JPS5972787A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To facilitate the formation of a non-injection region at the stage of crystal growth and to improve the reproducibility of characteristics of DFB-LD and the yield rate in manufacture, by the constitution wherein a mesa stripe, which includes an active layer of BH-LD that undergoes light emitting recombination, has a semiconductor layer having a partially different conductive type on the active layer. CONSTITUTION:A diffraction grating 2 is formed on an N-InP substrate 1. An N-In0.85 Ga0.15As0.33P0.61 current blocking layer 7, which corresponds to a light emitting wave length 1.1mum, is sequentially laminated to a thickness of 0.2mum. Thus a DH wafer is obtained. A photoresist mask is formed on this wafer. The N-In0.85Ga0.15As0.33P0.67 current blocking layer 5 is partially etched away. After the etching, the remaining part of the N-In0.85Ga0.15As0.33P0.67 current blocking layer 7 is made to be a non-injection region. Thereafter, a mesa stripe 10, which includes an active layer that undergoes light emitting recombination in the direction of <011> in parallel, is formed. Two parallel etching grooves 8 and 9, which hold the strip in between, are formed. Since the non- injection region can be readily formed at the stage of the crystal growth in this way, the reproducibility of the characteristics of DFB-BH LD, the yield rate in manufacture, and reliability can be improved to the large extent.

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. The present invention relates to a distributed feedback buried semiconductor laser having a carrier injection region.

Buried heterostructure semiconductor lasers (BH-LDs) have excellent characteristics such as low oscillation threshold current, stabilized oscillation transverse mode, high optical output operation, and high temperature operation, and are suitable for optical fiber communication. It is attracting attention as a light source. By the way, in a normal BH-LD, when modulated at high speed, the wavelength is not single, and even when used with direct current, the wavelength jumps discontinuously due to temperature rise or change in injection current. When a BH-LD is modulated at high speed and the laser light is input to one end of an optical fiber, the waveform of the light emitted from the output end of the optical fiber is distorted due to material dispersion of the optical fiber.

In contrast, high-speed modulation at several hundred megabits/second is used to
A distributed feedback semiconductor laser (DFB), which has a diffraction grating with a certain appropriate pitch, is used as a semiconductor laser that exhibits an oscillation wavelength of
-LD) has been proposed. Normal B) (-LD has a Fabry-Perot resonator structure, and the light confined in the active layer is caused to resonate and oscillate using the cavity mirror surfaces at both ends of the LD chip, whereas DFB- L
In D, a diffraction grating is provided near the active layer, and light waves reciprocate within the diffraction grating and resonate. Recently, various semiconductor lasers having a structure combining FB-LD and BH-LD have been developed, and results have been obtained that oscillate at a single wavelength even when high-speed pulse modulation is performed at 500 Mbit/sec. However, in DFB-LD, if a laser resonator surface is formed due to cleavage when cutting individual laser pellets from a laser wafer,
Single-axis mode oscillation cannot be obtained using a diffraction grating. In other words, it is important to suppress the Fapry-Perot mode. Conventionally, to prevent this, one end face was etched diagonally,
Alternatively, the final electrode layer may be made of n-type and p-type impurities are partially diffused, or SiOs, S
A method has been used in which an insulating film is formed, and only a part of the insulating film is formed to form an electrode. Broadly speaking, there are two methods: one is to make one laser end face oblique, and the other is to make a part of the laser stripe into a non-emitting region by cleaving the laser end face to reveal a crystal plane.
Various methods were used. However, in the former case, for example, even if a mixed etching solution such as Br-methanol is used, it is not always possible to obtain a completely oblique etched surface near the active layer. A disadvantage is that a very small portion forms a laser resonator with the crystal cleavage plane at the other end, resulting in a small axial mode standing near one central wavelength mode. In the latter case, small pinholes in the insulating film may cause an increase in reactive current that does not contribute to laser oscillation, leading to a rise in the laser oscillation threshold. If this is done, alloy spikes may occur at the edges of the insulating film, which may adversely affect the reliability of the device. Similarly, when impurities are partially diffused, problems such as pinholes existing in the insulating film arise, resulting in poor reproducibility and manufacturing yield. Therefore, if a non-implanted region is formed in advance at the stage of crystal growth, this problem will disappear.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, form a non-implanted region at the crystal growth stage, and significantly improve the reproducibility of characteristics and manufacturing yield of a distributed feedback type↓1! An object of the present invention is to provide an embedded semiconductor laser.

The structure of the buried structure semiconductor laser according to the present invention includes a multilayer structure semiconductor wafer in which a semiconductor multilayer film including at least a first conductivity type cladding layer, an active layer, and a second conductivity type semiconductor cladding layer is grown on a semiconductor substrate. In a buried heterostructure semiconductor laser formed by deep etching of the active layer to form a mesa stripe and then buried growth, the mesa stripe partially has a first conductive semiconductor layer in the laser resonance axis direction. A light guide layer and a diffraction grating having a pitch that is an integral multiple of 1/2 of the oscillation wavelength in the active layer are formed along the active layer.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated using drawing which shows an Example.

FIG. 1 is a plan view of a semiconductor group hetero (DH) wafer after methistrebe formation, that is, before buried growth, of DFB-BHLD5-, which is an embodiment of the present invention. Figure 2 shows the DFB-BHLD fabricated by performing overlay growth on the DH wafer shown in Figure 1.
FIG. 2 is a cross-sectional view of part A', that is, a cross-sectional view in the direction of the laser resonance axis including the mesa stripe part. Similarly, Figure 3(a)
3(b) is a sectional view taken along the line BB' in FIG. 1, and FIG. 3(b) is a sectional view taken along the line CC' of the fabricated DFB-BHLD.

The manufacturing process will be explained below mainly using the cross-sectional views of FIGS. 3fa) and 3(b). First, (100) n-InP substrate 1
For example, a diffraction grating 2 with a pitch of 0.23 μm is formed using a laser interferometry using a He-CD laser. This is <01
It is easy to understand that FIG. 2, which shows a sectional view in the direction of the laser resonance axis, is a cross-sectional view in the direction of the laser resonance axis. On the n-InP substrate 1 on which such a diffraction grating was formed, n1:no, as cao, which corresponds to an emission wavelength of 1.1#g, was formed.
ts As033Po, 67 light guide layer 3 with a thickness of 0.
Non-doped I corresponding to 3μm9 emission wavelength 1.55μm
n0.59 Ga6,41 A11O,90Po, 1C
The active layer 4 is made of pInO, 726-Ga02g Ago6t Po, which corresponds to the emission wavelength of 1.3 μm, and the thickness of the meltback prevention layer 5 is 0.15 μm, and the p-InP cladding layer 6 is 1 μm.

n InO, 85ca corresponding to emission wavelength 1.1μF#
o, ts As(1,33P0.61 current blocking layer 7
0.2 μm thick, sequentially laminated ABo, 33 Po, 6
7. The light guide layer 3 was formed using a super cooling solution with a supersaturation degree of △T=20°C.
59Gao4t All0.90 Po, 10 active layer 4
It is preferable to grow crystals using the overseeding method, which allows easy control of film thickness and good condition of the hetero interface. As shown in FIG. 1, the DH wafer obtained in this way has a
> direction, a photoresist mask is formed in parallel to the n-In0. B5 Ga0.15 All0.33
Po, 67 current blocking layer 7 is etched and removed. At this time, if a sulfuric acid-based mixed etching solution is used for etching, n-rno, ss cao, ts All0.33
Only the Po, 67 current block layer 7 is selectively etched, and the p-InP cladding layer 6 is not etched. After etching n-In0.85 GIlo, 15 A
The remaining portion of the 11O, 33Po, 67 current blocking layer 7 becomes a non-implanted region. After that, <0
11. Mesa stripe containing an active layer that emits light and recombines parallel to the direction 10. and two parallel etched grooves 8.9 sandwiching it. Mesa stripe 10 has a width of 2μ
m, etching $8, 9 is width 10gm, depth 3μm
Etching can be easily carried out using a Br-methanol mixed etching solution. After performing the above two etchings, as shown in Fig. 1, buried growth was performed on the H wafer, and the p-InP current current cross layer 2 layer 11 - InP current current cross layer 2 layer 12 was shifted only on the top surface of the mesa stripe. and then p-InP
Buried layer 13, P-In0 with emission wavelength equivalent to 1.3 μm
．． 72 GaO, 28 Aso, tit Po, 39 electrode layers 14 are laminated over the entire surface. Electrode formation is performed to obtain the desired DFB-BHLD. The mesa stripe 1° is partially n-I n 0.85 in the direction of the laser resonance axis.
Contains G B O, 15A80.33 Po, 67 current blocking layer. The mesa stripe itself has an npn structure in this part, and no current is injected into this part. As mentioned above, the mesa stripe 10 is partially a first conductivity type semiconductor layer n Ino, ss GILo, 15 A
11O, 33Po, 67% L flow book layer 7, and DI? The non-implanted region for suppressing the Fabry-Perot mode in 'B-BHLD could be easily formed at the crystal growth stage with an extremely high yield. In the DFB-BHLD manufactured in this way, the length of the implanted region is 4
00 μm, the length of the non-implanted region is 250 μm, the CW oscillation threshold current at room temperature is 5 (1 mA, and the temperature change in wavelength during CW oscillation is 0.8210°500 Mbit/'1f).
Even during high-speed modulation of lc, laser oscillation in one axial mode and DFB mode was obtained with good reproducibility.

InGaA in the 1,5 pm band, which is an embodiment of the present invention
In the aP/I rIPDB-BHLD, the mesa stripe itself partially included a non-implanted region in the direction of the laser resonance axis, and the Fabry-Bello mode in the DFB LD could be sufficiently suppressed. Such a non-implanted region can be easily formed during the crystal growth stage, and therefore the characteristics are more reproducible than in the conventional case.

Manufacturing yield and reliability have been significantly improved.

91 In the DFB-BHLD which is an embodiment of the present invention, the mesa stripe is partially formed of n-In0 in the direction of the laser resonance axis.
．． 85 cao, ts As (1, 33 Po, 67 current blocking layer 7 is formed and operates as a non-implanted region. In this way, the non-implanted region can be easily formed at the stage of crystal growth. , compared to the conventional example in which one end surface of the laser is etched obliquely, the DFB-
The characteristic reproducibility, manufacturing yield, and reliability of BHLD have been significantly improved.

In the embodiment of the present invention, InP is used as the substrate and I
Although we have shown an optical device with an oscillation wavelength of 1 μm using nGaAgP as the active layer and optical guide layer, it is not limited to this material system, and other materials may be used to cover the range from the visible light region to the far infrared region. There is no problem even if it is a semiconductor material. Moreover, DFB-BHLD which is an example
The diffraction grating used for the laser oscillation light of 1455 μm has a pitch of 0.23 μm;
A diffraction grating having a pitch of 10 - an integral multiple of /2 may be used. Furthermore, BH-L
In the example, a structure related to the transverse mode control of D was used, in which a mesa stripe was sandwiched between two etching grooves, but the present invention is of course not limited to this. This includes all BH-LDs whose layers are covered with other semiconductor materials.

The feature of the present invention is that in DF'B-BHLD, BH-LD
The mesa stripe including the active layer that undergoes light emission recombination has semiconductor layers of partially different conductivity types on the active layer. A non-implanted region could be easily formed at the stage of crystal growth. Therefore, compared to the conventional method of etching the laser resonator end face obliquely or forming a non-implanted region using an insulating film or impurity diffusion, DFB-L
The reproducibility of the characteristics of D and the manufacturing yield were significantly improved.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, and FIG. 3 (al, (b)) relate to DFB-BHLD, which is an embodiment of the present invention.
Figure 1 is a plan view of the DH-wafer after etching grooves are formed, Figure 2 is a cross-sectional view taken along line A-A' in Figure 1, and Figure 3 (a).
3 is a cross-sectional view of the BB' section, and FIG. 3 is a cross-sectional view of the c-c' section.
0JS Ga0.15 AIo, 33 Po, 67 light guide layer, 4 is In059GIL0.41 All0.9
0 Po, 10 active layer-, 5 is pInO, 72 GaO,
28Aso, 61 Po, 39 Meltback prevention layer, 6
is p-InP cladding layer 1.7 is n-InO, 85ca
o, ts As(1,33Po, 67 current blocking layer,
8 and 9 are etched grooves, 1o is a mesa stripe, 11 is a p-InP current blocking layer, 12 is an n-InP current blocking layer, 13 is a p-InP buried layer %14 is a p-InP
ay2Gio, zs All0.61 Po, 39 electrode layers respectively. Representative Patent Attorney Shinsuke Uchihara 1 Figure 2 Figure 13 /4 7 / 1] Figure 3

Claims (1)

[Claims] at least a first conductivity type semiconductor cladding layer on the semiconductor substrate;
A buried heterostructure is formed by etching a semiconductor multilayer film including an active layer and a second conductive semiconductor cladding layer into a multilayer structure semiconductor wafer, etching it deeper than the active layer to form a mesa stripe, and then growing it in a buried manner. In the semiconductor laser, the mesa stripe partially has a first conductivity type semiconductor layer in the direction of the laser resonance axis, and along the active layer, a light guide layer and a layer of 1/1 of the oscillation wavelength in the active layer.
A semiconductor laser comprising a diffraction grating having a pitch that is an integral multiple of 2.