JPS6135585A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To obtain a semiconductor laser device which operates stably in the longitudinal single mode even during the modulation, by providing variations in the refractive index in the direction of propagation of light in a region on or near an active layer to which a photoelectric field extends. CONSTITUTION:Diffraction gratings having different pattern dimensions and a constant period of about 2,300Angstrom are formed all over the surface of an N type InP substrate 1 by X-ray lithography using a metal pattern as a mask. A diffraction grating having a depth of 400Angstrom and a width which varies in a range from 300-1,500Angstrom is transferred by employing the RIE method. An N type InGaAsP light guide layer 2, an InGaAsP active layer 3, a P type InGaAsP buffer layer 4, a P type InP layer 5 and InGaAsP surface layer 6 are laminated. A P-side electrode 8 and an N-side electrode 9 are respectively deposited on the upper and lower surfaces by evaporation, and cleavage is effected to obtain a desired semiconductor laser device. In this device, an average refractive index near the center of the cavity is larger than those near both ends of the cavity. Therefore, an oscillation molde is selectively obtained at a wavelength which is shorter than the Bragg wavelength, and the laser device operates in a single mode.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a semiconductor laser device.

6 [Background of the Invention] An example of a longitudinal single mode semiconductor laser is a distributed feedback laser, whose cross-sectional view is shown in FIG. 1. In FIG. n-type formed 1. nP substrate 1
On top, an n-type InGaAsP guide layer 2° InGaAsP active M3, an InGaAsP buffer layer atP-type InP
A cladding layer 5yp-type InGaAsP surface layer 6 is sequentially laminated, and a p-side electrode 8 is provided on the upper surface of the p-type InGaAsP surface layer 6, and an n-side electrode 9 is provided on the back surface of the n-type InP substrate 1. The distributed feedback laser device implanted as described above has a drawback in that light having two different wavelengths centered around the Bragg wavelength tends to oscillate simultaneously. For this reason, Document 1 proposes a method of unifying the axial mode by providing a non-uniform effective refractive index distribution with a period longer than the period of the diffraction grating in the light propagation direction.

However, the conventional device satisfies the above effect by making the width of the active layer variable (for example, Document 2). In this case, it is necessary to precisely control the width of the active layer.
It was difficult to expect reproducibility in device fabrication. Further, as another method, a method of unifying the axial mode by shifting the phase of the diffraction grating by λ/4 near the center of the cavity has been proposed in References 3 and 4.

However, even in this case, the unification condition is destroyed depending on the phase relationship of the waves in the arm opening plane, so it is difficult to perform stable single mode operation, especially when there is return light from the outside. It was difficult.

In addition, the above-mentioned documents 1 to 4 are as follows.

1) Tada et al., 1983 Spring Proceedings of the Japan Society of Applied Physics 4a-
H-I P117゜2) Suzuki, Tada, Institute of Electrical Communication Research Materials 0QE3) Eda et al., 1984 Dentsu Conference Proceedings P4-38 (1984).

4) Uchiyama et al., 1981 Dentsu Convention Proceedings P4-67 (1981)
84).

[Purpose of the invention]

An object of the present invention is to obtain a semiconductor laser device that operates in a single-axis mode even during modulation.

[Summary of the Invention] The oscillation wavelength of a distributed feedback laser has a finite resonator length, so there are many oscillation modes centered around the Bragg wavelength, and the mode with the lowest threshold gain is is determined by selective oscillation. If there is no effective refractive index distribution in the axial direction, the threshold gains of the two modes sandwiching the Bragg wavelength are equal, making it difficult to achieve a single mode ratio.

On the other hand, by providing a refractive index distribution, a gain difference is created between the two modes, and a single mode is achieved.

[Embodiments of the invention]

Embodiments of the present invention will be described with reference to the drawings. FIG. 2 is a sectional view showing a first embodiment of a semiconductor laser device according to the present invention, and FIG. 3 is a sectional view showing a second embodiment. Second
The first embodiment shown in the figure changes the refractive index of the waveguide almost periodically over the cavity, and the optical guide Ji13 is arranged such that the average refractive index changes near the center of the cavity and on the end face side of the cavity. This is a structure obtained by manufacturing such that the crystal thickness changes almost periodically, and the width of the gap that makes the thickness different varies across the cavity. A resist is applied to the entire surface of the n-type InP substrate 1, and a pattern of constant periodicity with different batten dimensions is applied using the well-known linear writing method using an electron beam or an X-ray lithography method using a metal batten formed using electron beam writing as a mask. 2300
After forming the human diffraction grating, RIE (reacti
depth 400 using the ve ion etching) method.
A diffraction grating whose width varies in the range of 300 to 1,500 people is transferred onto the surface of an InP substrate 1.

Next, OMVPE (organo l1etalli
n-type InGAsP optical guide layer 2 (Te-doped, carrier density 2 x 10mm, average thickness 0.1-0.2
μm, 15-1.3 μm), InGaAgP active layer 3
(Undoped, thickness 0.1~0.27zm, λg~1.
5 μm) p-type InGaAsP buffer layer 4 (Zn doped, carrier density 1x10"am-", thickness O-1 ~
O-2p m + λg~x, sum) w p type I
nP layer 5 (Zn doped, carrier density ~ I x 10
"am-", thickness 2-4 μm).

InGaAsP p surface layer 6 (Zn doped, carrier density 3 x 10"am-", thickness 0.2-0.4
A p-side electrode 8 (Au/Cr) and an n-side ffl electrode (
Au/AuGeN1) was formed by vapor deposition and cleaved to obtain a desired semiconductor laser device. In the above semiconductor laser, the average refractive index near the center of the cavity is larger than that near both ends of the cavity, so the oscillation mode on the shorter wavelength side than the Bragg wavelength selectively oscillates, resulting in single mode operation. . Note that also in the above semiconductor laser device,
Forming an SiNx anti-reflection film with a thickness corresponding to λ/4 on at least the − cleavage plane or both cleavage planes is as follows:
This was effective from the viewpoint of preventing mixture of Fabri-Parot modes. Further, in the above embodiments, the period of the diffraction grating was set to a constant value, but this is not necessarily necessary, and it is also effective in a chirped gelating laser in which the period is variable in the cavity direction.

The second embodiment shown in FIG. 3 is an application of the concept of this patent to a surface-emitting laser.The light-emitting layer 13 serving as the cavity of monodistribution feedback is a layer 131 and a layer 132 with a lower refractive index than this. This is an L1-layer dry structure consisting of L1 layers, and the ratio of these layer thicknesses is made to vary in various parts of the cavity.
Q: I'm packing.

OMVPE (or Hano v
otallic vapor phaoe epitax
n-type InGaAsP layer 11 (Te
Doped, carrier density 2×101"C!l-", thickness 0
．． 2 ~ 0.3 μm, λg ~ 1.15 μm
), n-type InP layer 12. (Te doped.

Carrier density 2 x 101 layers 1m-”thickness 204m
), then the period is 234. While keeping n m constant, the n-type InP layer 131 (Te do, -, carrier density I x 10"as-") and n-type InGaAsP
Layer 132 (Te doped, carrier density I x 10"t
x bow composition λg ~ 1.5 μm), and after forming 50 to 400 Japanese calendars 13 with a thickness ratio of 1 to 1 in a range of 10 to 1 to 1 to 1, successively p-type I n P Layer 5 (Z
A laser crystal is obtained by laminating n-doped, carrier density 7 x 10"am-", thickness ~20 μm) and undoped InGaAsP layer 6 (thickness 0.2-0.3 μm9 composition λg ~1.3 μm). Next, a double film insulating layer of S13N4/SiO□ was formed on the p-side surface of the device by sputtering, and a diameter of 20 μm was formed for partial excitation.
A circular window is opened and Zn is diffused into this part. After that, an n(llffl pole (AuGo Ni/A
u), p-side Trf1m (A u /Cr ) was formed by vapor deposition, and a window of 100 μmφ was formed on the n-side to obtain a desired element. To form the window, use a resist mask having a circular window to remove the electrode layer using an etching solution containing Br or etching solution, and then etching the InP layer 9 using an etching solution containing CQ. Finally, 11 layers of windows were opened using an etching solution containing HeSO4 as a main component.

The obtained device performed stable single mode operation like the device shown in Example 1. Note that chirp gelating as described in Example 1 can also be used in combination with the above laser device. Furthermore, 131 mentioned in the example,
Each layer of 132 does not necessarily have to be a single layer film formed with the same composition, and at least /p of each layer is InGaAsP and InP or InG having a different composition.
A multilayer film formed of nAsP may also be used.

〔Effect of the invention〕

As described above, the semiconductor laser device according to the present invention has a refractive index change that is periodic in the light propagation direction but non-uniform on average in the range covered by the optical electric field in or near the active layer. As a result, a difference occurs in the threshold gain between the longer wavelength side and the shorter wavelength side of the Bragg wavelength, resulting in the selection of one oscillation mode, making it possible to obtain a semiconductor laser device that stably operates in a single longitudinal mode even during modulation. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional longitudinal single mode semiconductor laser device, FIG. 2 is a sectional view of a first embodiment of the semiconductor laser device of the present invention, and FIG. 3 is a sectional view of the second embodiment. FIG. 1-n-type InP substrate, 2-n-type InGaAsP light guide layer, 3-InGaAsP active W, 4-p-type 1nGaA
sP buffer layer, 5... p-type InP cladding layer, 6.
...InGaAsP surface layer, 7... Diffraction grating, 8...
・P side electrode, 9...n side electrode, 11-InGaAs
P layer, 12-I n P layer, 13... multilayer laminated part,
15... Diffusion part, 18... Insulating layer, stone 1 Figure
Kin Z Zu Atsushi 3 Figure

Claims (1)

[Claims] 1. At least two or more regions having equivalently different refractive indexes in the light propagation direction are alternately repeated in the range covered by the optical electric field, and the widths of these regions extend in the cavity direction. A semiconductor laser device characterized by a change in temperature. 2. The semiconductor laser device according to claim 1, wherein the repetition period of the regions having equivalently different refractive indexes is constant.