JP2922010B2 - Semiconductor laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device having a low operating current value used as a light source for a compact disk, a printer or the like.

[0002]

2. Description of the Related Art A conventional semiconductor laser device will be described below. FIG. 4 is a sectional view of a conventional semiconductor laser device. On an n-type gallium arsenide (GaAs) substrate 21, n
Type GaAs buffer layer is formed, and an n-type gallium aluminum arsenide (GaAlAs) cladding layer 2 is formed thereon.
3, p having GaAlAs active layer 24 and ridge 25a
There is a GaAlAs cladding layer 25 of an n-type, and an n-type GaAs current blocking layer 26 is formed in a portion other than the ridge 25a for current confinement. 27 is a p-type Ga
The As protective layer 28 is a p-type GaAs contact layer. In this structure, the p-type GaAs contact layer 2
8 is effectively confined in the ridge 25a and the GaAlAs active layer 2 below the ridge 25a.
At 4, laser oscillation occurs. The lateral mode is controlled by the n-type GaAs current blocking layer 26 having a smaller forbidden band width than the GaAlAs active layer 24 absorbing laser light in portions other than the ridge 25a, and the laser light is also confined in the ridge 25a. ing. That is, the refractive index of GaAs is G
Although higher than aAlAs, the laser light outside the ridge 25a is absorbed, so that the laser light is confined in the ridge 25a. Generally, by setting the width of the ridge 25a to about 5 μm, a single mode laser beam used for a compact disk, a printer, or the like can be obtained.

[0003]

In recent years, with the miniaturization of optical pickups, there has been a demand for a laser having a lower operating current and less heat generation. However, the above-described conventional configuration has a problem that the threshold and efficiency of the laser are limited by the loss of the waveguide due to the absorption of light in the n-type GaAs current blocking layer.

An object of the present invention is to solve the above conventional problems and to provide a semiconductor laser device having a low operating current.

[0005]

In order to achieve this object, a semiconductor laser device according to the present invention comprises a GaAs semiconductor substrate with a first semiconductor layer of GaAs or GaAlAs serving as an active layer interposed therebetween. the first larger forbidden band width than the semiconductor layer, a second of different conductivity type GaAlAs each other, is formed a third semiconductor layer, said Li Tsu di part of the second semiconductor layer is formed In the region other than the ridge shape, AlAs is deposited from the second semiconductor layer.
The fourth embodiment has a structure in which a fourth semiconductor layer made of GaAlAs having a mixed crystal ratio of about 0.05 and a conductivity type different from that of the second semiconductor layer is formed.

[0006]

With this configuration, the injection current is confined in the ridge in the fourth semiconductor layer, and laser oscillation occurs in the active layer below the ridge. Here, the refractive index of the fourth semiconductor layer is the second
Laser light is confined below the ridge, and a single transverse mode is obtained. Unlike the conventional semiconductor laser device, the laser beam is not confined by the absorption of the current blocking layer, so that the loss of the waveguide can be greatly reduced. That is, the threshold value of laser oscillation is low,
Since the efficiency is increased, the operating current value can be significantly reduced.

[0007]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of a semiconductor laser device according to one embodiment of the present invention. n-type GaAs substrate 1
An n-type GaAs buffer layer 2 is formed on
An n-type Ga _0.5 Al _0.5 As clad layer 3 and Ga
P-type G having _0.9 Al _0.1 As active layer 4 and ridge 5a
An a _0.5 Al _0.5 As cladding layer 5 is formed, and an n-type Ga _0.45
An Al _0.55 As layer 6 is formed. 7 is a p-type G
The aAs protection layer 8 is a p-type GaAs contact layer. In this structure, the p-type GaAs contact layer 8
Is effectively confined in the ridge 5a, and the Ga _0.9 Al _0.1 As active layer 3 below the ridge 5a.
Causes laser oscillation. The transverse mode laser beam is obtained by _converting the refractive index of the n-type Ga _0.45 Al _0.55 As layer 6 to the p-type Ga _0.5 A.
l _0.5 As clad layer 5 is smaller than
Trapped at the bottom of In this case, the confinement of the laser light in the lateral direction is not due to the absorption but to the difference in the refractive index of the material, so that a semiconductor laser device having a small waveguide loss and a small operating current value can be obtained.

FIG. 2 is a manufacturing process diagram of a semiconductor laser device according to one embodiment of the present invention. As shown in FIG. 2A, an n-type GaAs buffer layer 2 and an n-type Ga _0.5 A are formed on an n-type GaAs substrate 1 by MOCVD growth.
l _0.5 As clad layer 3, Ga _0.9 Al _0.1 As active layer 4, p-type Ga _0.5 Al _0.5 As clad layer 5, p-type G
An aAs protective layer 7 is formed. Next, as shown in FIG. 2B, a nitride film 9 is formed in a stripe shape, and etching is performed using the nitride film 9 as a mask to form a ridge 5a. Next, as shown in FIG. 2 (c), the pressure MOCVD method, selectively growing a Ga _{0. 45} Al _0.55 As layer 6 of n-type. Next, as shown in FIG. 2D, the nitride film 9 is removed, and a p-type GaAs contact layer 8 is grown. In this embodiment, a GaAlAs-based material is used, but another compound semiconductor material may be used.

FIG. 3 is a current-light output characteristic diagram of a semiconductor laser device according to one embodiment of the present invention. The characteristics of the conventional semiconductor laser device are also shown for comparison. As shown in FIG. 3, in the semiconductor laser device of this embodiment, since the loss of light is small, the threshold value is low, the efficiency is high, and the operating current value is small. Specifically, the operating current value for emitting a laser beam of 3 mW at room temperature is reduced to 50 m of the conventional value.
A could be reduced to 30 mA.

[0010]

As described above, the present invention provides a semiconductor device of GaAs.
GaAs or GaAlA to be an active layer on a substrate
s with the first semiconductor layer of s interposed therebetween.
GaAl with different forbidden band width and different conductivity types
Second and third semiconductor layers made of As are formed;
A ridge is formed in a part of the second semiconductor layer;
In the region other than the ridge shape, A
The ratio of As mixed crystal is approximately 0.05 large and the second semiconductor
By adopting a structure in which the fourth semiconductor layer made of GaAlAs having a conductivity type different from that of the body layer is formed, an excellent semiconductor laser device having an operation current value significantly lower than that of a conventional semiconductor laser device can be realized. Such a semiconductor laser device,
It is effective when used as a light source for compact discs and printers, for which miniaturization of optical pickups is required.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor laser device according to an embodiment of the present invention.

FIG. 2 is a manufacturing process diagram of a semiconductor laser device according to an embodiment of the present invention.

FIG. 3 is a current-light output characteristic diagram of a semiconductor laser device according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional semiconductor laser device.

[Explanation of symbols]

1 n-type GaAs substrate (semiconductor substrate) 3 n-type Ga _0.5 Al _0.5 As clad layer (third semiconductor layer) 4 Ga _0.9 Al _0.1 As active layer (first semiconductor layer) 5 p-type Ga _0.5 Al _0.5 As clad layer (second semiconductor layer) 5a Ridge 6 n-type Ga _0.45 Al _0.55 As layer (fourth semiconductor layer)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01S 3/18

Claims (1)

(57) [Claims] 1. A semiconductor device comprising a GaAs semiconductor substrate having a first semiconductor layer made of GaAs or GaAlAs serving as an active layer interposed therebetween, having a larger forbidden band width than that of the first semiconductor layer and having different conductivity types. A second made of GaAlAs,
The third semiconductor layer is formed, the part of the second semiconductor layer and Li Tsu di is formed, AlAs mixed crystal ratio than the second semiconductor layer in a region other than the ridge is substantially
A semiconductor laser device having a fourth semiconductor layer made of GaAlAs, which is 0.05 larger and has a conductivity type different from that of the second semiconductor layer.