JPS59167085A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To obtain the titled device of low noise by a method wherein the fourth semiconductor layer whose forbidden band width is smaller than that of the first semiconductor layer is possesed, and then the distance between the first semiconducor layer and the second one is made closer than at the other part of a band part. CONSTITUTION:A groove shallowed at the center is formed in an N GaAs substrate 1. Next, an N-Ga1-yAlyAs layer 2, an n-Ga1-XAs layer 3, a P-Ga1-yAlyAs layer 4, and a P-GaAs layer 5 are formed thereon so as to fill up the groove. Next, an electrode is formed, thus making the device as the semiconductor laser. By such a manner, the oscillation of the state of coexistence is restrained by the increase of the absorption loss of said state, leading to always single vertical mode oscillation, and accordingly the titled device of low noise action can be obtained.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a semiconductor laser.

Conventional configurations and their problems Semiconductor lasers have many advantages, such as being small, highly efficient, and capable of direct modulation by drive current.
It is useful as a light source for optical communication and optical information processing.

In order to use the semiconductor laser for these purposes, it is necessary that the transverse mode in oscillation of the semiconductor laser is stable, and at the same time, the optical intensity noise is low.

Conventional semiconductor lasers, such as the one shown in FIG.
a A s A groove is provided in the substrate 1, and n -Ga1- is formed on the groove.
yAlyAs (y=o, 4) layer 2, n-Ga1-x
AlxAs (x=o, os) active layer 3 + p G
a1. In the semiconductor laser equipped with the A ly A 5 (y=0.4) layer 4, the light generated in the active layer 3 is absorbed on both sides of the groove, resulting in an effective complex refractive index difference and light confinement. The occurrence and transverse modes are stabilized.

However, when such a semiconductor laser is operated with an optical output of several milliwatts, it may oscillate in two longitudinal modes, which generates extremely large low-frequency noise, which poses a practical problem.

OBJECTS OF THE INVENTION The present invention obviates the drawbacks of the prior art.
The purpose of this invention is to provide a semiconductor laser that suppresses the coexistence of the longitudinal mode, oscillates in a single longitudinal mode, and has low noise.

Composition of the invention In order to achieve the above purpose, the following structure is adopted.

A first semiconductor layer, and second and third semiconductor layers sandwiching the first semiconductor layer and having a larger forbidden band width and a smaller refractive index than the first semiconductor layer, and these second or third semiconductor layers. A fourth semiconductor layer is in contact with the first semiconductor layer and has a forbidden band width smaller than that of the first semiconductor layer. The structure is such that the fourth semiconductor layer is arranged closer to each other than the other portions of the band-shaped portion.

DESCRIPTION OF EMBODIMENTS A semiconductor laser according to an embodiment of the present invention will be described below. In the following embodiments, the same parts as in FIG. 1 showing the conventional example are given the same numbers.

(Example 1) As shown in FIG. 2, a groove that becomes shallower in the center is formed in an n-GaAs substrate 1. Next, as shown in FIG. 3, an n-Ga1-yAll As layer 2, an n-Ga1-xAlxAs layer 3, a p-Ga
1yA6yAs layer 4, p-GaAs layer 5. form.

Next, electrodes (not shown) are formed to form a semiconductor laser.

(Example 2) As shown in FIG. 4, a groove is formed in an n-GaAs substrate 1. On top of this, n -Gal-yA so as to completely fill the groove.
i, As layer 2 r n Ga I x A l
x As s layer 3゜p Ga 1-A Al y A
S-layers 4 are sequentially formed. Next, p G a 1-A Al
, the part directly above the center of the groove of the As layer 4 is n Ga 1
-xA ll xA s layer is removed to the extent that it is not exposed. A p-GaAs layer 5 is formed to completely fill the removed portion, and finally electrodes are placed to complete the semiconductor laser.

Note that FIG. 6a is a sectional view taken on plane B in FIG.
The figure is a cross-sectional view of plane A or plane 0 in figure 5, and figure 6.
Figure C shows a sectional view taken along plane D in Figure 5.

Effects of the Invention In the structure of the semiconductor laser of the present invention, absorption of light generated and transmitted in the active layer is large in the vicinity of the center of the groove of the substrate. On the other hand, the coexistence state of two longitudinal modes in contact with each other, ie, the amplitude of the beat, is maximum at the center of the resonator.

Therefore, in the structure of the present invention, the absorption loss of this coexisting state becomes large and the oscillation of the coexisting state is suppressed, resulting in constant single-longitudinal mode oscillation and low noise operation.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a conventional semiconductor laser, FIG. 2 is a perspective view of a substrate of a semiconductor laser according to an embodiment of the present invention, and FIG.
The figure is a perspective view of a semiconductor laser with each layer formed on the same substrate.
FIG. 4 is a perspective view of a substrate of a semiconductor laser according to another embodiment of the present invention, FIG. 5 is a perspective view of a semiconductor laser in which each layer is formed on the same substrate, and FIG. FIG. 6 is a cross-sectional view on plane A and zero in FIG. 5, and FIG. 6(C) is a cross-sectional view on plane D in FIG. 5. 1-- -n-GaAs substrate, 2...n-Ga1
-yAlyAs, 3-...n -Ga1-XA
lxAs, 4・-p-Ga1, AdyA
s, 5----p-GaAs, 6-positive electrode, 7. - negative electrode. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] a first semiconductor layer, and second and third semiconductor layers having a larger forbidden band width and a smaller refractive index than the first semiconductor layer are formed sandwiching the first semiconductor layer. , a fourth semiconductor layer is formed in contact with the second or third semiconductor layer, and at least near the center in one direction, the fourth semiconductor layer is more in contact with the first semiconductor layer than in other parts in the one direction. A semiconductor laser characterized by being formed close to a semiconductor layer.