is difficult to operate. Therefore, the injected current is efficiently concentrated in the active layer 3 within the mesa stripe 12. Further, since the optical guide layer 5 having a diffraction grating on the lower surface connected to the active layer 3 is also located within the mesa stripe 12, it becomes a rectangular waveguide. Therefore, since the light rrl confinement is good, most of the light incident on the light guide layer 5 from the active layer 3 passes through the diffraction grating 2'0.
It is reflected back to the active layer 3' through distributed reflection. Therefore, the concentration effect of the current in the active layer 3 and the light guide F4 of the light
5 and the confinement effect of the active layer 3, the oscillation characteristics are significantly improved compared to the first embodiment. The oscillation threshold was about 20mA, and the differential quantum efficiency was high, with values of about 50% on both sides. The linearity between the injection current and the optical output was also good, and an optical output of 20 rr+W or more was obtained at room temperature.

The oscillation wavelength is 155 μm as in the first embodiment.
It was in single axis mode at n.

As described above, the single-axis mode semiconductor laser according to the second embodiment of the present invention has almost the same function as the conventional example shown in FIG. It can be seen that the 2-bitaxial growth process has the advantage of requiring only 2 steps compared to the conventional 3 steps, and is superior in productivity.

The present invention is not limited to the above two embodiments. As a semiconductor material, A1 or In on a GaAs substrate is used.
It is also possible to use GaAsP or the like.

Finally, to summarize the t\f characteristics of the present invention, it is possible to reduce the number of vitaxial growth steps and increase productivity compared to the conventional method.

[Brief explanation of the drawing]

Figure 1 is a perspective view of a conventional single-axis mode semiconductor laser.
A cross-sectional view showing the manufacturing process of the second embodiment, FIG. 3 Sakaki is a perspective view of the first embodiment, and FIGS.
FIG. 5 is a perspective view showing the manufacturing process of the second embodiment. In the figure, 1 is an n-type InP semiconductor substrate, 2 is an n-type InP buffer layer, 3 is an InGaAsP active layer, 4 is an l-type nP cladding layer, 5 is an n-type InGaAIIP optical guide layer, 6 is a 7-type InGaAsP cap layer , 7 is a 7-type InP current blocking layer, 8 is an n-type 1nP current confinement layer, and 9 is a ? Form I
nP buried layer, 10 is a stepped portion formed by etching, 11 is an etched surface, 12 is a mesa stripe, 13 and 14 are two parallel grooves, 20 is a diffraction grating, 30 is S
A tow insulating film, 31 a current injection region, 32 a metal lightning chair on the door side, and 33 a metal electric camellia on the n side. 17th (C) 2θ

Claims (1)

[Scope of Claims] 1. A semiconductor substrate having a terrace-shaped region on which a diffraction grating having a periodic structure of irregularities is formed, a first conductive type light guide layer, a first conductivity type buffer layer, active layer, second
at least 4r92 of a conductive type cladding layer is formed;
The light guide layer, the buffer layer, and the active layer are formed separately above the terrace-like region and in another region, and one end surface of the light guide layer above the terrace-like region and the terrace-like region are formed separately from each other. A single-axis mode semiconductor laser characterized in that one end surface of the active layer other than the upper region is butted and connected. 2. A light guide layer of a first conductivity type, a buffer layer of a first conductivity type, and an active layer double-stranded are formed on a columnar substrate having a terrace-like region in which a diffraction grating having a periodic structure of irregularities is formed on the upper surface. 2
It comprises at least four conductive cladding layers, of which the optical guide layer, the buffer layer and the active layer are formed above the terraced area and formed above the other areas. It has a structure in which one end surface of the Y guide layer above the terrace-like region is in contact with one end surface of the active layer in the region other than above the terrace-like region.
7. A drive-shaped active region sandwiched between two pots and comprising at least the light guide layer, the buffer layer, and the active layer;
This active area is a pile! What is claimed is: 1. A single-axis mode r-body laser, comprising: