JPH06310803A - Semiconductor laser device - Google Patents

Abstract

PURPOSE:To form a high-output and low-noise semiconductor laser by a method wherein the reflectivity of the end face of the front of a resonator is specified and quantum well active layers are provided in an active layer. CONSTITUTION:The reflectivity of the end face of the front of a resonator is set at 20% or higher and 40% or lower, quantum well active layers 3a to 3c are sectioned by barrier layers 4a and 4b and light guide layers 2a and 2b are respectively provided on the outsides of the layers 3a and 3c. It is generally desirable that the thickness of the layers 3a to 3c is 1 to 20nm and a part consisting of the layers 3a to 3c, the layers 4a and 4b and the layers 2a and 2b is formed as an MQW layer. Thereby, a high output and low noise are reconciled and the laser can be formed as a high-output and low-noise laser without causing any problem in the life and the like of the laser.

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, and more particularly to a semiconductor laser device capable of high output with low noise.

[0002]

2. Description of the Related Art Semiconductor laser devices are used in various fields, but reducing noise in semiconductor laser devices is an important item required in most fields of application. As a method of reducing noise, increasing the front end face reflectance Rf has been conventionally performed.

On the other hand, in order to increase the output, it is necessary to reduce the reflectance Rf. Therefore, high output and low noise are
The requests were conflicting with each other and were in a so-called trade-off relationship.

Conventionally, for example, in a high-power semiconductor laser device, the reflectance Rf is set to 5 to 10%, while the reflectance Rf is set to 20 to 30% in order to reduce noise.

In a high-power laser, it is difficult to increase the reflectance Rf in terms of design, and if the reflectance Rf is increased to suppress noise (quantum noise), the optical density in the resonator increases, Have a significant impact on life.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a semiconductor laser device which has both a high output and a low noise and has a high output and a low noise without causing a problem in the life. .

[0007]

According to a first aspect of the present invention, a semiconductor laser device has a front end facet reflectance of 20% or more and 40% or less and a quantum well active layer. A characteristic semiconductor laser device which achieves the above object.

The invention according to claim 2 of the present application is the semiconductor laser device according to claim 1 characterized in that the optical confinement structure is a loss guide structure, and thereby achieves the above object. .

[0009]

According to the present invention, the front end face reflectance is 20%.
It has been possible to reduce the noise to 40% or less and improve the characteristics at the time of high output operation by using the quantum well active layer.

That is, in the present invention, by using the quantum well in the active layer of the high-power laser semiconductor device, it was possible to obtain a higher tolerance to the light density than the conventional structure (DH active layer). As a result, the reflectance Rf can be increased even in a high-power laser, and both high output and low noise can be achieved. This is important for applications such as optical recording disks, SHG excitation, etc. and is extremely advantageous for such applications.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. However, as a matter of course, the present invention is not limited to the embodiments.

Embodiment 1 FIG. 1 shows an outline of the structure of a semiconductor laser device of this embodiment, and FIG. 2 shows an enlarged view of this front end face. This semiconductor laser device is an example in which the present invention is applied to a GaAlAs semiconductor laser device.

This semiconductor laser device has a front end face whose reflectance is 20% or more and 40% or less, and the active layer 5E has a quantum well active layer (see 3a to 3a in FIG. 3).
3c). In FIG. 1, 6 is p
A side ohmic electrode is shown, and 7 is an n side ohmic electrode. The structure of 5A to 5G will be described later in detail with reference to FIG.

The structure of the quantum well active layer of the semiconductor laser device of this embodiment is shown in FIG. Quantum well active layers 3a, 3
b and 3c are divided into barrier layers 4a and 4b. Light guide layers 2a and 2b are provided on the outer side thereof.

In FIG. 3, x is Al _x G _1-x As at the corresponding position.
The value of x (that is, the Al content ratio) is shown. 1
0a and 10b are clad layers.

Generally, the thickness of the quantum well active layers 3a, 3b, 3c is preferably 1 to 20 nm, and the semiconductor laser device of this embodiment is designed for general laser generation with a wavelength of 790 nm, and the quantum well width is 20 nm or less is preferable. In this embodiment, the quantum well active layers 3a, 3b and 3c are 10 nm, the barrier layers 4a and 4b are 6 nm, and the optical guide layer 2 is
The thicknesses a and 2b were set to 20 nm. In this embodiment, the portion formed of the quantum well active layers 3a, 3b and 3c, the barrier layers 4a and 4b, and the optical guide layers 2a and 2b is formed as an MQW layer.

The number of quantum well active layers is preferably 1 to 5 for the high output type, and 3 in this embodiment.

Next, the laser structure of this embodiment will be described with reference to FIG. FIG. 2 is a view of the laser device as seen from the end face of the hollow.

The semiconductor laser device of this embodiment is formed as follows. MO on the n-GaAs substrate 5G
An N clad layer 5F is grown by a (metal organic) CVD method, and then an active layer 5E (comprising 2a, 2b, 3a to 3c, 4a and 4b in FIG. 3) of MQW structure is formed as an active layer 5E, and A 1P clad layer 5D and an n-GaAs current narrowing layer 5C are grown. This current narrowing layer 5C is
In this example, it is formed as a layer that serves as both light confinement and current confinement. This has a loss guide structure. Here, the loss guide structure means that a semiconductor having a band gap smaller than the oscillation wavelength is used as a confining material, and here, mainly, GaAs (Ga _0.9 Al _0.1 As) is used.
And so on) can fulfill this function. Next, a part of the current narrowing layer 5C is removed by using photolithography and RIE or wet etching to form stripes. Next, by the second MOCVD growth, the second P
The clad layer 5B and the P cap layer 5A are grown. After that, ohmic electrodes are formed on the p-side and the n-side.

In FIG. 2, light is emitted from a portion indicated by reference numeral 8.

FIG. 4 shows the structure of the optical thin film coated on the end face. The reflectance of the front end face 1 is equal to that of the Al ₂ O ₃ film 1
This is controlled by forming a laminated film containing 1 or Al ₂ O ₃ film by vapor deposition or sputtering.

Regarding the reflectance of the rear end face 1a, reference numeral 1
As shown by 2, a high-reflectance mirror is formed by forming 1 / 4λ Al ₂ O ₃ / Si in two or three cycles. Taking a laser having an oscillation wavelength λ = 790 nm as an example, the relationship between the Al ₂ O ₃ film thickness and the front facet reflectance is as shown in FIG. Therefore, in order to obtain the reflectance of 20 to 30%, it is sufficient to form the film of 1900 to 2950Å (see the hatched portion in FIG. 5). Thirty
SiO ₂ can be used together for a reflectance of more than%. When the wavelength λ is different, the film thickness is 0.24λ ~
The desired reflectance may be selected in the range of 0.38λ.
In order to obtain a reflectance of 30% or more on the front end face,
Generally, it is desirable to use a multilayer coat similar to that for the rear.

In the case of a high-power laser of a transverse single mode (used for an optical disc having a light intensity distribution of 1 peak), electrons e are consumed at a high light density, and output by spatial hole burning that does not contribute to laser oscillation. 40% is the practical upper limit of the front reflectivity, because of a decrease in the output and the end surface destruction output.

FIG. 6 shows the IL characteristic (current-optical characteristic) of the laser according to this embodiment to which the present invention is applied. This is a graph showing how much light (mw) is output when a certain amount of current (mA) is applied.

The quantum well laser (MQW) structure shows better characteristics than the conventional structure (DH) even at a reflectance of Rf = 30%.

Next, the front facet reflectivity Rf and the laser noise RIN (Relative I) in the present embodiment.
The relationship of (Nenity Noise) will be described. At a reflectance of 30%, the MQW structure of this embodiment has a value of -1.
37.0 (dB / Hz), -13 in the conventional DH structure
It was 5.7 (dB / Hz) (note that the data has high frequency superimposition, Po≈5 mw).

From this study, in order to achieve both high output (writing) characteristics and low output (5 mw to reading, usually 3 to 5 mw) noise characteristics, the quantum well structure (MQW structure) and the front end face high reflection are considered. It turns out that the combination of rates is optimal.

In the above embodiment, the dielectric film used for the end face coating is not limited to Al ₂ O ₃ , but SiO ₂ and SiN.
Etc. can be used.

Modified Example Next, a modified example will be described. As the quantum well structure (MQW structure), in addition to the structure shown in FIG. 3, one layer (3a) as shown in FIG. 7A and four layers (3a to 3d) as shown in FIG. 7B.
Alternatively, the light guide layers 2a and 2b may be formed as shown in FIG.
It is also possible to use the GRIN type as shown in FIG.

[0030]

According to the present invention, it is possible to provide a semiconductor laser device which has both high output and low noise, and which has high output and low noise without causing a problem in life. It was

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a semiconductor laser device according to a first embodiment.

FIG. 2 is an enlarged view of a front end surface of the semiconductor laser device according to the first embodiment.

FIG. 3 is a structure of a quantum well active layer of the semiconductor laser device of Example 1.

FIG. 4 is an explanatory diagram of an optical thin film used for an end surface of the semiconductor laser device according to the first embodiment.

FIG. 5 is a diagram showing a relationship between Al ₂ O ₃ film thickness and end face reflectance.

FIG. 6 is a diagram showing IL activity of a laser using a DH active layer and an MQW active layer.

FIG. 7 is a diagram showing a modified example.

[Explanation of symbols]

 1 Front end face 3a-3d Quantum well active layer 3E Active layer

Claims (2)

[Claims] 1. A semiconductor laser device having a front end facet reflectance of 20% or more and 40% or less and a quantum well active layer. 2. The semiconductor laser device according to claim 1, wherein the optical confinement structure is a loss guide structure.