JPH02143580A - Semiconductor laser element - Google Patents

Abstract

PURPOSE:To obtain a DFB type semiconductor laser element whose threshold current is small and oscillation spectrum is narrow by a method wherein a quantum well structure locally grown is provided to at least either the crest or the trough of a grating in an active region. CONSTITUTION:An n-InP layer 12 and a GaxIn1-xAsyP1-y layer 13 are successively formed on an n-InP substrate 11 to form a first clad layer, a grating 15 is provided to the GaxIn1-xAsyP1-y layer 13 through an interference exposure method and an etching, a quantum well line 14 of Gax.In1-x.As is grown on the crests and the troughs of the grating 15, furthermore a Gax'In1x'Asy'P1-y' layer 16, a p-InP layer 17, and a p-GaInAsP contact layer 20 are successively grown to form a second clad layer, and a p-electrode 18 and an n-electrode 19 are evaporated. The thickness of the quantum well line 14 is made equal to or less than 200Angstrom in the direction of X, and the line 14 is localized at the crests and the troughs of the grating 15 in the direction of Z, so that the quantum well line 14 is made to have a carrier trapping effect in two-dimensions X-Y.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a distributed feedback semiconductor laser device having a quantum well structure with a small dark value current and a narrow spectral line width.

[Conventional technology]

Distributed feedback type (DFB) in which a reflector composed of a diffraction grating is built inside the laser crystal.
The semiconductor laser device (Feedback) is used as a light source for high-speed optical communication because it can produce a specific single-mode oscillation. A conventional DFB type semiconductor laser device, for example, as shown in FIG.
nAsP active layer (3) and Ga1 with 1,3 momme oscillation composition
After sequentially epitaxially growing the nAsP anti-meltback layer (4), a grating (5) with a period Δ is formed.
is formed by interference exposure method and etching, further, the p-1nP layer (6) and the p-GaInAsP contact layer (7) are regrown, and finally the p-electrode (8) and the n-electrode (9) are formed by vapor deposition. do. The DFB semiconductor laser device manufactured in this manner oscillates near the Bragg wavelength determined by the period Δ. It is well known that the oscillation threshold gain 8th is a function of the coupling coefficient of the grating and the element length, and that g is a small function of KL. Therefore, in order to reduce the threshold current, it is necessary to increase K or L.

[Problem to be solved by the invention]

In a conventional DFB semiconductor laser device, there is a limit to the value of the coupling coefficient, so if the device length is kept constant, there is a limit to the minimum threshold current. Furthermore, the oscillation spectrum line becomes wider due to fluctuations in the refractive index during high-speed modulation, and there is a limit to the narrowing of the line width.

[Means to solve the problem]

The present invention has been made in view of the above points.
The purpose is to provide a DFB type semiconductor laser device with a low threshold current and a narrow oscillation spectrum.
In a semiconductor laser device in which a first cladding layer, an active region, and a second cladding layer are sequentially laminated, and a grating is formed in the first cladding layer, the active region grows locally on at least one of the peaks or valleys of the grating. A first aspect of the present invention is a semiconductor laser device characterized in that the semiconductor laser device is formed of a quantum well structure, and an active region is formed of the quantum well structure and a layered active layer adjacent to the quantum well structure. The semiconductor laser device described in 1 is a second invention.

[Effect]

According to the theory of DFB lasers, DFB oscillation requires a periodic structure in the refractive index or optical gain.

Furthermore, it is known that the threshold current when the optical gain has a periodic structure is lower than when the optical gain is uniform. In conventional DFB type semiconductor laser devices, the optical gain is uniform and DFB oscillation is utilized due to periodic changes in the refractive index induced by the grating, but in the present invention, in addition to periodic changes in the refractive index, It also makes use of periodic changes in optical gain. That is, a quantum well structure is locally formed in at least one of the peaks or valleys of the grating, thereby obtaining a periodic structure of optical gain having the same period as the grating.

[Implementation - Examples]

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 is a sectional view of a main part of an embodiment according to the present invention,
n-1nP layer (+21 and G
, az I n 1-xA S yP I-y layers are sequentially grown to form a first cladding layer, and G a
A grating 05) is formed on the layer side by interference exposure method and etching, and Gaxr rn+-x'A is formed on the peaks and valleys of the grating.
The quantum well line side of s is grown, and further GaXp r
n+-x'Asy# P, -, s layer 0ω, p-InP
Layer 07) and p-GaInAsP contact layer Q0 are sequentially grown to form a second cladding layer, and finally p-electrode 00 and n-electrode 09) are deposited. The quantum well line 04) has a thickness of 200 Å or less in the X direction, and is localized in the c peaks and valleys of the grating in the X direction, so it becomes a quantum well line that has a carrier confinement effect in the two dimensions of X-Z. ing. G a * I
n 1-XA S y P, layer side and G az#I n,
-, #A Sy#P +-y' Oω is x, y, x"
. By doing so, the light wave becomes Ga
It can be efficiently confined between x I n 1−XA SyP +−yNQTI and GaXpInk−++·As,·P1□·layer 0ω.

For example 1. ='=0.281. = =0.6.8・
=0.471. -1, the period of the grating is 230
nm, it was possible to obtain 1,5- oscillation in the spectral line below IMHz.

FIG. 2 shows another embodiment of the present invention, in which an n-1nP substrate Q
An n-1nP layer (Co., Ltd.) as a first cladding layer on Il, -
Ga1nAsP active layer (to) with various thicknesses and G
aM I n +-HA S and p +-yiia are sequentially stacked, and G a
A grating (5) is formed on the n 1-xA S yP +-y layer (2), and G a g' r n t X' A S y' P
The zero-order G
a H-T n +-x・A S y#P 1-y' layer (to), p-1nP layer (5) and P-Gal-nAs
The steps of sequentially growing a P contact layer to form a second cladding layer and finally depositing a p electrode and an n electrode are the same as in the previous example. In this example,
A constant optical gain is obtained from the active N, and periodic changes in optical gain are obtained from the quantum well lines grown in the valleys of the grating (2).

[Effects of the Invention] As explained above, according to the present invention, since the active region has a quantum well structure grown locally on at least one of the peaks or valleys of the grating, the threshold current is reduced and the quantum effect is reduced. This has the excellent effect of reducing the oscillation spectrum line width.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of an embodiment according to the present invention, FIG. 2 is a sectional view of a main part of another embodiment according to the present invention, and FIG. 3 is a sectional view of a main part of a conventional example. 1, LL, 2l-n-InP substrate, 2, 12° 22-
n-I n P layer, 3.33-Ga InAsP
Active layer, 4...Ga1nAsP anti-meltback layer, 5,15.25...Grating, 6.
17.27-=p-1nP11. 7,20°0-p
-GaInAs Pl contact layer, 88.28
...p electrode, 9,19.29...n electrode, 3.2
3...'Gaxln+-xAs, P+-y layer, 14
4...Quantum well line, 16.26...GaX・T
nA5F#P+-y#layer.

Claims (2)

[Claims] (1) In a semiconductor laser device in which a first cladding layer, an active region, and a second cladding layer are sequentially laminated on a semiconductor substrate, and a grating is formed in the first cladding layer, the active region is a peak of the grating or a second cladding layer. A semiconductor laser device comprising a quantum well structure grown locally in at least one of the valleys. (2) The semiconductor laser device according to claim 1, wherein the active region comprises the quantum well structure and a layered active layer adjacent to the quantum well structure.