JP3484842B2 - Nitride semiconductor laser device - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to a nitride semiconductor (In _X A
1 _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1), and a method for manufacturing a resonator of the laser device.

[0002]

2. Description of the Related Art In _x Al _y Ga has been used as a material for a short wavelength semiconductor laser device having an emission wavelength of 550 nm or less.
_A nitride semiconductor composed of _1-XY N (0 ≦ X, 0 ≦ Y, X + Y ≦ 1) is known. Up to now, a light emitting diode (LED) has been realized in a nitride semiconductor, but a report that it oscillates in a laser diode (LD) has not been made yet.

LEDs made of nitride semiconductors are basically
On the sapphire substrate, an n-type clad layer made of n-type AlGaN, an active layer made of InGaN, and p-type AlGa
It has a double hetero structure in which a p-type cladding layer made of N is laminated.

[0004]

The realization of the double hetero structure made of a nitride semiconductor realizes the basic structure of the LD. When the structure of the LD is completed, for laser oscillation, an optical resonator corresponding to a parallel mirror provided in the device is required to resonate the light emission of the active layer in the device. For example, GaAs, InGaAl
In the case of an infrared or red semiconductor laser made of a cleavable semiconductor material such as P, a GaAs substrate having the same cleavability as the substrate.
Is used, the cleavage property of GaAs is used to
It is common practice to use the cleavage plane as a resonator.

However, since the nitride semiconductor is laminated on sapphire, which is an insulative insulating substrate, there is a problem that it is difficult to form a resonator of the LD. Even if the wafer is forcibly broken and the split surface is used as a cleavage plane, it hardly becomes a resonator, and in reality, oscillation is not achieved.

Therefore, the present invention has been made in view of the above circumstances, and an object thereof is to obtain a nitride semiconductor from a wafer in which a nitride semiconductor is laminated on a substrate so as to have an LD structure. Another object of the present invention is to provide a method for manufacturing a resonator of a physical semiconductor to realize a laser element capable of lasing.

[0007]

A nitride semiconductor laser device according to the present invention is a nitride semiconductor laser device in which a nitride semiconductor is laminated on a substrate, and a facing end face of the nitride semiconductor serves as a resonator. Is made of spinel, and the resonator is a cut surface obtained by cutting the nitride semiconductor wafer laminated on the spinel substrate, and the cut surface is polished.
It has a smoother surface, and the resonator surface has TiO2, A
a small amount selected from the group consisting of 12O3, Si, and SiOx.
It is characterized in that a dielectric multilayer film made of at least one is formed. The unevenness of the nitride semiconductor layer on the cavity surface is 50 angstroms or less.

Furthermore, the method of manufacturing a resonator for a laser device according to the present invention is characterized in that after a nitride semiconductor is laminated on a spinel substrate, the substrate is cut and the cut surface is used as a resonator. . In the device and method of the present invention,
Needless to say, the cut surface referred to in the claims refers to the cut surface obtained by cutting the chip by cutting means such as a dicer or a laser, and partially scratches the wafer by scribing or the like and breaks the wafer from the scratch. The cut surface cut by the means is also included.

Spinel used in the present invention means Mg and Al.
Which is a co-oxide of MgAl ₂ O ₄ and has a crystal plane of spinel (111) for growing a nitride semiconductor.
The surface is a preferable crystal growth surface.

To grow a nitride semiconductor, for example, metal organic chemical vapor deposition (MOVPE), molecular beam vapor phase epitaxy (MBE), gas source molecular beam vapor phase epitaxy (MOMB).
E), a vapor deposition method such as a halide vapor deposition method (HDVPE) can be used. A laser device can be manufactured by growing a nitride semiconductor using these growth methods.

The structure of the laser element is preferably a double hetero structure in which the active layer is sandwiched between the n-type and p-type cladding layers as described above, and particularly preferably the active layer is a single quantum well, or A high-power laser device can be realized by using a quantum well structure such as a multiple quantum well structure.

As a structure of a laser device using InGaN as an active layer, for example, n-GaN (contact layer) / n-
AlGaN / n-InGaN or n-GaN / InG
aN active layer / p-AlGaN or p-GaN / p-A
lGaN / p-GaN (contact layer) or n-
GaN / n-AlGaN / InGaN active layer / p-Al
GaN / p-GaN or n-AlGaN / n-A
lGaN / n-InGaN / InGaN active layer / p-A
lGaN / p-GaN or n-GaN / InGa
N active layer / p-AlGaN / p-GaN, or n-
AlGaN / InGaN active layer / p-GaN / p-Al
A structure such as GaN / p-GaN may be mentioned. The composition of the n and p clad layers can be changed by designing so that the difference in refractive index from the active layer becomes large according to the emission wavelength of the active layer, that is, the composition of the active layer. InGa with quantum well structure
The N active layer has a well layer thickness of 70 Å or less,
It is desirable that the thickness of the barrier layer be 150 angstroms or less. In the case of the single quantum well structure, if the thickness of the well layer is thicker than 70 Å, it tends to be difficult to obtain a device having a high output. In case of multiple quantum well structure, well +
When the total thickness of the combination of barrier + well + barrier + well layer is 500 angstroms or less, a device with high output can be obtained.

[0013]

In the method of the present invention, the substrate on which the nitride semiconductor is grown is the spinel. Since spinel has a softer crystal than sapphire, it has the advantage of being easy to process. Moreover, when a nitride semiconductor is grown,
The crystallinity of the nitride semiconductor is almost the same as that grown on the sapphire substrate, or there is a tendency that a semiconductor layer having better crystallinity can be obtained. Therefore, the possibility of oscillation when used as a laser element is higher than that of sapphire.

Further, the sapphire substrate is very hard and it is almost impossible to cut it into chips by using a dicer. However, since the spinel substrate is soft as described above, it can be easily cut by a dicer. . In addition, cracking, chipping, etc. of the nitride semiconductor layer generated on the cut surface during dicing are extremely reduced. Furthermore, after scribing the side of the substrate on which the nitride semiconductor has not been grown, the cut surface obtained by dividing the substrate by the scribe line also has a cleavage property because the spinel has cleavability. The occurrence rate of defects such as is extremely reduced, which is very convenient for manufacturing a resonator.

Further, in the method of the present invention, by polishing both cut surfaces of the spinel substrate, the cut surfaces become closer to a mirror surface and closer to a parallel mirror, and oscillation becomes easier. On the other hand, it is very difficult to obtain a smooth surface even if sapphire is polished. This is because sapphire is very hard. In order to form a parallel mirror which becomes a resonator by the method of the present invention, there are etching means such as dry etching and wet etching in addition to polishing, but in the case of a nitride semiconductor,
Due to factors such as the selection of mask material and the type of etching gas, it is difficult to obtain smooth end faces that are parallel to each other and have few irregularities by etching. In the present invention, polishing of spinel succeeded in producing a resonance surface which becomes a parallel mirror.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The method of the present invention will be described below with reference to the drawings. 1 is a perspective view showing the shape of a laser device obtained by the method of the present invention, and FIG. 2 is a schematic sectional view showing the structure of the laser device of FIG. These elements are electrode stripe type laser elements.

On a 2-inch φ single crystal spinel substrate 1 in which the (111) plane of spinel (MgAl ₂ O ₄ ) is exposed,
Using a MOVPE reactor, the n-type contact layer 2 made of Si-doped n-type GaN was 4 μm, and Si-doped n-type A was used.
0.5 μ of n-type clad layer 3 made of 0.4 Ga0.6 N
m, an n-type optical guide layer 4 made of Si-doped In0.05Ga0.95N 0.2 μm, an active layer 5 made of non-doped In0.2Ga0.8N having a single quantum well structure with a film thickness of 30 Å, Mg-doped p-type The p-type optical guide layer 6 made of Al0.05Ga0.95N is 0.2 μm, and the Mg-doped p-type A
0.5 μ of p-type clad layer 7 made of 0.4 Ga0.6 N
m, grow in order.

Next, the wafer is taken out of the apparatus, and a protective film made of SiO _{2 in} a stripe shape having a width of 5 μm is grown on the surface of the p-type cladding layer 7 by using a photolithography technique. This protective film serves as a protective film for selectively growing the nitride semiconductor, and after removing the protective film, current can be concentrated in the active layer.

Next, the wafer on which the protective film is formed is placed again in the reactor, and the surface of the p-type clad layer 7 as described above is made of n-type GaN made of Si-doped n-type GaN via the protective film.
The type current blocking layer 8 is grown. This n-type GaN layer grows on the surface of the p-type cladding layer 7, but does not grow on the surface of the protective film described above.

After the bulb constricting layer 8 is grown, the wafer is taken out of the reaction vessel and the SiO ₂ protective film is dissolved and removed with hydrofluoric acid. After that, the wafer is placed in a reaction vessel, and finally, a p-type contact layer 9 made of Mg-doped p-type GaN is grown to 0.5 μm on the bulb confinement layer 8.

Next, after taking out the wafer from the reaction container, a protective film is formed again on the surface of the p-type contact layer 9, and the nitride semiconductor layer is etched by an etching apparatus until the n-type contact layer 2 is exposed. . The n-type contact layer 2 exposed by etching becomes the surface on which the negative electrode should be formed, and the p-type GaN layer from which the protective film was removed becomes the surface on which the positive electrode should be formed. Further, a positive electrode containing Ni and Au is formed on almost the entire surface of the p-type contact layer 9, and a striped negative electrode containing Ti and Al is formed on the surface of the n-type contact layer 2. In the method of the present invention, it is desirable to manufacture an electrode stripe type laser device, and a cut surface orthogonal to the stripe electrode is used as a resonator.

As described above, the wafer on which the positive and negative electrodes are formed on the same side is set on the scriber, and the substrate surface on which the nitride semiconductor is not formed is arranged at a pitch of 500 μm in the direction orthogonal to the stripe electrodes. Scribe. The plane that divides the wafer in this direction becomes the resonator. The wafer is pushed down by the rollers to obtain a bar (ber) with an exposed resonance surface. The nitride semiconductor layer on the resonator surface of the cut chip was scarcely cracked or cracked, the unevenness was 100 angstroms or less, and the defect rate from the 2-inch φ substrate was 5% or less.

Next, the nitride semiconductor bar, the resonance surface of which is exposed by cutting, is inserted into a polishing jig, and the resonance surface is mirror-polished with alumina slurry. The surface opposite to the polished surface is also polished in the same manner, and the cut surfaces facing each other are used as parallel mirrors to manufacture a resonator. By this polishing, the unevenness of the cavity surface is reduced to 50 angstroms or less.

The polished semiconductor bar is removed from the jig and transferred to a sputtering device, where TiO ₂ , A
A dielectric multilayer film made of l ₂ O ₃ is formed. The dielectric multilayer film The other Si, materials such as SiO _X can be used.
Since these materials have little absorption in the ultraviolet and blue regions and have a large difference in refractive index between the materials, they are suitable for blue lasers using nitride semiconductors and dielectric multilayer films formed on the cavity surface of ultraviolet laser devices. There is.

Next, along the n-electrode pitch of the bar having the dielectric multilayer film formed on the resonance surface, the substrate is cut into chips with a dicer to form a laser element of 350 μm × 500 μm. FIG. 2 is a sectional view showing the structure of the element after cutting,
FIG. 1 is a perspective view showing the shape of the element shown in FIG.

When the nitride semiconductor laser device manufactured as described above was placed on a heat sink and a current was passed between the electrodes, laser oscillation with a current density of 700 mA / cm ² and an oscillation output of 5 mW and a wavelength of 450 nm was observed.

[Embodiment 2] The wafer is cut in the same manner as in Embodiment 1 except that a dicer is used when cutting the wafer into bars. It should be noted that, although no chipping or cracking of the nitride semiconductor was observed on the resonance surface due to dicing, the unevenness was 100 angstroms or more. These irregularities are reduced to 50 angstroms or less by the subsequent polishing, and when used as a laser device, the current density is 70 as in the device of Example 1.
The same oscillation was shown at 0 mA / cm ² .

[Embodiment 3] When a nitride semiconductor layer is grown in Embodiment 1, the active layer 5 is made to have the following multiple quantum well structure. First, as a well layer, In0.2Ga0.8
N 20 angstrom, then In0.05 as a barrier layer
Ga 0.0.95N layer 70 Å, then well layer +
An active layer having a total film thickness of 200 Å having a five-layer structure such as a barrier layer and a well layer. After that, when a laser element was manufactured in the same manner as in Example 1, the current density was 70%.
The oscillation output was 6 mW at 0 mA / cm ² , and oscillation at a wavelength of 440 nm was exhibited.

[0029]

As described above, according to the present invention, it is possible to obtain a laser chip with almost no unevenness, chipping or cracks on the cavity surface. Therefore, a nitride semiconductor device which exhibits laser oscillation for the first time in the short wavelength region. Can be realized. Since the short wavelength laser element can dramatically increase the capacity as a light source for writing and reading, its industrial utility value is very large.

[Brief description of drawings]

FIG. 1 is a perspective view showing the shape of a laser element according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view showing the structure of the laser device shown in FIG.

[Explanation of symbols]

1 ... Spinel substrate 2 ... N-type contact layer 3 ... N-type cladding layer 4 ... N-type optical guide layer 5 ... Active layer 6 ... P-type optical guide layer 7 ... P-type cladding layer 8 ... N-type current blocking layer 9 ... P-type contact layer

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-152072 (JP, A) JP-A-49-53388 (JP, A) Proceedings of 42nd Symposium on Applied Physics, Spring 1995, 1995, 28p-ZH-12 Proceedings of the 1995 Tokai Branch Union Conference of the Institute of Electrical Engineers of Japan, 1995, p. 149 Appl. Phys. Lett. 1995, 67 [17], p. 2521-2523 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01S 5/00-5/50 H01L 33/00

Claims (2)

(57) [Claims] 1. A nitride semiconductor laser device in which a nitride semiconductor is laminated on a substrate, and the opposing nitride semiconductor end faces serve as resonators, wherein the substrate is made of spinel, and the resonator is laminated on a spinel substrate. The cut nitride semiconductor wafer is a cut surface, and the cut surface is polished to be a smooth surface.
And the resonator surface has TiO2, Al2O3, Si,
The material is at least one selected from the group consisting of SiOx
A nitride semiconductor laser device having a dielectric multilayer film formed thereon. 2. The nitride semiconductor laser device according to claim 1, wherein the unevenness of the nitride semiconductor layer on the cavity facet is 50 angstroms or less.