JPH11186662A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor laser device of a long life wherein a good heat dissipation structure is realized and light emitting property, temperature property and reliability are improve, by connecting a semiconductor laser element and an electrode terminal, and an electrode pad and an electrode terminal by a plurality of wires. SOLUTION: A semiconductor laser 10A has a semiconductor laser element 20A, electrode terminals 50, 60A and a plurality of wires 70, 70,..., and 80, 80.... A semiconductor laser element 20A is a laser element which comprises a gallium nitride compound semiconductor and has a p-side electrode 30 and an n-side electrode 40. The electrode terminals 50, 60A are electrode terminals for supplying a driving current to the semiconductor laser element 20A. The p-side electrode 30 of the laser element 20A and the electrode terminal 50 are connected by a plurality of wires 70, 70,.... The n-side electrode 40 of the laser element 20A and the electrode terminal 60A are connected by a plurality of wires 80, 80,.... As a result, heat dissipation efficiency can be improved greatly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor laser device. More specifically, the present invention relates to a semiconductor laser device including a gallium nitride-based compound semiconductor laser device, which is capable of remarkably improving heat radiation characteristics from an active layer of the device.

[0002]

2. Description of the Related Art In recent years, GaN and In have been used as materials for light emitting diodes (LEDs) and semiconductor lasers in the blue to ultraviolet region.
Devices using gallium nitride-based compound semiconductors such as GaN and GaAlN are being realized. Gallium nitride-based compound semiconductors have attracted attention because they have a direct transition-type band structure and can achieve high luminous efficiency.

A semiconductor laser using this material system is expected to be applied as a light source for high-density information processing because of its short oscillation wavelength. For example, if it is used as a light source of an optical disk recording device, it is possible to double the recording density.

[0004] In this specification, "gallium nitride-based compound _{semiconductor", Ga x Al y In z B} 1-xyz N (x
≦ 1, y ≦ 1, z ≦ 1, x + y + z ≦ 1) It is assumed that semiconductors of all compositions in which the composition ratios x, y, and z are changed within the respective ranges are included. For example, GaInN (x = 0.6, y = 0, z = 0.4) is also included in the “gallium nitride-based compound semiconductor”.

[0005]

However, the semiconductor laser using these gallium nitride-based compound semiconductors has a problem that it is difficult to efficiently release the heat generated in the active layer to the outside. Hereinafter, this problem will be described in detail.

First, taking gallium nitride (GaN) as a typical gallium nitride-based compound semiconductor as an example, its band gap energy is 3.4 eV. Therefore, the operating voltage of the semiconductor laser must be higher than that. On the other hand, in a semiconductor laser, it is required that the current be concentrated on the active layer. Therefore, even if the drive current value is the same, the light emitting diode (LED) and the semiconductor laser are significantly different in the current density.

Here, the heat value is determined by the product of the drive voltage and the drive current density. In other words, when a semiconductor laser is composed of a gallium nitride-based compound semiconductor, the amount of heat generated is larger than that of other material systems, and the generated heat is concentrated in the oscillation region of the active layer.

On the other hand, when forming a laminated structure of a gallium nitride-based compound semiconductor material, sapphire is generally used as a growth substrate. However, sapphire has a very low thermal conductivity and is not suitable for heat dissipation. Moreover, the region where the calorific value is the largest is the oscillation region of the active layer, which is usually relatively far from the substrate, but rather near the surface. Therefore, such a commonly used element configuration is not desirable in that heat is released from the substrate side.

As described above, the conventional gallium nitride-based compound semiconductor laser device has a problem that heat generated at a high density in the oscillation region of the active layer cannot be efficiently released to the outside.

The present invention has been made in view of such a point. That is, an object of the present invention is to provide a long-life semiconductor laser device in which a good heat dissipation structure is realized, thereby improving light emission characteristics, temperature characteristics and reliability.

[0011]

That is, a semiconductor laser device according to the present invention comprises a gallium nitride-based compound semiconductor, has at least one electrode pad, and an electrode terminal for supplying a current to the semiconductor laser device. And a plurality of wires for connecting the electrode pads and the electrode terminals, whereby heat can be efficiently radiated through the plurality of wires.

More specifically, the semiconductor laser device of the present invention comprises an n-type gallium nitride compound semiconductor layer, an active layer, a p-type gallium nitride compound semiconductor layer, a p-side electrode, A semiconductor laser device having an electrode; an electrode terminal for supplying a current to the semiconductor laser device;
And a plurality of wires connecting the side electrodes and the electrode terminals.
Emission can be performed efficiently through the side electrodes.

Further, the semiconductor laser device according to the present invention comprises:
A substrate, an n-type gallium nitride-based compound semiconductor layer formed on the substrate, an active layer formed on the n-type gallium nitride-based compound semiconductor layer, and formed on the active layer a semiconductor laser device having a p-type gallium nitride-based compound semiconductor layer, an n-side electrode, and a p-side electrode; an electrode terminal for supplying a current to the semiconductor laser device; the p-side electrode and the electrode terminal; And multiple wires connecting
In a laser device in which heat generated in the active layer cannot be efficiently released through the substrate, heat can be efficiently radiated through the plurality of wires. Become.

Here, the substrate is sapphire,
The plurality of wires are connected to a portion of the p-side electrode of the semiconductor laser device above the oscillation region, so that the efficiency of the laser device having a substrate with low thermal conductivity is improved. The heat can be dissipated.

Alternatively, the plurality of wires are connected along the oscillation region existing in a stripe shape of the semiconductor laser device, so that heat generated in the oscillation region of the active layer is efficiently reduced. Can be released.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, by connecting a plurality of wires to a p-side electrode of a gallium nitride based compound semiconductor laser device, heat generated at a high density in an oscillation region of an active layer of the semiconductor laser device can be efficiently generated. The present invention proposes a semiconductor laser device capable of emitting light to the outside.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic explanatory view illustrating a main part of the semiconductor laser device according to the first embodiment of the present invention. FIG. 2 is a schematic view illustrating the cross-sectional structure of the semiconductor laser device.

The semiconductor laser device 10A of the present invention includes a semiconductor laser element 20A, electrode terminals 50 and 60A, and a plurality of wires 70, 70,. These elements can be appropriately arranged on a member (not shown) such as a lead frame, a stem, a chip carrier, or an insulating substrate or a conductive substrate.

The semiconductor laser device 20A is a laser device containing a gallium nitride-based compound semiconductor, and has a p-side electrode 30.
And an n-side electrode 40.

The electrode terminals 50 and 60A are electrode terminals for supplying a drive current to the semiconductor laser device 20A.
Specific examples thereof include an inner lead portion of a lead frame (not shown), an electrode terminal of a stem, and a part of a wiring pattern formed on an insulating substrate. Further, it may be an input / output terminal of an electric element such as an amplification element, a resistance element, a capacitance element, or an inductor (not shown).

The p-side electrode 30 of the laser element 20A and the electrode terminal 50 are connected by a plurality of wires 70, 70,. Here, the number of wires 70 is not limited to the illustrated three, but may be a plurality of two or more. Further, the n-side electrode 40 of the laser element 20A and the electrode terminal 60A
Are connected by a plurality of wires 80. Here, the number of the n-side wires 80 is not limited to the illustrated example, and may be one.

According to the present invention, the laser element 2
The 0A p-side electrode 30 and the electrode terminal 50 are connected to a plurality of wires 7.
By connecting at 0, 70,..., The heat radiation efficiency can be greatly improved.

This effect is shown in FIG.
This will be described with reference to the cross-sectional view of FIG. That is, the laser element 20A is formed on a sapphire substrate having a thickness of about 60 μm with the c-plane as the main surface. First, a gallium nitride (GaN) buffer layer 10 is formed on the sapphire substrate 101A.
2 is formed thereon, and a GaN quality improvement layer 103 and an n-type GaN contact layer 104 are stacked thereon. further,
On top of this, n-type aluminum gallium nitride (A
1GaN) cladding layer 105, undoped GaN guide layer 106, active layer 10 having a multiple quantum well (MQW) structure.
7, a p-type GaN guide layer 108, a p-type AlGaN cladding layer 109, and a p-type GaN first contact layer 110 are stacked. Further, an n-type current block layer 111 for narrowing the injected current is provided in the oscillation region of the active layer, that is, the region where the current is injected and laser oscillation occurs. Then, the p-type GaN second contact layer 112 is covered so as to cover it, and the high carrier concentration p-type G
An aN third contact layer 113 is formed. Also,
An SiO ₂ film 120 is formed to protect the side surface from the n-type contact layer 104 to the p-type third contact layer.

On the p-type contact layer 113, p
A side electrode 30 is formed, and an n-side electrode 40 is formed on the n-type contact layer 104. Here, the p-side electrode 30 is formed of, for example, Pt, Ti, Pt, Au from the semiconductor side.
And a laminated structure composed of four layers. Also, n
The side electrode 40 can have a laminated structure of Ti and Au from the semiconductor layer side.

According to the present invention, a plurality of wires 70 are connected to the p-side electrode 30 of such a gallium nitride based compound semiconductor laser device 20A as shown in the figure. More specifically, the plurality of wires 70, 7
It is desirable that 0,... Be bonded along the stripe just above the stripe-shaped oscillation region L of the active layer 107.

In the gallium nitride based compound semiconductor laser device, as shown in FIG. 2, heat is generated at a high density in the oscillation region L of the active layer 107 in which the injection current is narrowed and laser oscillation occurs. Here, for example, the distance from the oscillation region L to the p-side electrode 30 in FIG. 2 is about 1 to 3 μm, while the distance from L to the lower surface of the substrate 101A is 65 μm obtained by adding the thickness of the semiconductor layer to the substrate thickness. The distance from L to the n-side electrode is about 30 μm from the horizontal dimension.
As can be understood from such a distance relationship, the p-side electrode 30 located immediately above the oscillation region L works extremely effectively as a path for releasing generated heat.

On the other hand, by connecting the plurality of wires 70, 70,..., The electric resistance can be reduced, and the capacitance and inductance can be adjusted. That is, by lowering the resistance, electric capacity, and inductance of the wire portion, the laser element can be modulated at a higher speed than before.
The information transmission speed can be increased.

Here, in the case of a laser device using a material system such as a gallium arsenide system or an indium phosphide system, if wire bonding is performed immediately above the active layer, defects are induced in the active layer, and the cause of the device deterioration is Becomes On the other hand, a gallium nitride-based compound semiconductor has a characteristic that element deterioration hardly occurs even when the defect density is relatively high. That is, the gallium nitride-based compound semiconductor-based semiconductor laser has an advantage that a plurality of wire bondings can be performed directly on the active layer without causing deterioration of the device.

Here, the diameter of the bonding wire used in the present invention may be a normal 100 μmΦ, but in consideration of the heat radiation efficiency, a larger diameter, for example, 1 μm.
It is desirable that the diameter be 50 μmΦ or more. As described above, by bonding a plurality of wires having a predetermined thickness directly above the active layer, the heat radiation can be significantly improved compared to the conventional case, and the initial characteristics and reliability of the semiconductor laser device can be improved. it can.

As a result of the experiment of the present inventor, it was found that 120 μmΦ 4
In the laser device in which the wires are bonded directly above the oscillation region, the slope efficiency in the current-emission intensity characteristics is improved by about 30% as compared with the related art. At the same time, the maximum emission intensity of the laser increased by about 15%. Further, the upper limit temperature at which a practical laser oscillation light can be obtained is 6 ° C from the conventional value of 40 ° C.
Improved to 5 ° C. For example, when used as an optical pickup of a DVD device, a laser oscillation operation at a maximum rated temperature of around 65 ° C. is often required. According to the present invention, by improving the heat radiation efficiency of the element,
By increasing the operating condition temperature as compared with the related art, the application range of the semiconductor laser device can be significantly expanded.

Further, according to the present invention, the life of the laser device can be extended. As a result of the experiment by the inventor, it was possible to obtain about three times the life as compared with the conventional single bonding.

According to the present invention, by bonding a plurality of wires, the contact resistance of the electrodes can be reduced,
The effect of improving the adhesive strength can also be obtained. That is, in the wire bonding step, the wire is normally pressed against the electrode with a predetermined load in a heated state, and ultrasonic waves are applied. By performing such wire bonding at a plurality of locations, the adhesion between the electrode and the contact layer thereunder can be improved, and at the same time, the contact resistance can be reduced. In the case of gallium nitride based compound semiconductor,
In particular, in many cases, the contact resistance and adhesion strength of the electrode on the p-side are not sufficient. Therefore, this effect of the present invention is remarkable.

According to the experiment of the present inventor, the contact resistance of the p-side electrode 30 was reduced to about 1/5 and the adhesion strength of the electrode was able to be improved by 50% as compared with the prior art.

Here, the main point of the present invention is to use a plurality of wire bondings to electrodes in a laser device using a gallium nitride compound semiconductor laser device, and does not depend on the laminated structure inside the laser device. However, in a structure in which the injection current is further reduced, such as a so-called BH (buried hetero) structure, the heat generation density in the oscillation region is further increased, so that a more remarkable effect can be obtained by applying the present invention.

Next, a second embodiment of the present invention will be described.

FIG. 3 is a schematic explanatory view showing a main part of a second semiconductor laser device 10B of the present invention.

Here, the semiconductor laser device 10B of the present invention
Are the semiconductor laser element 20B and the electrode terminals 50 and 60B.
, And a plurality of wires 70, 70,... As in the first embodiment described above, the electrode 30 and the electrode terminal 50 of the laser element 20B are connected to a plurality of wires 70, 70,.
.. are connected by

Here, the present embodiment is different from the first embodiment in that the laser element 20B is connected to the electrode terminal 60B.
Is mounted directly on the top and connected without wires. That is, the n-side electrode 40 is formed on the back surface side of the laser element 20B. This can be realized by using a conductive material for the substrate 101B of the laser element 20B. As a specific example of such a material, for example, silicon carbide (SiC) can be given. That is, by using a SiC substrate as the substrate 101B, a gallium nitride-based compound semiconductor layer having a predetermined quality of crystallinity can be epitaxially grown thereon, and a current can be passed through the substrate 101B.

Here, the crystal type of SiC used as the substrate is desirably "4H type" or "2H type" rather than the so-called "6H type". This is because the resistance to current can be reduced by reducing the hetero barrier with the gallium nitride-based compound semiconductor layer.

As the n-side electrode formed on the back surface of the substrate 101B, nickel (Ni) and gold (A)
u) can be used in this order. Alternatively, platinum (Pt) and gold (Au) may be stacked in this order. Further, an alloy of gold (Au) and germanium (Ge) or silicon (Si) can be used instead of gold (Au).

The laminated structure of the gallium nitride-based compound semiconductor formed on the substrate 101B can be substantially the same as that illustrated in FIG. Alternatively, various types of semiconductor laser devices using a gallium nitride-based compound semiconductor can be similarly employed.

In the present embodiment, the various effects described above with reference to FIG. 1 can be similarly obtained. Further, according to the present embodiment, n-side wire bonding is not required, so that the configuration can be simplified, and the effects of miniaturization of the device and simplification of the manufacturing process can be obtained.

Next, a third embodiment of the present invention will be described.

FIG. 4 is a schematic explanatory view showing a main part of a third semiconductor laser device 10C of the present invention.

Here, the semiconductor laser device 10C includes a semiconductor laser element 20C, electrode terminals 50 and 60C, and a plurality of wires 70, 70,... As in the first embodiment described above, the electrode 30 of the laser element 20C and the electrode terminal 50 are connected by a plurality of wires 70, 70,.

Here, also in this embodiment, similarly to the above-described second embodiment, the n-side electrode 40 is formed on the back surface side of the laser element 20C, and is directly mounted on the electrode terminal 60C via a wire. Connected without. However, in the present embodiment, the laser element 20C
Does not have a substrate. That is, it is composed only of a laminated structure of a gallium nitride-based compound semiconductor.

For example, the laser element 20C can be a laminated structure above the contact layer 104 shown in FIG. Such a laser element 20C is obtained by forming a laminated structure on a substrate (not shown) and then removing the substrate. Specifically, sapphire or Si
A layered structure of a gallium nitride-based compound semiconductor is epitaxially grown on a substrate such as C via a crystal layer that is easily etched under specific etching conditions. Thereafter, the substrate and the stacked structure can be separated by etching away the crystal layer which is easily etched. Such a crystal layer that is easily etched under specific etching conditions is, for example, ZnO, SiO
₂ , MgO, AlN and the like.

After the substrate is removed, the n-side electrode 40 is formed on the back surface of the device by exposing the n-type contact layer 104 on the back surface of the device by etching and removing the buffer layer and the quality improvement layer. Can be. Alternatively, the buffer layer or the quality improvement layer may be given an appropriate amount of doping to function as an n-type contact layer.

In the present embodiment, the various effects described above with reference to FIG. 1 can be similarly obtained. Further, according to the present embodiment, n-side wire bonding is not required, so that the configuration can be simplified, and the effects of miniaturization of the device and simplification of the manufacturing process can be obtained.

In addition to the example shown in FIG. 4, in a laser device having no substrate, a part of the n-type contact layer 104 is exposed as in the case of FIG.
It may be formed above the mold contact layer 104. In this case, as in the case of FIG. 1, the electrode terminal 60C may be provided at a position different from the laser element 20C, and may be connected to the n-side electrode 40 via a wire.

Next, a fourth embodiment of the present invention will be described.

FIG. 5 is a schematic explanatory view showing a main part of a fourth semiconductor laser device 10D of the present invention. Here, the semiconductor laser device 10D includes a semiconductor laser element 20D, electrode terminals 50 and 60D, and a plurality of wires 70, 70,.
, And a plurality of wires 80, 80,... Similarly to the first embodiment described above, the electrode 30 and the electrode terminal 50 of the laser element 20D are connected to a plurality of wires 70, 70,
.. Are connected. Also, the laser element 20D
The electrode 40 and the electrode terminal 60D are connected to a plurality of wires 80,
80,...

In this embodiment, the wire bonding of the electrode 30 is not formed immediately above the oscillation region L. The reason will be described below. That is, in the case where a sapphire substrate is used as the substrate 101A of the laser element, the sapphire is insulative, so that a part of the structure in which the gallium nitride-based compound semiconductor is stacked is removed by etching to secure the n-side contact. Is common. At this time, a current component flowing in a direction parallel to the laminating plane always occurs. The distance also depends on the thickness, resistivity, and structure of the layer structure, but generally, if the distance is too long, the resistance in the lateral direction increases accordingly, which is not desirable from the viewpoint of reducing the resistance. Further, it is not desirable that the length is too short from the viewpoint of the influence of damage to the oscillation region due to the controllability of the etching or the occurrence of a leak current due to the rising of the electrode metal due to the controllability of the electrode forming process.

For the reasons described above, it may be desirable to set the oscillation region L at a distance from the side surface 90 of the mesa region to about 10 to 20 μm. In such a case, if wire bonding is performed immediately above the oscillation region L, the bonding may wrap around to the side surface 90 and the adhesion may be reduced. Therefore, it is necessary to perform the bonding so as to be separated from the side surface 90 so as not to cause the wraparound of the bonding and to be as close as possible directly above the oscillation region L. FIG. 5 shows such a structure. That is, when the structure illustrated in FIG. 2 is used, the heat radiation is reduced by about 20% as compared with the case where bonding is performed immediately above the oscillation region, but a certain effect can be obtained without departing from the gist of the present application. It is possible to obtain.

The embodiment of the invention has been described with reference to specific examples. However, the present invention is not limited to these specific examples.

For example, the number of wires connected to the electrode 30 of the laser element is not limited to the three shown in the drawing.
It can be appropriately determined in consideration of the dimensions of the laser and the wire, the amount of heat generated in the active layer, and other various parameters.

The substrate 101 of the laser element 20A is not limited to sapphire, but may be other than SiC, Si, Ga.
Various materials such as As can be used. However, according to the present invention, a more remarkable effect can be obtained when a substrate having low thermal conductivity is used. Examples of such a substrate include, in addition to the above-described sapphire, spinel, ScAlMgO ₄ , (LaSr) (AlTa) O ₃
And the like. Here, ScAlMgO ₄
In the case of a substrate, the (0001) plane, (LaSr) (Al
Ta) In the case of an O ₃ substrate, it is desirable to use the (111) plane.

The structure of the laser element and its conductivity type are not limited to the above-described specific examples, and may be, for example, a structure in which the p-type and the n-type are inverted.

[0059]

The present invention is embodied in the form described above, and has the following effects.

First, according to the present invention, the heat radiation of the laser element can be improved by performing a plurality of wire bondings immediately above the oscillation region of the active layer. As a result, various characteristics of the semiconductor laser device can be improved, reliability and life can be extended, and the range of application can be greatly expanded.

Further, according to the present invention, by bonding a plurality of wires, the contact resistance and adhesion strength of the electrodes of the laser element can be improved. As a result, the drive current can be reduced, the light emission characteristics can be stabilized, and the mechanical strength against vibration and impact can be improved.

By connecting a plurality of wires, it is possible to reduce the electric resistance and to adjust the capacitance and the inductance. In other words, it is possible to operate the gallium nitride-based compound semiconductor laser at a high output while suppressing the heat generation of the wire, and to modulate the laser element at a higher speed than before, thereby increasing the information transmission speed. become able to.

As described above, according to the present invention, a semiconductor laser device having high performance and high reliability can be provided, and industrial advantages are great.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram illustrating a cross section of a laser element 20A.

FIG. 3 is a schematic explanatory view of a semiconductor laser device according to a second embodiment of the present invention.

FIG. 4 is a schematic explanatory view of a semiconductor laser device according to a third embodiment of the present invention.

FIG. 5 is a schematic explanatory view of a semiconductor laser device according to a fourth embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 10A, 10B, 10C, 10D Semiconductor laser device 20A, 20B, 20C, 20D Semiconductor laser element 30, 40 electrode 50, 60 electrode terminal 70, 80 wire 90 mesa side surface 101A substrate 102 buffer layer 103 quality improvement layer 104 contact layer 105, 109 clad layer 106, 108 guide layer 107 active layer 110 first contact layer 111 block layer 112 second contact layer 113 third contact layer 120 protective film L oscillation region

Claims (5)

[Claims] A semiconductor laser device including a gallium nitride-based compound semiconductor and having at least one electrode pad; an electrode terminal for supplying a current to the semiconductor laser device; and a plurality of electrodes connecting the electrode pad and the electrode terminal. A semiconductor laser device comprising: a wire; 2. An n-type gallium nitride-based compound semiconductor layer;
An active layer; a p-type gallium nitride-based compound semiconductor layer;
A semiconductor laser element having a side electrode and an n-side electrode; an electrode terminal for supplying a current to the semiconductor laser element; and a plurality of wires connecting the p-side electrode and the electrode terminal. A semiconductor laser device characterized by the above-mentioned. 3. A substrate, an n-type gallium nitride-based compound semiconductor layer formed on the substrate, an active layer formed on the n-type gallium nitride-based compound semiconductor layer, A semiconductor laser device having a p-type gallium nitride-based compound semiconductor layer formed thereon, an n-side electrode, and a p-side electrode; an electrode terminal for supplying current to the semiconductor laser device; and the p-side electrode And a plurality of wires connecting the electrode terminal and the electrode terminal. 4. The semiconductor device according to claim 3, wherein the substrate is sapphire, and the plurality of wires are connected to a portion of the p-side electrode of the semiconductor laser device above an oscillation region. 13. The semiconductor laser device according to claim 1. 5. The semiconductor laser device according to claim 4, wherein said plurality of wires are connected along said oscillation region existing in a stripe shape of said semiconductor laser element.