JPH1022570A - Nitride semiconductor laser element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the heat radiation property of a laser element and aim at continuous oscillation by inserting a laser chip where a positive electrode and a negative electrode are made on the same side into a support which has a recess whose inner face is metallized. SOLUTION: For a laser chip, an n-type nitride semiconductor layer 2, an active layer 3, and a p-type nitride semiconductor layer 4 are stacked on a substrate 1, and a negative electrode 10, on the surface of the n layer 2 exposed by etching, and a positive electrode 11, on the surface of the uppermost p layer 4, are made. A recess to insert a laser chip is made on the surface of the support 20, and the inner face of recess is metallized with a recess metallic film 21. A laser chip is inserted in face-up condition into the recess of the support 20, and the heat conducted to the board side of the laser chip is absorbed by the recess of the support. This makes the heat generated by the active layer easy to be conducted to the support, and improves the heat radiation property of the chip. Moreover, this can improve the reliability on a laser element.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor (In).
_{X Al Y Ga 1-XY N} , 0 ≦ X, 0 ≦ Y, a laser element made of X + Y ≦ 1).

[0002]

2. Description of the Related Art A nitride semiconductor is known as a material for a laser device that emits light in the ultraviolet to blue region, and the present applicant has recently used this material to generate a laser oscillation of 410 nm at room temperature under pulse current. Announced (for example, Jpn.J.
Appl. Phys. Vol 35 (1996) pp. L74-76). The published laser is of a so-called electrode stripe type, in which laser oscillation is performed with the stripe width of the nitride semiconductor layer including the active layer set to several tens μm.

In general, a laser element is mounted on a support having a good thermal conductivity, such as a heat sink or a submount, in order to assist heat radiation of a semiconductor chip that oscillates laser.
The rise in the temperature of the semiconductor chip causes a change in the laser characteristics such as the optical output and the oscillation wavelength, and shortens the life of the entire device.

In the case of a nitride semiconductor laser device, since most of the semiconductor chips use an insulating substrate, the positive electrode and the negative electrode of the laser chip are taken out from the nitride semiconductor layer on the same side. . Such a laser chip is usually mounted on a support in a face-down or face-up state. In the case of face-down, the electrode and the support are often directly bonded via a conductive adhesive such as a solder material. In the case of face-up, the electrode and the support are often wire-bonded.

[0005]

As described above, although the nitride semiconductor laser device mounted on the support is still oscillated only by a pulse current with a small heat load, it is required to continuously oscillate. Therefore, it is necessary to further improve the heat radiation of the chip. Therefore, it is an object of the present invention to improve the heat dissipation of a laser device made of a nitride semiconductor and aim at continuous oscillation.

[0006]

According to the present invention, there is provided a laser device comprising:
A laser chip in which a positive electrode and a negative electrode are formed on the same surface side is inserted face-up into a support having a recess whose inner surface is metalized.

Furthermore, the laser chip is located at a position where the height of the negative electrode is lower than the height of the positive electrode, and the surface of the nitride semiconductor layer on which the negative electrode is formed and the end face of the concave portion of the support are substantially aligned. Preferably at the same height.

Further, an electrode pattern for connecting to an external electrode is metallized on the surface of the other support of the recess, and the negative electrode of the laser chip and the electrode pattern are connected to a continuous metal. Preferably, they are electrically connected by a film.

[0009]

FIG. 1 is a schematic sectional view showing one structure of a laser chip according to a laser device of the present invention.
3 is a schematic cross-sectional view showing one structure of a support according to the laser element of the present invention, and FIG. 3 is a schematic cross-sectional view showing the structure of a laser element in which the laser chip of FIG. 1 is mounted on the support of FIG. It is.

The basic structure of the laser chip shown in FIG. 1 is such that an n-type nitride semiconductor layer (hereinafter, referred to as an n-layer) 2, an active layer 3, and a p-type nitride semiconductor layer ( Less than,
It is called p layer. 4) are stacked, a negative electrode 10 is formed on the surface of the n-layer 2 exposed by etching, and a positive electrode 11 is formed on the surface of the uppermost p-layer 4. Is formed, and both electrodes are formed on the same surface side. Further, this laser chip has a ridge stripe type structure in which the p layer 4 above the active layer 4 is etched in a stripe shape with a width of, for example, 5 μm or less, and is formed on the p layer stripe. The positive electrode 11 is an ohmic electrode, and a pad electrode 12 is formed on the positive electrode 11 to increase the electrode area for bonding. Further, between the positive electrode 11 and the negative electrode 10, an insulating film 13 made of a high dielectric material such as SiO ₂ or Al ₂ O ₃ is formed for the purpose of preventing a short circuit between the electrodes. This figure shows a view when the device is cut in a direction perpendicular to the p-layer stripe, that is, in a direction perpendicular to the waveguide.

In the laser chip shown in FIG. 1, an insulator such as sapphire (Al ₂ O ₃ ) or spinel (MgAl ₂ O ₄ ), SiC, GaN or the like is used for the substrate. The body is often used. In the nitride semiconductor grown on the substrate, the p-layer is etched to expose the surface of the n-layer, and electrodes are provided on the uppermost p-layer and the exposed n-layer. In particular, as shown in FIG.
By adopting a structure in which the striped negative electrode 10 is formed symmetrically with respect to the striped positive electrode 11, the current can be made uniform and the threshold can be lowered.

On the other hand, the support body 20 shown in FIG. 2 has a function of disposing a laser chip and dissipating heat generated by the laser chip, and examples thereof include a heat sink and a submount mounted on the heat sink. Examples of the material of the support include diamond, AlN, SiC, CuW, BeO, and Mo.
It is desirable to select a material having a large thermal conductivity and a small coefficient of thermal expansion. Further, a concave portion having a size such that a laser chip can be inserted is formed on the surface of the support 20, and the inner surface of the concave portion is metallized with a concave metal thin film 21. For example, Au / Sn, Pb
It is preferable to form a solder material such as / Sn, In, Au / Si, or a thin film made of a metal having good conductivity such as Au, Ag, or Al. When a metal thin film is formed with a solder material, a laser chip can be directly die-bonded in a concave portion. When a thin film of Ag, Al, or the like is formed in the recess, the substrate of the laser chip and the metal thin film may be die-bonded via the solder material. Particularly preferably, when metallizing with a solder material, the solder material melted by heating goes around to the side surface of the substrate as shown in the circled portion in FIG. 3A, so that the contact area between the laser chip and the support is increased, and the heat area is increased. The conductivity is improved.

FIG. 3 is a sectional view showing a state in which the laser chip is inserted into the concave portion of the support. The negative electrode 10 is connected to another terminal by wire bonding, and the positive electrode 1 is connected to the other terminal.
Reference numeral 1 is also connected to other terminals via pad electrodes 12 by wire bonding. As described above, by inserting the laser chip into the concave portion of the support 20 in a face-up state, heat generated in the substrate of the laser chip is absorbed by the concave portion of the support. In other words, the heat of the entire chip can be quickly transmitted to the outside by absorbing the heat generated by the laser chip at the bottom of the concave portion in contact with the substrate and at the side surface of the concave portion close to or in contact with the side surface of the substrate. The heat radiation effect is improved.

[0014] More preferably, the surface of the nitride semiconductor layer on which the negative electrode 10 of the laser chip is formed and the end face of the concave portion of the support 10 are substantially at the same height. FIG. 3 shows a state in which the electrodes are connected to the external electrodes by wire bonding. However, when the negative electrode forming surface of the laser chip and the end surface of the concave portion are substantially the same, for example, the laser chip is mounted on a support such as a submount. Can be installed, and the submount can be directly bonded to the heat sink in a face-down state. In addition,
The term “substantially the same height” means that the horizontal plane between the negative electrode forming surface of the laser chip and the negative electrode forming surface of the support is within a range of ± 10 μm.

Further, when the laser chip is inserted into the concave portion of the support, it is desirable that the plane of the support is not exposed on at least one of the laser light emitting surfaces. That is, it is preferable that the support does not protrude on one of the resonance surfaces of the laser chip. This is because part of the laser light emitted from the resonance surface is reflected by the surface of the support, so that the shape of the laser light changes. Therefore, the cross-sectional view shown in FIG. 3 also shows a side view of the laser element viewed from the side of the resonance surface where the support does not protrude.

FIG. 4 is a sectional view showing the structure of another laser device according to the present invention. In this laser element, an electrode pattern 22 for connecting to an external electrode is metallized on the surface of the support other than the concave portion. The metallization of the electrode pattern can be formed by a printing method in addition to a normal vapor deposition method such as vapor deposition and sputtering, similarly to the metallization of the concave portion. Since the electrode pattern 22 is connected to an external electrode,
Alternatively, as shown in FIG. 4, the negative electrode of the laser chip having two negative electrodes is connected on the surface of the support to form one negative electrode. In the laser device of FIG. 4, since the electrode pattern 22 is connected on the surface of the support, it is shown that only one wire bonding of the negative electrode is required. Further, in the laser device of FIG. 4, the negative electrode 10 of the laser chip and the electrode pattern 22 metallized on the surface of the support 20 are connected by a continuous electrode metal film 30. When the electrodes are connected by the electrode metal film 30 in this manner, the reliability of bonding is improved as compared with the case where the negative electrode of the laser chip is directly connected by wire bonding.
This is because a laser generates a large amount of heat, so that the electrodes and chips are likely to contract and expand. This results in a burden on the contact portions of the electrodes. However, by connecting the electrodes with a metal film having a large contact area with the electrodes, the electrodes are less likely to be peeled off, so that the reliability is improved. Furthermore, since the electrode made of metal has good thermal conductivity, the heat radiation effect is also improved.

FIG. 5 is a schematic sectional view showing the structure of another laser device according to the present invention. This laser element differs from FIG. 4 in that one of the electrode patterns 22 formed on the support 20 is formed continuously up to the back side of the support. When the electrode pattern is formed in this manner, when the laser element is mounted on the submount, the electrode formed on the back surface of the submount can be die-bonded directly to the heat sink, so that the heat dissipation is further improved. Further, since the wire bonding portion is only the pad electrode 12 of the p-layer, the reliability is improved. In this figure, electrode pattern 2
2 is continuously formed on the back surface of the support 20,
It goes without saying that the electrode metal film 30 may be formed continuously on the back surface of the support 20.

[0018]

As described above, in the laser device of the present invention, since the laser chip is inserted into the support having the metallized recess, the heat generated by the laser chip is efficiently provided by the metallized metal thin recess. Can be communicated to the support. In particular, in a nitride semiconductor laser device in which the p layer above the active layer has a stripe-shaped ridge shape, heat tends to concentrate well on the ridge portion. In the laser device of the present invention, since the substrate side is buried in the recess, the ridge portion generating a large amount of heat approaches the electrode and the support, so that heat is easily absorbed by the support. For this reason, the heat generation of the active layer is easily transmitted to the support, and the heat dissipation of the chip is improved.

The reliability of the laser device is also improved by metallizing an electrode pattern on the support side and electrically connecting the negative electrode of the chip and the electrode pattern with an electrode metal thin film having a large area.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a laser chip according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a support according to one embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing a structure when the laser chip of FIG. 1 is inserted into a concave portion of the support of FIG. 2;

FIG. 4 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.

FIG. 5 is a schematic sectional view showing a structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

 1 ... substrate 2 ... n layer 3 ... active layer 4 ... p layer 10 ... negative electrode 11 ... positive electrode 12 ... pad electrode 13 ... ... insulating film 20 ... support 21 ... concave metal thin film 22 ... electrode pattern 30 ... electrode metal film

Claims (3)

[Claims] 1. A nitriding method wherein a laser chip having a positive electrode and a negative electrode formed on the same surface side is inserted face-up into a support having a recess whose inner surface is metallized. Semiconductor laser device. 2. The laser chip, wherein the height of the negative electrode is lower than the height of the positive electrode, and the surface of the nitride semiconductor layer on which the negative electrode is formed, and the end face of the concave portion of the support, 2. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser devices are substantially at the same height. 3. An electrode pattern for connecting to an external electrode is metallized on the other surface of the concave portion of the support, and the negative electrode of the laser chip and the electrode pattern are continuous metal films. The nitride semiconductor laser device according to claim 1, wherein the nitride semiconductor laser device is electrically connected by: