JP2001257414A - Semiconductor laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve problems regarding kink level, stability of characteristic and reliability. SOLUTION: At least one window 11 lacking a metal electrode is formed in the metal electrode 9 formed on a stripe current injection region, crossing the stripe current injection region in the width direction. As a result, stress is reduced, and a leakage current is controlled, so that the kink level is improved, characteristic is stabilized and reliability is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser, and more particularly to an improvement in reliability.

[0002]

2. Description of the Related Art A conventional semiconductor laser, for example, an AlGaInP-based 650 nm band semiconductor laser, for example, a simple refraction waveguide semiconductor laser for narrowing a current in a stripe ridge structure, is schematically shown in FIGS. As shown in the figure and the schematic cross-sectional view, an n-type GaAs substrate 1 is shown.
01, an n-type GaAs buffer layer 102, a first cladding layer 103 of n-type AlGaInP, an active layer 104 of non-doped GaInP, and a p-type AlGa
Second cladding layer 105 of InP, p-type GaInP
An intermediate layer 106 made of GaAs and a cap layer 107 made of p-type GaAs are formed by MOCVD (Metalorganic Chemical Vapor).
Deposition: formed by metal organic chemical vapor deposition. Then, the cap layer 107 and the intermediate layer 106 are
Stripe ridges 108 are formed across these thickness directions.

[0005] A first electrode 109 is entirely attached over the stripe ridge 108, and a second electrode 110 is ohmicly attached to the back surface of the substrate 101. The first electrode 109 is in ohmic contact with the cap layer 107, and the second cladding layer 105 is formed of a metal electrode that forms a Schottky barrier, for example, a metal electrode in which Ti, Pt, and Au are sequentially laminated. In this way,
The current injection is blocked by the Schottky barrier, the current is narrowed to the stripe ridge 108, and a stripe-shaped current injection region is formed in the stripe ridge 108.

[0004]

However, the semiconductor laser having this configuration has a relatively low kink level as shown in FIG. Also, in FIG. 12, as shown by curves 111, 112, and 113, which show the temporal change in the operating current of each semiconductor laser having the above-described structure, there is a case where the variation is large for each sample and the characteristic deterioration is remarkable. .

An object of the present invention is to provide a semiconductor laser capable of improving the above-described kink level, stabilizing characteristics, and thus improving reliability.

[0006]

SUMMARY OF THE INVENTION According to the present invention, a metal electrode formed on a stripe-shaped current injection region of a semiconductor laser is cut across the stripe-shaped current injection region in the width direction. One or more windows are opened.

The window of the metal electrode is provided, for example, in the vicinity of both ends in the length direction of the stripe-shaped current injection region and at least apart from the both ends, or substantially at the center in the length direction of the stripe-shaped current injection region. May be provided in the structure.

That is, the present inventor has found that the kink level can be improved and the characteristics can be stabilized in the semiconductor laser having the above-described configuration, and the present invention provides a semiconductor laser having the above-described configuration.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser according to the present invention has at least a first clad layer, an active layer, a second clad layer, and a cap layer, and a first electrode is adhered on the cap layer. One embodiment of a semiconductor laser according to the present invention will be described with reference to FIGS. In this example, a simple refraction waveguide semiconductor laser having a stripe ridge structure for narrowing the current is used.

FIG. 1 is a schematic plan view, and FIG.
It is sectional drawing on the -A line. 650n of AlGaInP system
An example of the case of forming an m-band semiconductor laser will be described. In this case, a first conductivity type, for example, an n-type GaAs buffer layer 2 and a first conductivity type, for example, an n-type GaAs buffer layer 2 are sequentially formed on a first conductivity type, for example, an n-type GaAs substrate 1. For example, a first cladding layer 3 of n-type AlGaInP, an active layer 4 of non-doped GaInP, a second cladding layer 5 of a second conductivity type, for example, p-type AlGaInP, a second conductivity type of, for example, p-type GaIn
P intermediate layer 6 and second conductivity type, for example, p-type GaAs.
The s cap layer 7 is continuously vapor-phase grown. Then, opposing mesa grooves are formed across the thickness direction of the cap layer 7 and the intermediate layer 6 while maintaining a required interval, and a stripe ridge 8 is formed between these mesa grooves.

Then, a first electrode 9 is formed on the semiconductor chip on which such a semiconductor laser device is formed, and a second electrode 10 is formed on the back surface of the base 1.

Also in this case, the first electrode 9 is in ohmic contact with the cap layer 7, and the second cladding layer 5 is formed by sequentially stacking, for example, Ti, Pt, and Au in which a Schottky barrier is formed. The Schottky barrier prevents current injection and narrows the current in the stripe ridge 8 to form a stripe current injection region in the stripe ridge 8.

The first electrode 9 made of the metal electrode covers most of the stripe ridge 8 and is formed by deposition, sputtering, or the like. In particular, in the present invention, the ridge 8, that is, the stripe shape is formed. Across the current injection region in the width direction, one or more windows 11 are opened where the metal electrodes are missing.

The windows 11 are formed, for example, by forming a pair of windows 11 near, for example, both ends of the stripe-shaped current injection region, that is, the stripe ridge 8 in the longitudinal direction, and at a distance d from each end, for example, 20 μm. For example, when the length of the semiconductor laser chip, that is, the length of the ridge 8, that is, the resonator length is, for example, about 400 μm, the semiconductor laser chip width is about 300 μm, and the ridge width is about 5 μm, the width W of the window 11 is 10 μm to 70 μm. For example, 50
μm, and the length L is 150 μm.

The optical output characteristics of the semiconductor laser having this configuration were measured as shown in FIG. The characteristics of FIG.
As is clear from comparison with the characteristics shown in FIG. 11 of the above-described conventional semiconductor laser, the laser according to the present invention is:
Its kink level is increasing.

In the above-described example, the window 11 is opened near both ends of the stripe ridge 8 of the first electrode 9. In the same semiconductor laser device as described above, the pattern of the first electrode 9 is formed. As shown in a schematic plan view in FIG. 4, the width W is, for example, similarly 10 μm to
Window 11 having a size of 70 μm, for example 50 μm, and a length L of 150 μm
Can be formed.

FIG. 5 shows the results of measuring a change in the operating current of the semiconductor laser having the above structure with the passage of time. In this case, as shown in FIG. 5, the characteristics of the plurality of semiconductor lasers were almost the same. According to this, as is apparent from comparison with the above-described conventional FIG. 12, it shows a stable characteristic, shows a constant value after a certain operation time or more, and improves reliability. .

As described above, according to the present invention, the kink level can be improved and the stability can be improved. This is considered to be due to the following reasons. That is, the kink or bending of the light output characteristic in the conventional structure occurs at a relatively low level, whereas the current narrowing to the stripe-shaped current injection region is not completely performed and the current leakage occurs. In the configuration of the present invention, by forming a portion where the electrode is missing across the first electrode 9 across the stripe-shaped current injection region, it is possible to control the current flowing into the stripe-shaped current injection region from the side of the stripe. It is thought that kink was improved by this.

Regarding the stability, when the electrode 9 is formed over the entire surface, the effect of the stress due to the difference in the coefficient of thermal expansion between the electrode 9 and the semiconductor is greatly increased. It is considered that the stress of this part is released by the formation of No. 11. The stability described above can be increased by selecting the size, for example, the width of the window 11.

In each of the above examples, the window 11 is simply opened. However, as shown in FIG. 6, the window 11 does not give a mechanical stress or the like to the semiconductor surface of the opening. It is also possible to adopt a configuration in which an insulating layer 20 such as SiO ₂ or SiN is applied, and the inside of the window 11 is protected by the insulating layer 20.

Next, an example of a method for manufacturing a semiconductor laser according to the present invention will be described with reference to FIGS. Also in this example, a case where an AlGaInP-based 650 nm band semiconductor laser is formed will be described. As shown in FIG. 7A, for example, a GaAs substrate 1 of a first conductivity type, for example, an n-type
A GaAs buffer layer 2 of a first conductivity type, for example, an n-type,
A first cladding layer 3 of a first conductivity type, for example, n-type AlGaInP, an active layer 4 of non-doped GaInP,
A second cladding layer 5 of, for example, p-type AlGaInP of the second conductivity type, an intermediate layer 6 of, for example, p-type GaInP of the second conductivity type, and a cap layer 7 of, for example, p-type GaAs of the second conductivity type are sequentially arranged, for example. The stacked semiconductor 21 is formed by continuous vapor phase growth by MOCVD.

Then, an etching mask 22 having a stripe pattern is formed on the cap layer 7 of the laminated semiconductor 21 at a portion that finally forms a stripe ridge of the semiconductor laser, that is, a current injection region. The etching mask 22 can be formed into a stripe pattern having a desired position and width by, for example, application of a photoresist layer, pattern exposure, and development processing.

As shown in FIG. 7B, the etching mask 2
Using the mask 2 as a mask, portions of the cap layer 7 and the intermediate layer 6 not covered by the mask 22 are etched to a depth transverse to the thickness direction to expose the second cladding layer 5, and the etching mask 22 A stripe ridge 8 according to the pattern is formed.

Next, as shown in FIG. 7C, the etching mask 22 is removed, and an insulating layer 20 of, for example, SiO ₂ , SiN or the like is deposited on the entire surface of the ridge 8 and covering the exposed clad layer 5. . On the insulating layer 20, the insulating layer 2
A mask 23 serving as a mask for pattern etching with respect to 0 and a lift-off mask for a metal layer used to form the first electrode 9 described later is finally formed in a portion where the window 11 is formed. The mask 23 can also be formed in a required pattern by, for example, applying, exposing, and developing a photoresist layer.

As shown in FIG. 8A, first, using the mask 23 as an etching mask, a portion of the insulating layer 2 exposed to the outside is used.
0 is removed by etching.

Next, as shown in FIG. 8B, the above-described metal layer 24 constituting the first electrode 9 is deposited and formed on the entire surface covering the mask 23 by vapor deposition, sputtering, or the like. Thereafter, the mask 23 is removed, and the metal layer 24 formed on the mask 23 is selectively removed, and the removed portion is used to remove the metal layer 24, for example, as described above with reference to FIG. 1, FIG. 2, FIG. The window 11 having the pattern described in the above is opened. In this case, a semiconductor laser covered by the insulating layer 20 can be formed in the window 11 as shown in FIG.

As mentioned above, according to the present invention, for example, Al
The characteristics of the GaInP-based semiconductor laser have been remarkably improved, but other GaN-based semiconductor lasers or AlGaAs
The present invention can be applied to an s-based semiconductor laser.

In the illustrated example, the stripe ridge, that is, a pattern in which the current injection region has a uniform width in each part, is formed in a shape having a so-called taper pattern such as a narrow pattern toward both ends. For example, various deformation patterns can be obtained according to the purpose of use and the mode.

In each of the above examples, the case where the first conductivity type is the n-type and the second conductivity type is the p-type has been described. However, the opposite conductivity type can be used. The semiconductor laser to which the present invention is applied is not limited to the semiconductor laser having the above-described structure, and is not limited to the case of a single structure, but may be applied to the above-described example such as a multi-beam semiconductor laser structure or an integrated circuit structure. The present invention is not limited to this, and various configurations can be adopted.

[0030]

As described above, the semiconductor laser according to the present invention has a configuration in which a window is simply opened in an electrode. As described above, the kink level of the light output characteristics is improved, the characteristics are made uniform, and the time dependency is improved. Thus, a semiconductor laser having stable characteristics can be formed by reducing the amount of the laser beam. Therefore, the present invention can perform a stable and highly reliable operation over a long period of time, for example, as a light source used for recording and reproduction on various recording media.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of an example of a semiconductor laser according to the present invention.

FIG. 2 is a schematic sectional view taken on line AA of FIG. 1;

FIG. 3 is a light output characteristic curve diagram of the semiconductor laser according to the present invention.

FIG. 4 is a schematic plan view of another example of the semiconductor laser according to the present invention.

FIG. 5 is a time-dependent characteristic curve diagram of an operating current of a semiconductor laser according to the present invention.

FIG. 6 is a schematic sectional view of still another example of the semiconductor laser according to the present invention.

FIGS. 7A to 7C are process diagrams (part 1) of an example of a method of manufacturing an example of a semiconductor laser according to the present invention;

FIGS. 8A and 8B are process diagrams (part 2) of an example of a method for manufacturing an example of a semiconductor laser according to the present invention;

FIG. 9 is a schematic plan view of an example of a conventional semiconductor laser.

FIG. 10 is a schematic sectional view of the semiconductor laser of FIG. 1;

FIG. 11 is an optical output characteristic curve diagram of a conventional semiconductor laser.

FIG. 12 is a diagram showing a time-dependent characteristic curve of an operating current of a conventional semiconductor laser.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Base, 2 ... Buffer layer, 3 ... 1st cladding layer, 4 ... Active layer, 5 ... 2nd cladding layer, 6
... intermediate layer, 7 ... cap layer, 8 ... stripe ridge, 9 ... first electrode, 10 ... second electrode, 1
DESCRIPTION OF SYMBOLS 1 ... window, 20 ... insulating layer, 21 ... laminated semiconductor, 22 ... etching mask, 23 ... mask,
24 ... metal layer, 101 ... base, 102 ... buffer layer, 103 ... first cladding layer, 104 ...
Active layer, 105: second cladding layer, 106: intermediate layer, 107: cap layer, 108: stripe ridge, 109: first electrode, 110: second electrode

Claims (7)

[Claims] A metal electrode formed on a stripe-shaped current injection region of a semiconductor laser has one or more windows that are cut off across the stripe-shaped current injection region in a width direction and are not provided with the metal electrode. A semiconductor laser comprising an aperture. 2. The metal electrode according to claim 1, wherein at least one pair of windows is provided near both ends in the length direction of the stripe-shaped current injection region and separated from both ends. Semiconductor laser. 3. The semiconductor laser according to claim 1, wherein at least one window of the metal electrode is provided substantially at the center in the length direction of the stripe-shaped current injection region. 4. The semiconductor laser according to claim 1, wherein the window of the metal electrode is covered with an insulating layer. 5. The semiconductor laser according to claim 1, wherein said semiconductor laser is an AlGaInP-based semiconductor laser. 6. The semiconductor laser according to claim 1, wherein said semiconductor laser is a GaN-based semiconductor laser. 7. The semiconductor laser according to claim 1, wherein said semiconductor laser is an AlGaAs-based semiconductor laser.