JPH11266058A - Gallium nitride based compound semiconductor laser diode - Google Patents

Abstract

(57) Abstract: The height of a p-electrode formed on the flat top of a resonator of a flip-chip type laser diode is different from the height of an n-electrode bonded to an n-type layer. When connecting and fixing to a heat sink, all the steps of the two electrodes must be eliminated by soldering, and it is difficult to accurately connect and fix the laser diode without tilting. A semiconductor exposed by etching from an upper surface of an uppermost layer of a gallium nitride-based compound semiconductor remaining unetched at the same height as the resonator flat top other than the resonator flat top and a first partial region of the upper surface. An insulating protective film formed by exposing at least a portion of the resonator flat top through the first partial region on the surface to the resonator flat top, and an insulating protective film bonded to the exposed portion of the resonator flat top and Formed over
An electrode and an n-electrode formed over the second partial region of the semiconductor surface exposed by etching from the second partial region on the upper surface are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser diode using a gallium nitride-based compound semiconductor in which the structures of a p-electrode and an n-electrode are taken into consideration.

[0002]

2. Description of the Related Art As a prior art of a gallium nitride based compound semiconductor laser diode, for example, there is one disclosed in Japanese Patent Laid-Open Publication No. Hei 9-199787: Nitride Semiconductor Laser Device. FIG. 6 is a schematic cross-sectional view of a gallium nitride-based compound semiconductor laser diode according to the related art. 601 is a sapphire substrate, 602 is an n-type gallium nitride based compound semiconductor layer, 603 is an active layer,
4 is a p-type gallium nitride compound semiconductor layer, 605 is a p-electrode, and 606 is an n-electrode. Reference numeral 608 denotes an insulating substrate on which an electrode pattern 607 is formed in advance,
And is connected and fixed to the above-mentioned p-electrode 605 and n-electrode 606. In the cross section of this figure, the width of the contact portion of the p-electrode 605 with the p-type gallium nitride-based compound semiconductor layer 604 is
In order to cause current constriction, the width is usually very narrow, ie, 1 to 3 μm. Also, there is a large spatial step between p electrode 605 and n electrode 606.

[0003]

In the prior art,
As shown in FIG. 6, when connecting and fixing the light emitting element consisting of 601 to 606 to the heat sink consisting of 607 and 608, all the steps must be eliminated by solder 609, so that the laser diode is tilted. Easy,
There is a problem that it is difficult to connect and fix the lead frame and the heat sink at a fixed angle.

The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a laser diode which can be easily and securely connected and fixed to a lead frame or a heat sink. .

[0005]

A first means for solving the above-mentioned problems is to form a plurality of layers of a gallium nitride-based compound semiconductor on a substrate, and leave a peripheral portion thereof while leaving a resonator portion. In the gallium nitride compound semiconductor laser diode having a flip-chip structure in which the resonator is formed into a flat island, a mesa or a ridge by removing by etching, the height of the resonator is equal to the height of the resonator other than the resonator. The upper surface of the uppermost layer of the gallium nitride-based compound semiconductor remaining without being subjected to the above-described etching and the first surface of the semiconductor surface exposed by etching from the first partial region of the upper surface.
An insulating protective film formed to expose at least a portion of the resonator flat top through the partial region to the resonator flat top;
From the p-electrode joined to the exposed portion of the flat top of the resonator and formed over the insulating protective film and the second partial region on the upper surface,
And an n-electrode formed over the second partial region of the semiconductor surface exposed by the etching. Also,
A second means is the above-mentioned first means, wherein the resonator is a mesa stripe type end face light emitting type, and the flat top exposed portion of the resonator reaches both end faces of the resonator, whereby the insulating protective film is formed. This flat top exposed portion is provided so as to be divided into two. A third means is that, in the first means, the resonator is an island-shaped surface emitting type. The fourth means is that, in the above means, the height of the n-electrode is made substantially equal to the sum of the thickness of the p-electrode and the thickness of the insulating protective film. Is approximately equal to the height. A fifth means is that, in the above-mentioned means, the area of the upper flat top of the p-electrode is widened to substantially match the area of the upper flat top of the n-electrode.
A sixth means is that, in the above means, a portion of the p-electrode on the exposed portion of the flat top of the resonator is formed of a light-transmitting thin-film metal.

[0006]

FIG. 1 is a schematic sectional view showing a gallium nitride based compound semiconductor laser diode 100 according to the present invention. 101 is a sapphire substrate, 102 is an n-type gallium nitride compound semiconductor layer, 103 is an active layer, 104
Is a p-type gallium nitride-based compound semiconductor layer, 105 is a p-electrode, and 106 is an n-electrode. Reference numeral 108 denotes a heat sink on which an electrode pattern 107 is formed in advance, which is connected and fixed to the p-electrode 105 and the n-electrode 106 by solder or a conductive adhesive 109. In the cross section of this figure, the p-type gallium nitride-based compound semiconductor layer 10 of the p-electrode 105
The width of the portion in contact with 4 is very narrow, usually 1 to 3 μm, to cause current constriction. As can be seen from the figure, according to the present invention, the p-electrode 105 is connected and fixed to the heat sink 108 on which the electrode pattern 107 is formed in advance by soldering or the conductive adhesive 109.
The contact area with the solder or conductive adhesive 109 of FIG. Therefore, the p-electrode 105 can be securely connected and fixed to the heat sink 108. Also, the height of the p-electrode 105 and the n-electrode 106
Can easily be made the same, so that 101 to 10
When connecting and fixing the light emitting element composed of 6 and 110 to the substrate composed of 107 and 108, the light emitting element does not tilt.
It can be connected and fixed accurately. Further, according to the present invention, the surface area of the p-electrode 105 is much larger than the surface area of the conventional p-electrode 605, and the p-electrode 105 has a structure surrounding the resonator. Also, there is an effect that the heat generated by the heat is easily radiated to the outside.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described based on specific embodiments. Note that the present invention is not limited to the following embodiments. FIG. 2 shows a flow chart of a manufacturing process of the gallium nitride based compound semiconductor laser diode according to the present invention used for the laser diode 100 of FIG. This laser diode was manufactured in the order of (A) to (C) as follows. (A) First, a photoresist is coated on the upper surface of the uppermost layer of a gallium nitride-based compound semiconductor crystal including a sapphire substrate 101, an n-type gallium nitride-based compound semiconductor layer 102, an active layer 103, a p-type gallium nitride-based compound semiconductor layer 104, and the like. The coating was uniformly applied, and the photoresist in a predetermined region was removed by photolithography, thereby forming an etching mask 201 as shown in FIG. Then, (a)
Is dry-etched by reactive ion beam etching, and the etching mask 201
Was removed. (B) Next, an insulating protective film 110 made of SiO _{2 and having} a film thickness of about 2000 nm is uniformly formed on the upper exposed portion by electron beam evaporation. As shown in the figure, after exposing the junction portion of the p-electrode 105 and the formation portion of the n-electrode 106 on the flat top of the resonator by wet etching, the etching mask was removed.

(C) Thereafter, the p-electrode 105 and the n-electrode 106 are connected to each other in the order of (1) to (7) below as shown in FIG.
Was formed as shown in FIG. (1) A photoresist is uniformly applied to the upper exposed portion, only the portion where the p-electrode 105 is to be formed is exposed by photolithography, and evacuated to a high vacuum of the order of 10 ⁻⁶ Torr or less by a vapor deposition device. The above p exposed on the resist and exposed
A Co film having a thickness of about 15 ° is formed on a portion where the electrode 105 is to be formed, and a Co film having a thickness of about 60 ° is formed on the thin film metal layer formed of Co.
A thin film metal layer made of Au was formed. (2) Next, the sample was taken out of the vapor deposition apparatus, Co and Au deposited on the photoresist were removed by a lift-off method, and C was removed.
A thin film metal layer having a thickness of about 75 ° and two layers of o and Au was formed. (3) Thereafter, the thin film metal layer was subjected to a heat treatment in order to reduce the resistance of the p-electrode and to improve the ohmic properties at the contact surface with the flat top of the resonator. That is, the sample atmosphere was evacuated with a vacuum pump, and O ₂ gas was supplied to a pressure of 10 Pa. In this state, the atmosphere temperature was set to about 570 ° C. and heating was performed for about 4 minutes. (4) To form a thick metal layer composed of three metal layers on the thin metal layer composed of two layers of Co and Au and having a film thickness of about 75 mm formed by the above-described process, To form a window in the photoresist at the portion where the thick metal layer is to be formed. Then, nickel (Ni) with a thickness of about 500 mm
Layer, a titanium (Ti) layer having a thickness of about 600
A nickel (Ni) layer having a thickness of 0 ° is sequentially formed on the thin film metal layer by vapor deposition, and a lift-off method is employed in the same manner as in the step (2) to form a three-layer film of Ni, Ti, and Ni having a thickness of about 6100 mm. A thick metal layer was formed. As described above, Co, Au, Ni, and Ni were deposited on the insulating protective film 110 of about 2000 nm in thickness made of SiO ₂ .
A p-electrode 105 consisting of five layers of Ti and Ni and having a thickness of about 6000 ° was formed as shown in FIG.

(5) Thereafter, a photoresist is uniformly applied to the upper exposed portion, and a predetermined region for forming the n-electrode on the exposed surface by the dry etching of (A) and the upper surface of the uppermost layer of the gallium nitride-based compound semiconductor crystal. After forming a window by photolithography and evacuating to a high vacuum of the order of 10 ^-6 Torr or less, a vanadium (V) layer having a thickness of about 175 °
An aluminum (Al) layer having a thickness of about 2,000, a vanadium (V) layer having a thickness of about 500, and a nickel (Ni) layer having a thickness of about 5,000 were sequentially deposited. (6) Further, three cycles of a vanadium (V) layer having a thickness of about 500 .ANG. And a nickel (Ni) layer having a thickness of about 6000 .ANG. (7) Finally, similar to the step (2), the lift-off method
Approximately 26000 film thicknesses consisting of 10 layers of V, Al, (V, Ni) × 4
The n electrode 106 of Å was formed as shown in FIG.

A first embodiment of the present invention will be described below with reference to FIG. FIG. 3 is a perspective view of a mesa stripe type gallium nitride based compound semiconductor laser diode 300 according to the present invention. The laser diode 300 is manufactured according to the procedure shown in the above (A) to (C), and is shown in FIG.
Has the structure shown in the sectional view of FIG. However, the laser diode 30 is provided by a conventional light confinement mechanism for edge emission.
0 emits edge light when connected and configured as shown in FIG.

A second embodiment of the present invention will be described below with reference to FIG. FIG. 4 is a perspective view of an island-shaped gallium nitride based compound semiconductor laser diode 400 according to the present invention.
The laser diode 400 is manufactured by the procedure shown in the above (A) to (C), and has a structure shown in a cross-sectional view of FIG. have. However, the laser diode 400 emits surface light from the sapphire substrate 101 side by connecting and configuring as shown in FIG. 1 by a conventional light confinement mechanism for surface emission.

A third embodiment of the present invention will be described below with reference to FIG. FIG. 5 shows an island-shaped gallium nitride based compound semiconductor device 5 according to the present invention using a translucent thin film metal for the p-electrode.
00 shows a plan view (a) and a sectional view (b) thereof. p
As can be seen from FIG. 5, the electrode 505 is formed on the insulating protective film 110 made of SiO _{2 and} having a thickness of about 2000 ° and the p electrode 505 on the flat top of the resonator exposed by wet etching.
It is formed over the joint. This p electrode 505
A film of Co having a thickness of about 40 ° is formed in the above-mentioned region, and then a thin film metal layer of about 60 ° is formed on the thin film metal layer formed of Co. )-Formed by performing the same heat treatment as in (3). With this configuration, the p-electrode 505 having a thickness of about 100 ° has a light-transmitting property. As can be seen from FIG. 5, the n-electrode 506 is formed over the exposed surface by dry etching and the upper surface of the uppermost layer of the gallium nitride-based compound semiconductor crystal. This n-electrode 506
In the above region, a vanadium (V) layer having a thickness of about 200 °, an aluminum (Al) layer having a thickness of about 1000 °, a vanadium (V) layer having a thickness of about 500 °, and a nickel layer having a thickness of about 5000 Ni) layer was sequentially deposited, and further, a vanadium (V) layer having a thickness of about 500 と and a nickel (Ni) layer having a thickness of about 6000 １ were defined as one cycle, and were sequentially deposited in two cycles. .

The metal layer 520 that reflects the laser beam is a metal layer having a thickness of about 1000 ° deposited with silver (Ag). In addition, the heat sink 508 has a square-shaped hole at the upper part of the resonator (the lower part in FIG. 5B) for transmitting laser light. With the above configuration and the conventional light confinement mechanism for surface light emission, FIG.
The gallium nitride-based compound semiconductor laser diode 500 of (b) emits surface light from the light-transmitting p-electrode 505 side. The gallium nitride-based compound semiconductor laser diode 500 includes an n-electrode 506 and a p-electrode 5 formed above the upper surface of the uppermost semiconductor crystal layer excluding the upper surface of the cavity flat top.
05 is fixed with a conductive adhesive 109 such as solder or silver paste over a wide area that covers approximately one round around the square hole by the heat sink 508 having the square hole through which the laser light passes. Is excellent in stability,
It has a structure that does not easily tilt and can be securely joined and fixed.

In the first, second, and third embodiments, the insulating protective film 110 is not formed on the n-electrodes 106 and 506, but the insulating protective film 110 is formed on the n-electrode. After the formation of the electrodes 106 and 506, they may be formed over the n-electrodes 106 and 506. In this case, the insulating protective film 11
At least a portion of the n-electrode 106, 506 extending over the top flat top is subjected to the same etching as the wet etching shown in FIG.
6, 506, again exposing the upper flat top. At this time, if the insulating protective film 110 on the flat top of the resonator is wet-etched on the entire surface, the insulating protective film 110 on the flat top of the n-electrodes 106 and 506 is also wet-etched on the entire surface, and the insulating protective film on the flat top of the resonator is etched. If only a part of the n-type electrode 110 is wet-etched, the part of the insulating protective film 110 on the flat top of the n-electrodes 106 and 506 is also partly wet-etched.
According to this configuration, the p-electrodes 105 and 505 and the n-electrode 10
6, 506 can be reliably and easily secured.
If the thickness of the insulating protective film 110 is uniform, the thickness of the p-electrodes 105 and 505 is made the same as the thickness of the n-electrodes 106 and 506, so that the laser diode does not tilt.

In the above embodiment, the thickness of the silver layer is about 1000 mm.
Although the metal layer 520 for reflecting the laser beam made of (Ag) is provided by vapor deposition, the metal forming the metal layer 520 may be of any type, as long as it has a film thickness capable of reflecting light. Further, the metal layer 520 may be formed using a method other than evaporation.

The structure of the active layer 103 may be an SQW structure or an MQW structure. Further, the n-type gallium nitride-based compound semiconductor layer 102 and the p-type gallium nitride-based compound semiconductor layer 104 may each be composed of a plurality of layers.
That is, each of those layers is a cladding layer and a contact layer.
It may be composed of layers. The active layer and other layers are made of a quaternary, ternary or binary Al _x Ga _y In _1-xy N (0
≦ x ≦ 1, 0 ≦ y ≦ 1).

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a gallium nitride-based compound semiconductor laser diode 100 according to the present invention.

FIG. 2 is a flowchart of a manufacturing process of a gallium nitride based compound semiconductor laser diode according to the present invention.

FIG. 3 is a perspective view of a mesa stripe type gallium nitride based compound semiconductor laser diode 300 according to the present invention.

FIG. 4 is a perspective view of an island-shaped gallium nitride-based compound semiconductor laser diode 400 according to the present invention.

5A is a plan view of an island-shaped gallium nitride-based compound semiconductor laser diode 500 according to the present invention using a translucent thin film metal for a p-electrode, and FIG. 5B is a cross-sectional view of the laser diode.

FIG. 6 is a schematic cross-sectional view of a gallium nitride based compound semiconductor laser diode 600 according to a conventional technique.

[Explanation of symbols]

100, 300, 400, 500, 600: gallium nitride compound semiconductor laser diode 101, 601: sapphire substrate 102, 602: n-type gallium nitride compound semiconductor layer 103, 603: active layer 104, 604: p-type gallium nitride Compound semiconductor layer 105, 605: p electrode 106, 606: n electrode 107, 607: electrode pattern 108, 608: heat sink 109, 609: solder or conductive adhesive 110: insulating protective film 201: etching mask made of photoresist 505: a p-electrode made of a light-transmitting thin-film metal 508: a heat sink having a hole through which laser light passes 520: a metal layer that reflects laser light

Claims (6)

[Claims] A resonator is formed by forming a plurality of layers of a gallium nitride-based compound semiconductor on a substrate and removing a peripheral portion thereof by etching while leaving a resonator portion, thereby forming a flat island, a mesa or a ridge. A gallium nitride based compound semiconductor laser diode having a flip chip structure formed in a mold, wherein the same gallium nitride based compound semiconductor remaining at the same height as the resonator flat top other than the resonator flat top is left unetched. An upper surface of the upper layer; and a first partial region of the upper surface, a first partial region of the semiconductor surface exposed by the etching, and at least a portion of the flat top of the resonator is exposed to form the flat top of the resonator. An insulating protective film, a p-electrode joined to the exposed portion of the resonator flat top and formed over the insulating protective film, and a second partial area of the upper surface. From being formed over a second partial region of the exposed semiconductor surface by the etching n
A gallium nitride-based compound semiconductor laser diode having an electrode. 2. The resonator is of a mesa stripe type end surface light emitting type, and the exposed portion of the flat top portion of the resonator reaches both end surfaces of the resonator, thereby bisecting the insulating protective film. The gallium nitride-based compound semiconductor laser diode according to claim 1, wherein: 3. The gallium nitride based compound semiconductor laser diode according to claim 1, wherein said resonator is of an island type surface emitting type. 4. Since the thickness of the n-electrode is substantially equal to the sum of the thickness of the p-electrode and the thickness of the insulating protective film, the height of the n-electrode is The gallium nitride-based compound semiconductor laser diode according to claim 1, wherein the height of the gallium nitride-based compound semiconductor laser diode is substantially the same as the height of the gallium nitride-based compound semiconductor laser diode. 5. The semiconductor device according to claim 1, wherein the area of the upper flat top of the p-electrode is large enough to substantially coincide with the area of the upper flat top of the n-electrode. 3. The gallium nitride-based compound semiconductor laser diode described in 1. above. 6. The semiconductor device according to claim 1, wherein a portion of the p-electrode on the flat-top exposed portion of the resonator is formed of a light-transmitting thin-film metal. The gallium nitride-based compound semiconductor laser diode according to the above.