JP2003179297A - Gallium nitride based compound semiconductor laser - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gallium nitride based semiconductor laser suitable for long time use and exhibiting excellent heat dissipation properties and a long lifetime. <P>SOLUTION: The gallium nitride based semiconductor laser comprises a plurality of gallium nitride based semiconductor layers formed on a substrate, and opposite pad electrodes formed on the gallium nitride based semiconductor layer side. It is bonded to a heat sink on the substrate side and at least one pad electrode is bonded with at least one metal wire for heat dissipation in addition to a metal wire for conduction. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gallium nitride compound semiconductor laser having improved heat dissipation.

[0002]

2. Description of the Related Art Today, a semiconductor laser using a nitride semiconductor is required to be used in an optical disk system capable of recording / reproducing information with a large capacity and a high density such as a DVD. In particular, next-generation DV that handles digital image data
A blue laser having a short wavelength is considered to be indispensable for D. A gallium nitride-based semiconductor compound laser is the most promising blue semiconductor laser.

The application range of gallium nitride-based compound semiconductor lasers will be further expanded in the future. For that purpose, there is an increasing demand for a laser capable of high output, long life and stable output.

[0004]

A laser used at high power tends to have a short life, which is partly due to the high heat generated during laser oscillation. A laser that has reached a high temperature is prone to deterioration such as a proliferation of defects in the device and destruction of the end face. Especially, if a laser with poor heat dissipation is continuously used for a long time at a high output, the life of the laser shortens remarkably.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a gallium nitride-based compound semiconductor laser having good heat dissipation, long life, high output, and suitable for long-term use.

[0006]

A gallium nitride-based compound semiconductor laser of the present invention has a structure in which a plurality of gallium nitride-based compound semiconductor layers are stacked on a substrate, and bipolar electrode pads are formed on the gallium nitride-based compound semiconductor side. The laser chip is bonded to the heat sink on the substrate side, and at least one metal wire for heat radiation is bonded on the pad electrode in addition to the metal wire for the purpose of conducting electricity.

Since the radiating fin according to the present invention is formed of a metal wire, it has a feature that it has a large surface area in spite of its small volume and that the cooling medium flows without delay because it has no dents on the surface. Have Further, the efficiency of heat dissipation can be improved by using the conductive path as the heat discharge path.

Further, it is preferable that the heat radiation fin is adhered to the pad electrode by using a wire bonding method capable of ensuring good adhesion. There is also an advantage that the radiation fin can be formed in the same process as the wire bonding of the current-carrying metal wire. At this time, the metal wire used for the current wire bonding may be used as it is for heat dissipation, or a different metal wire may be used. It is more preferable that the metal wire forming the heat radiation fin is a gold wire made of gold having good thermal conductivity.

When the heat radiation fin is formed on the pad electrode immediately above the active region, the distance between the heat radiation fin and the heat source is shortened, and the heat radiation efficiency is improved. That is, of the metal wires for heat dissipation
At least one of them is preferably adhered immediately above the active region. If a heat-dissipating metal wire is bonded directly above the active area,
Since defects are introduced into the active region due to heat and vibration during bonding, it is preferable to form the pad electrode thick to mitigate the influence during bonding. In particular, it is preferable that the pad electrode is formed to have a thickness of 0.5 μm or more because a remarkable effect can be obtained.

In the gallium nitride-based compound semiconductor laser of the present invention, it is preferable that the pad electrode to which the metal wire for heat dissipation is adhered contains gold. For example, in gallium nitride-based compound semiconductor lasers, the pad electrode is often formed by laminating a plurality of metal films. Therefore, in the pad electrode to which the heat radiation fin is bonded, at least one of the plurality of metal layers is made of a heat conductive material. It is preferable that it is made of highly-precious gold. Further, among the plurality of metal layers forming the pad electrode, it is preferable to form the gold layer in a particularly thick film because the pad electrode has good thermal conductivity.

When the gallium nitride compound semiconductor laser has a ridge stripe structure, the p-pad electrode is
It is preferably formed so as to cover the steps of the ridge stripe structure and have a substantially flat surface. If there is a step due to the ridge stripe, it may be difficult to form a heat radiation fin at a vertical portion or an inclined portion connecting the upper flat portion and the lower flat portion of the step. Therefore, in a gallium nitride-based compound semiconductor laser having a ridge stripe structure, the number of radiating fins that can be formed is smaller than that in a laser having another stripe structure, and the heat radiation efficiency may be relatively low. Therefore, if the p-pad electrode is formed so that both sides of the ridge are thick and the surface thereof is flat,
The number of radiating fins formed can be increased.

Here, two types of heat radiation fins that can be formed by wire bonding will be illustrated. One is a heat radiation fin formed by adhering one end of a metal wire to a pad electrode and cutting the metal wire leaving a length of 50 μm to 500 μm. Metal wire pieces
The heat dissipation fin has a form protruding from the surface of the pad electrode, and such a heat dissipation fin is called a throw-away type heat dissipation fin. Another example is a radiation fin formed by adhering one end onto a pad electrode with a first bond and adhering the other end onto a stem with a second bond, and cutting the fin, which has the same form as a wire bond for energization. . Such a radiation fin is called a loop type radiation fin. The radiating fin that can be used in the present invention is not limited to the above two shapes, and any shape of metal wire can be applied as long as it does not cause an electrical short circuit.

The discarding type heat radiation fins are preferable because they have a shape that can be easily formed densely and a large number of heat radiation fins can be formed. In addition, even when a large number of waste heat radiation fins are formed densely, there is a sufficient gap between the tips of the adjacent heat radiation fins for the cooling medium to pass through, so that the heat radiation performance is good. preferable.

In the discarding type radiation fin, the heat dissipation is improved because the surface area becomes large when the fin tip is formed long, but if it is made too long, there is a possibility of electrical short circuit and adhesion to the pad electrode. The parts may peel off due to mechanical load. Therefore, the preferred length is 50 μm or more 5
00 μm or less, more preferably 50 μm or more 15
It is 0 μm or less.

Since the other end of the loop type radiation fin is adhered to the stem electrode, heat radiation is promoted through the stem and the heat radiation effect is enhanced, so that it is a preferable form as the radiation fin. That is, the radiation fin is
More preferably, one end thereof is bonded to the pad electrode and the other end is bonded to the stem electrode. If it is difficult to form all the radiation fins in the loop type, the loop type and the discarding type may be mixed and formed.

Since the number of radiating fins that can be formed depends on the area of the pad electrode, the wider the area of the pad electrode, the better. Therefore, it is preferable that the total area of the n-pad electrode and the p-pad electrode is 80% or more of the upper area of the laser chip.

Further, it is preferable that the area of the p pad electrode is formed to be 60% or more of the upper area of the laser chip. Since the p-type gallium nitride-based compound semiconductor has a high resistivity, the p-type gallium nitride-based compound semiconductor layer is formed as a thin film to reduce the threshold voltage. Therefore, the p pad electrode and the active region are close to each other, and the heat radiation effect is higher when the heat radiation fin is formed on the p pad electrode than when it is formed on the n pad electrode. Therefore, it is preferable to increase the area of the p pad electrode and increase the number of heat radiation fins provided thereon, since the heat radiation effect is improved.

When the radiation fin of the present invention is used in air cooling,
It is desirable that the air contacting the radiating fins be sufficiently circulated. Therefore, it is more preferable that a structure such as a cap that seals the laser element is not provided, and that an air cooling fan is further provided to blow air to the laser chip and forcibly circulate air. Furthermore, the wind generated by the air-cooled fan is concentrated and guided to the laser chip,
In order to improve the heat dissipation efficiency, it is more preferable to include a plurality of air guide plates that are arranged so as to be widened from the laser chip toward the air cooling fan.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a schematic view of a laser 1 according to an embodiment of the present invention. A plurality of gallium nitride-based compound semiconductor layers are stacked on the substrate, and the pad electrodes 38 and 3 of both electrodes are provided on the gallium nitride-based compound semiconductor layer side.
The laser chip 3 formed with 9 is mounted on the heat sink 2 on the surface on the substrate side. On the pad electrode, the metal wire 130 for energization and the heat radiation fin 11 of the throw-away type
0 is formed.

Since the conductive path for laser oscillation is also effective as a heat conductive path, the heat generated in the active region reaches the pad electrode via the conductive path. Heat dissipation fin 110
Is formed on the pad electrode and radiates heat from the inside of the laser chip to an external cooling medium. In order to dissipate heat more efficiently, it is preferable that the cooling medium flows on the surface of the radiation fins 110 without delay. In the heat dissipation fin 110 according to the present invention, since the surface is not dented, there is no place where the cooling medium stays, and because there is a gap between the adjacent heat dissipation fins 110, the cooling medium easily flows. Therefore, the gallium nitride-based compound semiconductor laser of the present invention provided with the radiation fin formed of the metal wire has a significantly improved radiation efficiency as compared with the conventional laser.

It is preferable to use wire bonding as the bonding method of the radiation fins 110 because the radiation fins 110 make good contact with the pad electrodes to improve the radiation performance. A method such as thermocompression bonding, ultrasonic wire bonding, and ultrasonic combined thermocompression bonding can be applied to the radiation fin 110.

The radiating fin 110 is formed of a metal wire, but it is more preferably formed of a gold wire having good thermal conductivity.
When a gold wire is used as the current-carrying metal wire 130, the current-carrying gold wire and the heat radiation fins may be formed at the same time to shorten the process and the manufacturing time.

Further, if at least one of the heat radiation metal wires is bonded directly above the active region, the heat radiation fins are installed close to the active region, so that heat generated in the active region is generated. It is preferable because it is smoothly conducted to the radiation fin 110.

Since the pad electrode has a function of suppressing the generation of defects in the crystal due to heat or vibration when the heat radiation fin is bonded, when the heat radiation fin is formed immediately above the active region, the pad electrode should be made particularly thick. It is desirable to suppress the occurrence of defects in the active region. At this time, the pad electrode has a thickness of 0.
The thickness of 5 μm or more is preferable because the effect of reducing damage to the active region becomes remarkable.

In the gallium nitride-based compound semiconductor laser of the present invention, the n pad electrode 39 is formed of a laminated body of metal films selected from Ni, Ti, Au, etc., and the p pad electrode 38 is RhO, Pt, It is formed of a laminated body of metal films selected from Au or the like. In order to improve heat dissipation, the pad electrode to which the heat dissipation fan 110 is bonded preferably includes a film made of gold having high thermal conductivity.
That is, it is preferable that the pad electrode to which the metal wire for heat dissipation is adhered contains gold. Furthermore, increase the gold film thickness,
Increasing the gold content of the pad electrode is preferable because it improves the thermal conductivity of the pad electrode.

When the number of radiating fins 110 to be formed is increased, the total surface area of the radiating fins is increased and the heat radiation effect is improved. Therefore, it is desirable to form a wide pad electrode to which the heat radiation fins 110 are bonded and to form a large number of the heat radiation fins 110. In the conventional laser, the pad electrode has only to have an area capable of adhering the current-carrying metal wire, and the sum of the areas of the p-pad electrode 38 and the n-pad electrode 39 is about 50 to 60% of the upper area of the chip. Was the ratio. In the present invention, it is preferable that the pad electrode is widely formed so that the ratio is 80% or more.

Further, in order to increase the number of heat radiation fins 110 bonded to the p pad electrode 38, the p pad electrode 38
It is preferable to widen the area. Since the p-type gallium nitride-based compound semiconductor has a large electric resistance, it is formed in a thin film to suppress the device resistance to a low level. Therefore, the p pad electrode and the active region are formed very close to each other, and as a result, the heat radiation fin on the p pad electrode 38 has a higher heat radiation effect than the heat radiation fin on the n pad electrode 39. That is, in order to increase the number of heat radiation fins on the p-pad electrode, the p-pad electrode 38 may be formed wide, and the ratio of the area where the p-pad electrode 38 is formed is 60% or more of the surface area of the laser chip. It is preferably formed as follows.

FIG. 2 shows a throw-away type heat radiation fin 11
It is an enlarged view of an example of 0. In normal wire bonding, a metal wire is used to connect the electrode of the laser chip and the electrode terminal of the stem with two bonds. When forming the discarding fin without changing the setting of the wire bonder, by shortening the metal wire drawn between the first bond and the second bond, and by making the first bond and the second bond at the same position. One adhesive part 111 is formed. The shape of the adhesive portion 111 of the heat dissipation fin 110 formed in this way is 2 as shown in the figure.
It becomes a shape that two balls are stacked and crushed. Further, the metal wire between the first bond and the second bond is the bonding portion 111.
It is captured by and does not appear in the external shape. After forming the bonding portion 111, while raising the metal wire from the capillary of the wire bonder, the capillary is lifted in the direction perpendicular to the bonding surface,
Further, the fin tip portion 112 is formed by cutting the metal wire leaving a predetermined length. When the fin tip portion 112 is formed by cutting the metal wire after the second bond, the end portion has a tapered shape as shown in FIG.

A large number of heat radiation fins is preferable because the total surface area of the heat radiation fins per laser can be increased in proportion to the number of heat radiation fins. As can be seen from FIG. 2, the shape is suitable for dense formation, and has an advantage that many heat radiation fins can be easily formed. Further, even when a large number of radiating fins are formed, there is a sufficient gap between the adjacent fin tips 112 to allow the cooling medium to pass therethrough. It can be said that there is.

The surface area of the discarding type heat radiation fin 110 can be adjusted by the length of the fin tip 112.
The longer the fin tip 112 is formed, the better the heat dissipation performance of the heat dissipation fin 110. However, if the fin tip 112 is too long, there is a possibility of electrical short circuit and the adhesive portion 111 may be peeled off due to mechanical load. The preferable length is 50 μm or more and 500 μm or less, and the more preferable range is 50 μm or more and 150 μm or less.

When the laser having the radiation fin according to the present invention is used in air cooling, it is desirable that the air contacting the radiation fin is sufficiently circulated so that the efficiency of heat radiation from the radiation fin is increased. Therefore, it is more preferable not to form a structure for sealing the laser element such as a cap and to provide an air-cooling fan to blow air to the laser chip to forcibly circulate the air. Furthermore, in order to concentrate and guide the wind generated by the air-cooling fan to the laser chip, it is provided with a plurality of air guide plates that are arranged so as to spread from the laser chip toward the air-cooling fan.
It is more preferable because the heat radiation efficiency is further improved.

FIG. 3 is a perspective view showing a gallium nitride-based compound semiconductor laser chip according to the first embodiment of the present invention. On the substrate 31, In _x Ga _1-x N (0 ≦ x <
The active layer 344 composed of 1) is an n-side Al _y Ga _1-y N
(0 ≦ y <1) layer 33 and p-side Al _z Ga _1-z N (0
≦ z <1) It is sandwiched by the layer 35, and a so-called double hetero structure is formed.

The structure of the gallium nitride-based compound semiconductor laser chip shown in FIG. 3 will be described below with reference to FIG. Although GaN is preferably used as the substrate 31, a different substrate different from the gallium nitride-based compound semiconductor may be used. As the heterogeneous substrate, for example, C
Surface, R surface, or A surface having sapphire as a main surface, spinel (an insulating substrate such as MgA1 ₂ O ₄ , Si,
C (including 6H, 4H, 3C), ZnS, ZnO, Ga
It is possible to grow a nitride semiconductor, such as an oxide substrate that lattice-matches As, Si, and a gallium nitride-based compound semiconductor, and it has been known in the past, and a substrate material different from the nitride semiconductor can be used. Examples of preferable different substrates include sapphire and spinel. The heterogeneous substrate may be off-angled, and in this case, it is preferable to use a step-shaped off-angled substrate because the underlayer made of gallium nitride grows with good crystallinity. Furthermore,
When a heterogeneous substrate is used, after growing a gallium nitride-based compound semiconductor as an underlayer before forming an element structure on the heterogeneous substrate, the heterogeneous substrate is removed by a method such as polishing to remove the gallium nitride-based compound semiconductor. The element structure may be formed as a single substrate, or a different substrate may be removed after the element structure is formed.

When a heterogeneous substrate is used, when a device structure is formed through a buffer layer (low temperature growth layer) 32 and an underlayer (not shown) made of a gallium nitride-based compound semiconductor (preferably GaN), nitriding is performed. The growth of the gallium compound semiconductor is improved. In addition, as a base layer (growth substrate) provided on a heterogeneous substrate, ELOG (Epitaxi
A growth substrate with good crystallinity can be obtained by using a gallium nitride-based compound semiconductor grown by ally laterally overgrowth. As a specific example of the ELOG growth layer, a mask region formed by growing a gallium nitride-based compound semiconductor layer on a heterogeneous substrate and providing a protective film on the surface of which a growth of a gallium nitride-based compound semiconductor is difficult, By providing the non-mask region for growing the gallium nitride-based compound semiconductor in a stripe shape and growing the nitride semiconductor from the non-mask region, the growth in the lateral direction is performed in addition to the growth in the film thickness direction. As a result, the mask region also has a layer formed by growing a gallium nitride-based compound semiconductor. In another form, the gallium nitride-based compound semiconductor layer grown on a heterogeneous substrate may be provided with an opening, and the film may be grown by lateral growth from the side surface of the opening.

On the substrate 31, the n-side contact layer 331 forming the n-side gallium nitride compound semiconductor layer 33, the crack prevention layer (not shown), the n-side cladding layer 332, and the buffer layer 32 are provided. n-side light guide layer 33
3 is formed. The layers other than the n-side clad layer 332 may be omitted depending on the device. The n-side nitride semiconductor layer needs to have a bandgap wider than that of the active layer at least in a portion in contact with the active layer, and therefore, it is preferable that the composition includes Al. Further, each layer may be grown while being doped with n-type impurities to be n-type, or may be grown undoped to be n-type.

Of the n-side gallium nitride-based compound semiconductor layer 33
An active layer 344 is formed on the top. Active layer 344
Is In_x1Ga_1-x2N well layer (0 <x₁<1) and I
n_{x Two}Ga_1-x2N barrier layer (0 ≦ x_Two<1, x₁>
x_Two) MQ is repeatedly laminated by an appropriate number of times.
It has a W structure, and both ends of the active layer are barrier layers.
Has become. The well layer is formed undoped,
All barrier layers except the final barrier layer are n-type non-doped, such as Si and Sn.
Pure is preferably 1 × 10¹⁷~ 1 x 10¹⁹cm ^-3
It is formed by doping with a concentration of.

On the active layer 344, a p-type electron confinement layer 35 is formed as a p-side gallium nitride compound semiconductor 35.
1, p-side optical guide layer 352, p-side cladding layer 353, p
The side contact layer 354 is formed. The layers other than the p-side cladding layer 353 may be omitted depending on the device. The p-side gallium nitride-based compound semiconductor layer needs to have a wider bandgap than that of the active layer, at least in the portion in contact with the active layer.
A composition containing 1 is preferable. Also, each layer is p
It may be grown to be p-type while being doped with a type impurity, or may be p-type by diffusing p-type impurities from another adjacent layer.

In the p-type nitride semiconductor layer, a ridge stripe is formed up to the middle of the p-side light guide layer 352, and further, the insulator film 40, the p-side electrode 36, the n-side electrode 37, the p-pad electrode 38, and The n-pad electrode 39 is formed to form a gallium nitride-based compound semiconductor laser chip. After the laser chip is die-bonded to the heat sink, the heat sink fin 110 and the metal wire 130 for energization are formed on the pad electrode by the wire bonder to complete the laser according to the present invention. In Figure 1, p
Although the heat radiation fins are formed in two rows on the pad electrode 38 and one row on the n pad electrode 39, the arrangement of the heat radiation fins is not limited to that shown in the drawing. At least one of the heat radiation fins 110 is preferably formed immediately above the ridge stripe. Moreover, the metal wire 130 for electricity supply may be formed on the ridge instead of the radiation fin. It is preferable to enhance the heat dissipation by exposing the laser chip to the air without using a cap that covers the laser chip.

[Second Embodiment] FIG. 5 shows the first embodiment.
Is a gallium nitride-based compound semiconductor laser formed by partially replacing the heat radiation fin 110 of the throw-away type with the heat radiation fin 120 of a loop type. Since the loop type heat radiation fin 120 can also radiate heat to the metal electrode terminal 22, the heat radiation efficiency per fin is higher than that of the discarding type heat radiation fin 110. Similar to the conducting metal wire 130, the loop-type heat dissipation fin 120 is formed by being bonded to the pad electrode by the first bond and being bonded to the electrode terminal 22 of the stem by the second bond and then being cut.
Since the loop-type radiating fin 120 also functions as a current-carrying metal wire, it cannot be distinguished from the current-carrying metal wire especially when it is formed of the same metal wire as the current-carrying metal wire. Therefore, in FIG. 5, the same gold wire is used, and the metal wires for energization are not particularly distinguished, and all of them are loop type heat radiation fins 120.
It has been described as. However, it is possible to make a distinction between the loop-type heat radiation fin and the current-carrying metal wire by changing the material and thickness of the metal wire used.

Although the loop type heat radiation fin 120 has a high heat radiation efficiency, the number of heat radiation fins that can be bonded is limited because the area of the electrode terminal 22 is limited. Further, if all of the loop type heat radiation fins 120 are used, the loops may be entangled with each other and peeled off from the laser chip. Therefore, as shown in FIG. 5, the loop type heat radiation fins 120 and the discarding type heat radiation fins 110 may be formed in a mixed manner. Of course, all the radiation fins may be formed as a loop type by devising such as increasing the area of the electrode terminal 22 and appropriately changing the length of the loop so as not to be entangled.

[Third Embodiment] FIGS. 6 and 7 are schematic views of a gallium nitride-based compound semiconductor laser according to a third embodiment. 7A and 7B, except that the p-pad electrode 38 is formed as shown in FIG.

In the first and second embodiments, since the p pad electrode having a constant thickness is formed along the convex shape of the ridge portion, the surface of the p pad electrode has a convex portion. When the radiation fin is formed by wire bonding, good adhesion can be achieved only on a flat surface having no large step, so that the radiation fin cannot be formed on the step portion. Therefore, as shown in FIG. 6, it is preferable to increase the thickness of the p pad electrode other than the ridge portion to form the p pad electrode surface flat. That is,
When the gallium nitride-based compound semiconductor laser has a ridge stripe structure, it is preferable that the p pad electrode 38 is formed so as to cover the steps of the ridge stripe structure and have a substantially flat surface. With the p-pad electrode formed in this way, it is possible to densely form the heat-dissipating fins 110 of a discarding type as shown in FIG. 7, for example. The radiation fins may be arranged other than those shown in FIG. 7 and may be of a loop type.

[Fourth Embodiment] The fourth embodiment is formed in the same manner as the first to third embodiments, except that the n pad electrode and the p pad electrode have different shapes. Since heat from the active region is more easily conducted to the p-pad electrode than to the n-pad electrode, increasing the area of the p-pad electrode to increase the number of heat-dissipating fins that can be bonded improves the efficiency of heat dissipation as a whole. FIG. 8 shows an example of a mode in which the p pad electrode is widened. The n-pad electrode is large enough to bond at least the current-carrying metal wire 130. The position where the n pad electrode is formed is not limited to the corner portion as shown in FIG. 8, and may be formed anywhere. However, when the n pad electrode is formed on the element side portion near the electrode terminal 22, a metal wire for conduction is formed. It is preferable because it is easy to do.

[0044]

Example 1 A substrate 31 made of sapphire (C-face) is set in a reaction vessel, the inside of the vessel is sufficiently replaced with hydrogen, and then the temperature of the substrate is kept at 1050 ° C. while flowing hydrogen.
And clean the substrate. The substrate 31 includes sapphire C plane, sapphire having R plane and A plane as main surfaces, an insulating substrate such as spinel (MgA1 2 O4), SiC (including 6H, 4H, 3C), Z
A semiconductor substrate made of nS, ZnO, GaAs, GaN or the like can be used. When an insulating substrate is used, the p electrode and the n electrode are taken out from the same surface side, but in the case of a conductive substrate, the n electrode can be formed from the back surface side of the substrate.
However, a conductive substrate may be used or a structure in which positive and negative electrodes are taken out on the same surface side.

(Buffer layer 32) Subsequently, the temperature is changed to 510.
C., hydrogen was used as a carrier gas, and ammonia and TMG (trimethylgallium) were used as source gases.
A buffer layer 32 made of GaN is grown on top of it to a film thickness of about 200Å. The buffer layer 32 is AlN, GaN, Al
GaN, etc., at a temperature of 900 ° C. or less, 0.1 μm or less,
Preferably, it can be formed by several dozen Å to several hundred Å. This buffer layer is formed in order to mitigate the lattice constant irregularity between the substrate and the nitride semiconductor, but it may be omitted depending on the growth method of the nitride semiconductor, the type of the substrate, and the like.

(N-side contact layer 331) Buffer layer 3
After the growth of 2, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reached 1050 ° C., n-type Ga doped with Si at 1 × 10 ¹⁹ / cm ³ was also used, using TMG, ammonia gas as the source gas, and silane gas as the impurity gas.
An n-side contact layer 331 made of N is grown to a film thickness of 6 μm. The n-side contact layer 331 is an n-type In _x Al.
_y Ga _1-x-y N (0 ≦ x, 0 ≦ y, x + y ≦ 1), and its composition is not particularly limited, but preferably n-type GaN and Al having a y value of 0.1 or less. _x Ga _1-x N
Then, it is easy to obtain a good ohmic contact with the n-electrode 37.

(Crack prevention layer) Next, the temperature is set to 800.degree.
Then, TMG, TMI (trimethylindium), ammonia, and silane gas are used as source gases, and Si is 1 × 1.
A crack prevention layer made of In _0.10 Ga _0.90 N doped with 0 ¹⁹ / cm ³ is grown to a film thickness of 500 Å.
The crack prevention layer is an n-type nitride semiconductor containing In,
The growth of InGaN preferably prevents cracks from forming in the nitride semiconductor layer containing Al. This crack prevention layer is 100 Å or more,
It is preferable to grow the film with a thickness of 0.5 μm or less. 1
If it is thinner than 00Å, it is difficult to act as a crack preventive as described above, and if it is thicker than 0.5 μm, the crystal itself tends to turn black. The crack prevention layer may be omitted depending on the conditions such as the growth method and the growth apparatus.

(N-side clad layer 332) Next, the temperature is raised to 10
The temperature is set to 50 ° C., TMA (trimethylaluminum), TMG, NH ₃ , and SiH ₄ are used as a source gas, and Si is 1 ×.
10 ¹⁹ / cm ³ doped n-type Al _0.20 Ga
The first layer of _0.80 N has 20Å and Si has 1 × 10
The second layer of n-type GaN doped with ¹⁹ / cm ³
To grow 0Å. And grow this pair 125 times,
An n-side cladding layer 332 made of a multilayer film having a total film thickness of 0.5 μm (5000 Å) is grown. This n-side clad layer 3
32 acts as a carrier confinement layer and a light confinement layer, and is a nitride semiconductor containing Al, preferably AlGa.
A first layer containing N or GaN or InGaN, and a second layer made of a nitride semiconductor having a composition different from that of the first layer.
It is desirable to grow a multi-layer film having a layered structure with the above layers. As described above, when a superlattice structure is formed by stacking and growing nitride semiconductor layers having different compositions of 100 Å or less, more preferably 70 Å or less, and most preferably 50 Å or less, a single nitride semiconductor layer The film thickness becomes less than the critical limit film thickness, the crystallinity becomes very good, and continuous oscillation easily occurs at room temperature. The superlattice layer as the cladding layer is present in at least one of the n-side gallium nitride compound semiconductor layer or the p-type nitride semiconductor layer outside the active layer, and preferably in both layers. Desirable to be present. The total film thickness of the n-side cladding layer 332 is 100 Å or more and 2 μm or less, more preferably 500 Å
As described above, it is desirable to grow it at a thickness of 1 μm or less.

(N-side light guide layer 333) Subsequently, 105
N-type GaN doped with Si at 1 × 10 ¹⁹ / cm ³ at 0 ° C.
The n-side light guide layer 333 is grown to a thickness of 0.2 μm. This n-side light guide layer 333 acts as a light guide layer of an active layer, and it is desirable to grow GaN and InGaN, and it is desirable to grow it to a film thickness of usually 100 Å to 5 μm, more preferably 200 Å to 1 μm. As described above, in the present invention, n
The side gallium nitride-based compound semiconductor layer 33 also includes a layer formed of multiple layers of n-side gallium nitride-based compound semiconductor layers (331 to 333). A buffer layer 32 may be interposed between the substrate and the n-side gallium nitride compound semiconductor layer as in this embodiment.

(Active layer 34) Next, the source gas is TMG,
The active layer 34 is formed by using TMI, ammonia, and silane gas.
Grow. The active layer 34 maintains the temperature at 800 ° C.,
First, Si is 8 × 10 ¹⁸/cm^ThreeIn doped with
_0.20Ga_0.80The well layer made of N has a film thickness of 25 Å
Grow with. Then just change the molar ratio of TMI
8 × 10 Si at the same temperature¹⁸/cm^ThreeDoped In
_0.05Ga_0.95The barrier layer made of N has a film thickness of 50Å
Grow with. This operation is repeated twice, and finally the well layer
To have a multiple quantum well structure. Dope the active layer
Impurities that do not enter the well layer and the barrier layer as in this example.
Or one of them may be doped. Note that
Doping with n-type impurities tends to lower the threshold value.

(P-side electron confinement layer 351) Next, the temperature is raised to 1050 ° C., and TMG, TMA, ammonia, C
p ₂ Mg (cyclopentadienyl magnesium) is used, and the band gap energy is larger than that of the active layer.
P-type Al _0.10 doped with Mg at 1 × 10 ²⁰ / cm ³
Ga _{0 . The} p-side electron confinement layer 351 made of ₉₀ N
Grow with a film thickness of 00Å. This p-side electron confinement layer 3
51 is p-type, but since it has a small film thickness, it may be i-type in which carriers are compensated by doping n-type impurities, and most preferably p-type. The thickness of the p-side electron confinement layer 351 is 0.1 μm or less, more preferably 500 Å or less,
Most preferably, it is adjusted to 300Å or less. When grown to a thickness greater than 0.1 μm, the p-side electron confinement layer 351
This is because cracks are likely to occur inside, and a nitride semiconductor layer with good crystallinity is difficult to grow. Also, carriers cannot pass through this energy barrier due to the tunnel effect. If the AlGaN having a larger Al composition ratio is formed thinner, the laser element is likely to oscillate. For example, Y value is 0.2
For the above Al _y Ga _1-y N, it is desirable to adjust it to 500 Å or less. The lower limit of the film thickness of the p-side electron confinement layer 351 is not particularly limited, but it is desirable to form the p-side electron confinement layer 351 with a film thickness of 10 Å or more.

(P-side light guide layer 352) Then, 105
At 0 ° C., the p-side optical guide layer 352 made of Mg-doped p-type GaN having a bandgap energy smaller than that of the cap layer doped with Mg at 1 × 10 ²⁰ / cm ³ is 0.2 μm.
To grow. This p-side light guide layer 352 is n
Similar to the side light guide layer 333, it is desirable to act as a light guide layer of an active layer and grow GaN and InGaN. Usually, the film thickness is 0.01 μm or more and 5 μm or less, more preferably 0.02 μm or more and 1 μm or less. It is desirable to grow in.

(P-side clad layer 353) Then 1050
P-type Al doped with Mg at 1 × 10 ²⁰ / cm ³ at ℃
The first layer of _0.20 Ga _0.80 N is 20Å,
A second layer of n-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown by 20Å. And this pair 12
It is grown five times to grow a p-side clad layer 353 made of a multilayer film having a total film thickness of 0.5 μm (5000 Å). This p
Like the n-side cladding layer 332, the side-cladding layer 353 also acts as a carrier confinement layer and an optical confinement layer, and has a first layer made of AlGaN, GaN, or InGaN, and a nitride having a composition different from that of the first layer. It is desirable to grow a multilayer film layer having a laminated structure with a second layer made of a semiconductor. When the clad layer has a superlattice structure as described above, the film thickness of the single nitride semiconductor layer becomes equal to or less than the critical limit film thickness, crystallinity becomes very good, and continuous oscillation is easily performed at room temperature. It is also very effective as a light confinement layer for confining the light emission of the active layer. The total film thickness of the p-side cladding layer 353 is 0.01 μm or more and 2 μm.
Hereafter, it is desirable to grow at a thickness of 0.05 μm or more and 1 μm or less.

In the case of a semiconductor device having a double hetero structure having an active layer having a quantum well layer as in the present embodiment, the film thickness having a band gap energy larger than that of the active layer 34 is in contact with the active layer 34. A cap layer made of a nitride semiconductor having a thickness of 0.1 μm or less, preferably a p-side electron confinement layer 351 made of a nitride semiconductor containing Al, is provided.
A p-side light guide layer 352 having a bandgap energy smaller than that of the p-side electron confinement layer 351 is provided at a position farther from the active layer than the p-side electron confinement layer 351. A p-side cladding layer 35 containing a gallium nitride-based compound semiconductor having a band gap larger than that of the p-side light guide layer 352, preferably a gallium nitride-based compound semiconductor containing Al.
Providing 3 is highly preferred. Moreover, since the thickness of the p-side electron confinement layer 351 is set as thin as 0.1 μm or less, it does not act as a carrier barrier,
The holes injected from the p-layer can pass through the p-side electron confinement layer 351 due to the tunnel effect, are efficiently recombined in the active layer, and the laser output is improved. That is, the injected carriers are the p-side electron confinement layer 351.
Has a large band gap energy, the carriers do not overflow in the active layer and are blocked by the p-side electron confinement layer 351 even if the temperature of the semiconductor element rises or the injection current density increases. It can be stored in the active layer and can efficiently emit light.

(P-side contact layer 354) Finally, p-side
On the clad layer 353, Mg was added at 1 × 10 at 1050 ° C.
²⁰/cm ^ThreeP-side contact made of doped p-type GaN
Layer 354 is grown to a film thickness of 150Å. p side contour
Layer 354 is p-type In_xAl_yGa_1-x-yN (0
≦ x, 0 ≦ y, x + y ≦ 1)
More preferably, Mg-doped GaN or Mg-doped
Al with a Y value of 0.1 or less_yGa_1-yIf N,
The most preferable ohmic contact with the p-electrode 36 is obtained.
The thickness of the p-side contact layer 354 is 500 Å or less,
Preferably less than 300Å, most preferably less than 200Å
It is desirable to adjust to.

After completion of the reaction, the temperature is lowered to room temperature, and the wafer is further heated in a nitrogen atmosphere in a reaction vessel at 700 ° C.
Annealing is performed at 0 ° C. to reduce the resistance of the layer formed of the p-type gallium nitride compound semiconductor.

After the annealing, the wafer is taken out of the reaction container and etched by the RIE apparatus to etch the uppermost p-side contact layer 354 and the p-side clad layer 353 as shown in FIG. A ridge stripe having a width is formed. When forming the ridge stripe, it is designed so that the center of the stripe width is close to the n electrode 37 to be formed later. In the case of forming a ridge stripe, by making the layer above the p-side gallium nitride-based compound semiconductor layer containing Al, which is above the active layer, into a ridge shape, the light emission of the active layer is concentrated under the ridge, It is easy to unify the modes and the threshold value tends to decrease.

Next, a mask is formed on the surface of the ridge stripe and the exposed surface of the p-side cladding layer 353,
Similarly, etching is performed by RIE, and as shown in FIG.
The surface of the n-side contact layer 331 on which the electrode 37 is to be formed is exposed. After the surface is exposed, Ni and Au are formed on the entire upper surface of the ridge stripe of the p-side contact layer 354 which is the uppermost layer.
The p-electrode 36 is formed. Note that examples of the material of the p-electrode 36 that can obtain a preferable ohmic contact with the p-side contact layer 354 include Ni, Pd, Ag, Ni / Au, and the like. On the other hand, the n-electrode 37 made of Ti and Al is formed in parallel with the ridge stripe on the n-side contact layer 331 exposed earlier. Materials for the n-side contact layer 331 and the n-electrode 37 that can obtain a preferable ohmic property include Al, Ti, W, Cu, Zn, Sn, and In.
Metals or alloys such as

Next, an insulator film 40 made of SiO ₂ is formed on the entire surface of the nitride semiconductor layer except the positions where the p electrode 36 and the n electrode 37 are formed. After forming the insulator film 40, A
A p pad electrode 38 made of u is formed on the p electrode 36 and the insulator film 40 by being electrically connected to the p electrode 36. Similarly, the n pad electrode 39 made of Au is
On the n-electrode 37 and the insulator film 40, the n-electrode 37
It is formed by being electrically connected to. The ratio of the area of the p-pad electrode 38 to the surface area of the n-pad electrode is about 2: 1.
The surface of the p-pad electrode 38 thus formed is shown in FIG.
Also, as shown in FIG. 4, there is a step due to the shape of the ridge. The broken line a in FIG. 1 indicates the position of the step.

As described above, the n-electrode 37 and the p-electrode 3
The wafer on which No. 6 is formed is transferred to a polishing apparatus, and the substrate 31 on the side on which the nitride semiconductor is not formed is lapped by using a diamond abrasive to make the thickness of the substrate 100 μm. After lapping, the substrate surface is mirror-finished by polishing with 1 μm with a finer polishing agent.

After polishing the substrate, scribe the polishing surface side,
Cleavage is performed in a bar shape in a direction perpendicular to the ridge stripe, and a resonator having a resonator length of 500 μm is manufactured on the cleavage plane. A dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface,
Finally, the bar is cut in the direction parallel to the ridge stripe to form a laser chip.

Further, the laser chip is fixed face up (the substrate and the heat sink are opposed to each other) to the heat sink, and the respective pad electrodes and the electrode terminals of the stem are bonded by the gold wire 130 for conduction. further,
The diameter of the adhesive portion 111 is about 70 μm, and the fin tip portion 112
A plurality of heat radiation fins 110 having a length of 100 μm are bonded onto the n pad electrode 39 and the p pad electrode 38 by wire bonding. At this time, the radiating fins 110 are not formed on the steps on the side of the ridge. Further, a cap for protecting the laser chip is not provided in order to enhance the effect of heat dissipation.

When the oscillation of the laser thus formed was tried, the threshold current density was 3 kA / c at room temperature.
At m ² and a threshold voltage of 4 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and a lifetime of 12,000 hours or more was shown.

[Embodiment 2] As shown in FIG. 5, it is formed in the same manner as in Embodiment 1 except that half of the discarding type heat radiation fins 110 of the first embodiment are replaced with loop type heat radiation fins 120. To do. When the oscillation of the laser according to the present invention thus formed was tried, continuous oscillation of an oscillation wavelength of 405 nm was confirmed at room temperature with a threshold current density of 3 kA / cm ² and a threshold voltage of 4 V, and a lifetime of 14,000 hours or more. showed that.

Example 3 As shown in FIGS. 6 and 7,
The p-pad electrode 38 formed in Examples 1 and 2 is formed so that its surface is flat. At this time, the p-pad electrode immediately above the ridge is formed with a thickness of 0.8 μm. If the surface of the p-pad electrode 38 is flat, the heat radiation fins can be densely formed to increase the number. Figure 7
This is an example of the arrangement pattern of the radiation fins when they are densely formed, and other arrangements may be used. In addition, a part or all of the abandonment type radiation fin 110 in FIG.
A loop type heat radiation fin 120 may be used. When an attempt was made to oscillate the laser thus formed, at room temperature, the threshold current density was 3 kA / cm ² , the threshold voltage was 4 V, and
Continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and 15,000
It has a life span of more than an hour.

[Comparative Example] A comparative laser formed in the same manner as in Example 1 was formed as a comparative example except that the radiation fins were not formed. When I tried to oscillate this laser,
At room temperature, a threshold current density of 3 kA / cm ² and a threshold voltage of 4 V were observed, and continuous oscillation with an oscillation wavelength of 405 nm was confirmed.
It showed a life of 0000 hours or more.

The gallium nitride-based compound semiconductor laser according to the present invention is provided with a radiation fin having a high radiation performance on the electrode of the laser, so that it can be used for a long time, at a high output and for a long time. Further, the heat dissipation fin of the present invention has an advantage that it can be formed at the time of wire bonding of the current-carrying metal wire and can be formed in a short time and at low cost.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

FIG. 2 is an example of a radiation fin of the present invention.

FIG. 3 is a perspective view showing an embodiment of the present invention.

FIG. 4 is a sectional view showing an embodiment of the present invention.

FIG. 5 is a schematic diagram showing an embodiment of the present invention.

FIG. 6 is a sectional view showing an embodiment of the present invention.

FIG. 7 is a schematic diagram showing an embodiment of the present invention.

FIG. 8 is a schematic view showing an embodiment of the present invention.

[Explanation of symbols]

1 ... Laser 2 ... Stem 3 ... Laser chip 21 ... Heat sink 22 ... Electrode terminal 23 ... Stem support rod 31 ... substrate 32 ... Buffer layer 33 ... N-side gallium nitride-based compound semiconductor layer 34 ... Active layer 35 ... P-side gallium nitride compound semiconductor layer 36 ... p electrode 37 ... n electrode 38 ... p pad electrode 39 ... n pad electrode 40 ... Insulator film 110 ... Discard type heat dissipation fin 111 ... Fin bonded part 112 ... fin tip 120 ... Loop type heat radiation fin 130 ... Metal wire for electricity 331 ... n-side contact layer 332 ... N-side clad layer 333: n-side light guide layer 351 ... p-side electron confinement layer 352 ... P-side light guide layer 353 ... P-side clad layer 354 ... P-side contact layer a ... step of p pad electrode

Claims (9)

[Claims] 1. A gallium nitride-based compound semiconductor laser in which a plurality of gallium nitride-based compound semiconductor layers are stacked on a substrate and bipolar pad electrodes are formed on the gallium nitride-based compound semiconductor layer side. A gallium nitride compound semiconductor laser characterized in that at least one metal wire for heat radiation is bonded to at least one of the pad electrodes in addition to the metal wire intended for energization. . 2. The gallium nitride-based compound semiconductor laser according to claim 1, wherein the heat radiation metal wire is bonded by wire bonding. 3. The gallium nitride-based compound semiconductor laser according to claim 1, wherein the heat radiation metal wire is a gold wire. 4. At least one of the heat dissipation metal wires
The gallium nitride-based compound semiconductor laser according to any one of claims 1 to 3, wherein the book is bonded directly on the active region. 5. The gallium nitride based compound semiconductor laser according to claim 4, wherein the thickness of the pad electrode to which the heat radiation metal wire is adhered is 0.5 μm or more. 6. The gallium nitride-based compound semiconductor laser has a ridge stripe structure, and the pad electrode is formed so as to cover a step of the ridge stripe structure and have a substantially flat surface. The gallium nitride-based compound semiconductor laser according to any one of claims 1 to 5. 7. The gallium nitride according to claim 1, wherein one end of the heat radiation metal wire is adhered to the pad electrode and the other end is adhered to the stem electrode. -Based compound semiconductor laser. 8. The gallium nitride-based compound semiconductor laser according to claim 1, wherein a total area of both electrodes of the pad electrode is 80% or more of a chip area. 9. The gallium nitride-based material according to claim 1, wherein an area of the pad electrode formed on the p-side semiconductor is 60% or more of a chip area. Compound semiconductor laser.