JP2713445B2 - Semiconductor laser device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a distributed feedback semiconductor laser device having a quantum well structure having a small threshold current and a narrow spectral line width.

[Conventional technology]

A distributed feedback (DFB) semiconductor laser device in which a reflector composed of a diffraction grating is built in a laser crystal is used as a light source for high-speed optical communication because a specific single longitudinal mode oscillation can be obtained. You. Conventional DFB type semiconductor laser devices are, for example, as shown in FIG.
On an InP substrate (1), an n-InP layer (2), a GaInAsP active layer (3) having an oscillation composition of 1.55 μm, and GaIn having an oscillation composition of 1.3 μm
After sequentially growing the AsP anti-melt back layer (4) by epitaxial growth, a grating (5) having a period Λ is formed by an interference exposure method and etching.
-Regrow the InP layer (6) and the p-GAInAsP contact layer (7), and finally form a p-electrode (8) and an n-electrode (9) by vapor deposition. The DFB semiconductor laser device manufactured in this manner oscillates in the vicinity of the Bragg wavelength determined by the period Λ. The oscillation threshold gain g _th is a function of the coupling coefficient K of the grating and the element length L,
It is well known that g _th is a monotonically decreasing function of KL. Therefore, to reduce the threshold current, it is necessary to increase K or L.

[Problems to be solved by the invention]

In the conventional DFB type semiconductor laser device, the value of the coupling coefficient K has a limit. Therefore, if the device length L is fixed, the minimum threshold current is limited. Also, the oscillation spectral line width becomes wider due to the fluctuation of the refractive index during high-speed modulation, and there is a limit in narrowing the line width.

[Means for solving the problem]

The present invention has been made in view of the above points, and an object thereof is to provide a DFB type semiconductor laser device having a low threshold current and a narrow oscillation spectrum width. In a semiconductor laser device in which a first cladding layer, an active region, and a second cladding layer are sequentially stacked on a semiconductor substrate, and a grating is formed in the first cladding layer, the active region has at least a peak or a valley of the grating. A semiconductor laser device comprising a quantum well structure locally grown on one side according to the first invention, wherein an active region comprises the quantum well structure and a layered active layer adjacent to the quantum well structure. A second aspect of the present invention is a semiconductor laser device according to the first aspect.

[Action]

According to DFB laser theory, DFB oscillation requires a periodic structure in refractive index or optical gain. It is known that the threshold current when the optical gain has a periodic structure is lower than that when the optical gain is uniform. In the conventional DFB type semiconductor laser device, the optical gain is uniform, and the DFB oscillation due to the periodic change in the refractive index induced by the grating is used. In the present invention, in addition to the periodic change in the refractive index, The periodic change of the optical gain is also used. That is, a quantum well structure is locally formed on at least one of the peaks and valleys of the grating, and a periodic structure of optical gain having the same period as the grating is obtained.

〔Example〕

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a cross-sectional view of a main part of an embodiment according to the present invention. An n-InP layer (12) and a Ga _x In layer are formed on an n-InP substrate (11).
_{1-x As y P 1-} y layer (13) sequentially to thereby form a first cladding layer by growing _{a, Ga x In 1-x As} y P 1-y layer (13) in interference exposure method and a grating etched (15) is formed, and Ca _x InIn _1-x AsAs quantum well lines (1
4) is grown, and a Ca _x ″ In _1-x ″ As _y ″ P _1-y ″ layer (16), a p-InP layer (17) and a p-GaInAsP contact layer (20) are sequentially grown. A second clad layer is formed, and finally, a p-electrode (18) and an n-electrode (19) are deposited. Since the quantum well line (14) has a thickness of 200 ° or less in the X direction and is localized at the peaks and valleys of the grating (15) in the Z direction, the quantum well line has a carrier confinement effect in two dimensions of XZ. It is a line. Ga _x I
_{n 1-x As y P 1} -y layer (13) and the _{Ca x "In 1-x"} As y "P 1-y" layer (1
6), by appropriately selecting x, y, x ″, and y ″, the energy gap can be increased with the n-InP layers (12) and (17) and the quantum well line (1).
In the middle of the energy gap of 4), make the refractive index higher than that of the InP layers (12) and (17). _{Ga x In 1-x As y} P 1-y layer light waves by doing so (13) and the _{Ca x "In 1-x"} As y "P 1-y"
It can be efficiently confined between the layers (16).

For example, _x = _x ″ = 0.28, _y = _y ″ = 0.6, _x ′ = 0.4
7, _y '= 1 and the grating period is 230nm
An oscillation of 1.5 μm with a spectral line width of 1 MHz or less was obtained.

FIG. 2 shows another embodiment of the present invention, in which an n-InP substrate (2
1) An n-InP layer (22) as a first cladding layer, a GaInAsP active layer (33) having a uniform thickness, and a Ga _x In _1-x As _y P _1-y
The layers (23) are sequentially stacked, and the Ga _x In
_{1-x As y P 1-} y layer (23) to form a grating (25) on, the valleys of the grating _{(25) Ca x 'In 1} -x' A
A quantum well line (24) of s _y 'P _1-y ' is formed. Then C
_{a x "In 1-x"} As y "P 1-y" layer (26), a p-InP layer (27) and p-GaInAsP contact layer (30) sequentially grown by the second cladding layer, and finally The deposition of the p-electrode (28) and the n-electrode (29) is the same as in the previous embodiment.
In this embodiment, a constant optical gain is obtained from the active layer (33),
Quantum well wires (2
From 4), a periodic change in the optical gain is obtained.

〔The invention's effect〕

As described above, according to the present invention, since the active region has a quantum well structure locally grown on at least one of the peaks and valleys of the grating, the threshold current is reduced, and the oscillation spectrum line width is reduced due to the quantum effect. Has an excellent effect of reducing

[Brief description of the drawings]

FIG. 1 is a sectional view of a principal part of one embodiment according to the present invention, FIG. 2 is a sectional view of a principal part of another embodiment according to the present invention, and FIG. 3 is a sectional view of a principal part of one conventional example. 1,11,21 ... n-InP substrate, 2,12,22 ... n-InP layer, 3,33 ... Ga
InAsP active layer, 4 ... GaInAsP anti-melt back layer, 5,1
5,25… Grating, 6,17,27… p-InP layer, 7,20,30
... p-GaInAsP contact layer, 8,18,28 ... p electrode, 9,19,2
9 ... n electrode, 13,23 ... Ga _x In _1-x As _y P _1-y layer, 14,24… quantum well line, 16,26… Ca _x ″ In _1-x ″ As _y ″ P _1-y "layer.

Claims (2)

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