JP3456413B2 - Method for growing nitride semiconductor and nitride semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a nitride semiconductor (In _X Al _Y Ga) having a small number of crystal defects that can be used as a substrate.
_1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1) growth method, light emitting diode (LED), laser diode (LD),
The present invention relates to a nitride semiconductor element used for a light emitting element such as a solar cell and an optical sensor, a light receiving element, or an electronic device such as a transistor and a power device.

[0002]

2. Description of the Related Art Nitride semiconductors, which are known as materials for blue LEDs and pure green LEDs, are grown on a sapphire substrate in a lattice mismatched state. It is known that when a semiconductor material is grown in a lattice mismatch, crystal defects are generated in the semiconductor and the crystal defects have a great influence on the life of the semiconductor device. In the case of a nitride semiconductor, there are very many threading dislocations as crystal defects. However, in the case of a nitride semiconductor LED element, although its threading dislocations are large, for example, 10 ¹⁰ / cm ² or more, its life is hardly affected. This indicates that the nitride semiconductor is very resistant to deterioration unlike other semiconductor materials.

On the other hand, in the nitride semiconductor laser device, LE
It is grown on a sapphire substrate similarly to D, but if a nitride semiconductor that has an element structure is laminated on sapphire via a buffer layer like LED, the crystal defect is the same as that of LED. However, in the case of a laser device, L
Since the current density is 1 to 2 orders of magnitude higher than that of the ED, crystal defects tend to directly affect the lifetime unlike the LED.
In a device such as a laser element that concentrates a current in an extremely small area, it is very important to reduce crystal defects in the semiconductor.

Therefore, attempts have recently been made to grow a nitride semiconductor having a small number of crystal defects such as a nitride semiconductor substrate on a substrate made of a material different from the nitride semiconductor such as sapphire. (For example, Proceedings of The Second International Confer
ence on Nitride Semiconductors-ICNS'97 Proceedings, Octo
ber 27-31, 1997, P492-493, also ICNS'97 Proceedings, Octo
ber 27-31, 1997, P500-501). In these techniques, a conventional GaN layer with a large number of crystal defects is thinly grown on a sapphire substrate, a protective film made of SiO ₂ is partially formed on the GaN layer, and a halide vapor phase is formed on the protective film. Growth method (H
VPE), metalorganic vapor phase epitaxy (MOVPE) and other vapor phase epitaxy methods to grow the GaN layer laterally again. This method grows the nitride semiconductor laterally on the protective film, and is therefore generally called lateral over growth (LOG).

Further, we have manufactured a nitride semiconductor laser device including an active layer on a nitride semiconductor substrate manufactured by LOG, and achieved the world's first continuous oscillation of 10,000 hours or more at room temperature. Published (ICNS'97 Proceedings, Octob
er 27-31, 1997, P444-446).

[0006]

According to the conventional method for growing a nitride semiconductor, the number of crystal defects is certainly smaller than that of a nitride semiconductor grown directly on a foreign substrate. This is because the crystal defects can be partially concentrated by LOG. According to this method, crystal defects can be concentrated on the upper portion of the protective film, and a region having few crystal defects can be formed in the window portion. That is, crystal defects can be intentionally unevenly distributed.

However, in the conventional growth method, the number of crystal defects appearing on the surface of the nitride semiconductor is still large and it is not yet sufficiently satisfactory. Further, also in the nitride semiconductor device, the crystal defects are unevenly distributed, and therefore the reliability cannot be said to be sufficient. Therefore, even if many laser elements are manufactured from one wafer, only a few ones having a satisfactory life can be obtained. In order to manufacture a device having a long life, it is necessary to further reduce the number of crystal defects appearing on the surface of the nitride semiconductor. Therefore, the present invention has been made in view of such circumstances, and an object of the present invention is to provide a method for growing a nitride semiconductor with few crystal defects that can serve as a substrate, and mainly to improve reliability. An object is to provide an excellent nitride semiconductor device.

[0008]

A method of growing a nitride semiconductor according to the present invention comprises: a first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from that of the nitride semiconductor;
Of the nitride semiconductor layer, which is partially formed on the surface of the nitride semiconductor layer, and a protective film having a property that the nitride semiconductor is unlikely to grow on the surface is heated, and a nitrogen source gas and 3 A method for growing a nitride semiconductor substrate, wherein a continuous second nitride semiconductor layer is grown on the protective film and the underlayer by simultaneously supplying a group source gas, and nitrogen for the group 3 source gas is used. It is characterized in that the molar ratio of the source gas (nitrogen source / group 3 source: hereinafter referred to as V / III ratio) is adjusted to 2000 or less. The preferred molar ratio is 180
It is adjusted to 0 or less, more preferably 1500 or less. The lower limit is not particularly limited as long as it is a stoichiometric ratio or more, but is preferably 10 or more, more preferably 30 or more,
Most preferably, it is adjusted to 50 or more. In the present invention,
Nitrogen source gas corresponds to hydride gas such as ammonia and hydrazine, and Ga source gas is TMG (trimethylgallium), TEG in the case of metalorganic vapor phase epitaxy.
An organic Ga gas such as (triethylgallium), a hydrogen halide gas that reacts with a group III source such as HCl, or a gallium halide (especially GaCl ₃ ) that reacts with a hydrogen halide gas as a Ga source gas in HVPE. Equivalent to.

The nitride semiconductor device of the present invention is a first semiconductor device grown on a heterogeneous substrate made of a material different from that of the nitride semiconductor.
Of a nitride semiconductor layer and a protective film which is partially formed on the first nitride semiconductor layer and has a property that a nitride semiconductor does not easily grow on the surface of the nitride semiconductor layer. A second nitride semiconductor layer having a region with many crystal defects on the side closer to it and a region with fewer crystal defects on the side distant from the underlayer, and an active layer on the second nitride semiconductor layer. It is characterized in that a plurality of nitride semiconductor layers containing is grown.

When the underlying layer is left to form the device structure, the thickness of the second nitride semiconductor layer is 1 μm or more to 5 μm or more.
It is characterized by being in the range of 0 μm or less. The thickness of the second nitride semiconductor layer is preferably adjusted to 3 μm to 40 μm, more preferably 5 μm to 20 μm. The underlayer has a different substrate having a lattice constant and a thermal expansion coefficient different from those of the nitride semiconductor. Therefore, the nitride semiconductor grown on the underlayer is always strained. This distortion warps the wafer after growth or breaks the nitride semiconductor substrate. Therefore, by adjusting the thickness of the nitride semiconductor substrate within the above range, it is possible to reduce the warp of the wafer and reduce the cracking of the second nitride semiconductor layer. Further, when the thickness of the second nitride semiconductor layer is thinner than 1 μm, the second nitride semiconductor layer does not grow sufficiently on the protective film, crystal defects are still many, and a layer serving as a substrate is formed. Hateful.

When the underlying layer is left to form the device structure, an n-side contact layer made of a nitride semiconductor grown on the second nitride semiconductor layer and doped with an n-type impurity has an n-electrode. It is characterized by being formed. Si and Ge are preferably used as the n-type impurities. If this second nitride semiconductor layer is made of undoped GaN to improve the crystallinity, the resistivity will be high, and therefore a nitride semiconductor doped with an n-type impurity thereon, preferably Si-doped GaN.
When the layer is used as a contact layer, dislocations due to crystal defects are reduced and a highly reliable device can be obtained.

When the underlying layer is left and the device structure is formed, the n-electrode is formed on the second nitride semiconductor layer on the side of the region having many crystal defects. Among nitride semiconductors, those with many crystal defects tend to have a higher carrier concentration than those with few crystal defects. Therefore,
A region having many crystal defects in the second nitride semiconductor layer is naturally n.
The threshold voltage and Vf (forward voltage) tend to decrease if the n electrode is provided on the n + side.

The method for growing a nitride semiconductor device according to the present invention comprises:
A first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from that of the nitride semiconductor, and partially formed on the surface of the first nitride semiconductor layer, and the nitride semiconductor grows on the surface. A base layer composed of a protective film having a difficult property is heated, and a nitrogen source gas and a Group 3 source gas are simultaneously supplied to the surface of the base layer to form a gas on the protective film and the base layer.
An area with many crystal defects on the side close to the continuous underlayer,
It has a region with few crystal defects on the side distant from the underlayer.
A method for growing a nitride semiconductor device comprising a second nitride semiconductor layer, and a plurality of nitride semiconductor layers including an active layer grown on the second nitride semiconductor layer, comprising: After growing the layer, a ridge stripe is formed on the protective film.
At the position p, which is the surface layer of the nitride semiconductor layer.
Forming a p-electrode on the side contact layer, and thereafter removing the base layer composed of the heterogeneous substrate and the first nitride semiconductor layer and the protective film, and then exposing the exposed second nitride semiconductor layer . And forming a counter electrode structure by forming an n electrode on the surface of the region having many crystal defects . The method for growing a nitride semiconductor device includes the step of doping an n-type impurity in the second nitride semiconductor layer. A method for growing a nitride semiconductor device, wherein the molar ratio of the nitrogen source gas to the Group 3 source gas (nitrogen source /
It is characterized in that the group 3 source) is adjusted to 2000 or less.
Has regions with few crystal defects and regions with many crystal defects
Active on the region of the second nitride semiconductor layer having few crystal defects.
Formed by growing a plurality of nitride semiconductor layers including a conductive layer
In the semiconductor device , the nitride semiconductor layer has a ridge
P, which has a tripe and is a surface layer of the nitride semiconductor layer
Forming a p-electrode on the side contact layer,
The conductor layer is the second nitride semiconductor on the region side with few crystal defects.
The number of crystal defects appearing on the surface of the layer is determined by observing the cross-section TEM.
1 × 10 ⁶ pieces / cm ² or less, a region with many crystal defects
An n-electrode was formed on the surface of the second nitride semiconductor layer on the side
A counter electrode structure is formed. The thickness of the second nitride semiconductor layer is 30 μm or more. A nitride semiconductor device in which the second nitride semiconductor layer is doped with an n-type impurity. A nitride semiconductor device in which the n-type impurities are Si and Ge. The p electrode is Ni, Pt, Pd, Co, Ni / A
A nitride semiconductor device selected from the group consisting of u, Pt / Au, and Pd / Au. The n-electrode is made of Al, Ti, W, Cu,
At least one selected from the group consisting of Zn, Sn, and In
A nitride semiconductor device which is a metal or an alloy having two.
The nitride semiconductor device, wherein the second nitride semiconductor layer is grown by the method according to claim 1. Further, when the underlying layer is removed to form an element structure, the thickness of the second nitride semiconductor layer is preferably 50 μm or more. This is because when the film thickness is 50 μm or more, the number of regions with few crystal defects is further increased, and when a nitride semiconductor containing an active layer is grown thereon, a device structure with very few crystal defects can be formed.

Further, when the underlayer is removed, the n-electrode is formed on the second nitride semiconductor layer in the region having many crystal defects. The underlayer is, for example, etched,
It can be separated from the nitride semiconductor substrate by a technique such as polishing. The back surface of the second nitride semiconductor layer from which the underlayer has been removed is exposed. However, when an n-electrode and a p-electrode are provided to form the final device, the n-electrode is formed on the entire back surface to activate the active layer. The p-electrode provided on the side of the nitride semiconductor layer including the layer and the n-electrode face each other. Since the second nitride semiconductor layer has the low carrier concentration region having the same composition and few crystal defects and the high carrier concentration region having many crystal defects, by providing the n-electrode in this high carrier concentration region, An efficient element can be manufactured.

Although the second nitride semiconductor layer is basically in an undoped state, it tends to have a minimum number of crystal defects, a high mobility, and a low carrier concentration. It may be grown by doping with an n-type impurity in order to increase the height. In particular, when the underlayer is removed and an electrode is formed on the surface of the second nitride semiconductor layer, the second nitride semiconductor layer is doped with an n-type impurity such as Si or Ge to reduce the carrier concentration. , For example, 1 × 10 ¹⁷ /
It is desirable to adjust ^{cm 3 ~5 × 10 19 / cm} 3.

It is most preferable that the second nitride semiconductor layer of the device of the present invention is grown by the growth method of claim 1 or 2, but in the device of the present invention, the second nitride semiconductor layer is formed. If the region with many crystal defects and the region with few crystal defects are in substantially the same direction with respect to the nitride semiconductor stacking direction,
The growing method is not particularly limited.

[0017]

1 to 4 are schematic cross-sectional views showing the crystal structure of a second nitride semiconductor layer according to the growth method of the present invention, while FIGS. 5 to 7 are nitrogen source gas. FIG. 8 is a schematic cross-sectional view showing a crystal structure of a nitride semiconductor layer by a conventional growth method in which the supply amount of Al is small. In these figures,
1, 1'are different substrates made of sapphire, 2, 2 '
Is a first nitride semiconductor layer grown on a heterogeneous substrate and having crystal defects substantially uniform in the layer, and 3 and 3'are protective films made of, for example, SiO ₂ having a property that the nitride semiconductor is hard to grow on the surface. Reference numerals 4, 4'indicate second nitride semiconductor layers which will be substrates. Hereinafter, the operation of the method for growing a nitride semiconductor of the present invention will be described based on these drawings while comparing it with a conventional method. The thin lines shown in FIGS. 1 to 7 schematically show the crystal defects of the nitride semiconductor.

The first nitride semiconductor layer 2 grown on the heterogeneous substrate 1 has crystal defects substantially uniformly in the layer. Then, the protective film 3 is partially (for example, stripe-shaped) formed on the surface of the first nitride semiconductor layer 2. The base layer having the heterogeneous substrate 1, the first nitride semiconductor layer 2, and the protective film 3 is heated to, for example, 900 ° C. to 1100 ° C., and a continuous second nitriding process is performed on the surface of the base layer to form a substrate. The object semiconductor layer 4 is grown.

In the method of the present invention, the molar ratio of the nitrogen source gas to the Group 3 source gas (V / III ratio) is adjusted to 2000 or less. By reducing the V / III ratio in this manner, the second nitride semiconductor 4 grown from the window portion (portion where the protective film is not formed) as shown in FIG.
Grows in a substantially vertical direction, or in a shape close to an inverted trapezoid. The crystal defects occurring in the first nitride semiconductor layer 2 also extend to the second nitride semiconductor layer 4, but when the second nitride semiconductor 4 is grown in a substantially vertical direction, As shown in FIG. 1, crystal defects tend to extend in the lateral direction (end face direction) in the upper portion of the protective film. In this figure, the area of the protective film and the area of the window are almost the same, but in the growth method of the present invention, the crystal area is smaller when the area of the protective film is larger than the area of the window. A second nitride semiconductor layer is obtained.

When the growth is further continued, the nitride semiconductor grows on the protective film 3 not only in the upward direction but also in the lateral direction (LOG). According to the method of the present invention, the end face of the second nitride semiconductor 4 grows almost perpendicular to the horizontal plane of the different substrate, so that the second nitride semiconductor 4 is close to the protective film as shown in FIG. The side away from the protective film tends to be connected earlier than the side, or the end faces tend to be connected almost at the same time. What is important here is that the crystal defects occurring in the second nitride semiconductor layer are extended in the lateral direction and are therefore unlikely to appear on the surface of the second nitride semiconductor layer.

When the growth is further continued, the second nitride semiconductor layer 4 grows upward as well. However, as shown in FIG.
Or grows downward. Then, according to the growth, the crystal defects of the second nitride semiconductor layer 4 tend to grow in the direction of the protective film 3 or to spread laterally.

Therefore, the grown second nitride semiconductor layer 4
4 is that the crystal defects of the second nitride semiconductor layer extend only in the lateral direction in accordance with the growth direction of the second nitride semiconductor as shown in FIG. 4 and are not connected to the surface to form threading dislocations. , Very few appear on the surface. In some cases, when growing thicker, crystal defects may stop during growth. Therefore, as the second nitride semiconductor layer grows thicker on the underlayer, crystal defects tend to decrease. For example, the second nitride semiconductor layer may have a thickness of 30 μm.
When grown at a thickness of m or more, a second nitride semiconductor layer having very few crystal defects appearing on the surface can be obtained, and a particularly realistic G
Acts as an aN substrate.

By thus growing the second nitride semiconductor, the second nitride having a region with many crystal defects on the side closer to the underlayer and a region with fewer crystal defects on the side farther from the underlayer. The object semiconductor layer can be grown. According to the growth method of the present invention, for example, the number of crystal defects appearing on the surface can be 1 × 10 ⁸ pieces / cm ² or less, further 1 × 10 ⁶ pieces / cm ² or less when observed by a cross-section TEM. .

On the other hand, in the conventional growth method with a V / III ratio of more than 2000 shown in FIGS. 5 to 7, the second nitride semiconductor layer 4 grown from the window portion as shown in FIG. 'Grow in a triangular shape (roof shape) in its window. When the second nitride semiconductor layer 4 ′ grows in a triangular shape, the crystal defects extending from the first nitride semiconductor layer 2 ′ to the second nitride semiconductor layer 4 ′ have a triangular side portion (roof portion). ).

When the growth is further continued, the second nitride semiconductor layer 4 ′ grows laterally and is first connected to the surface of the protective film which is the base of the triangle. If you continue to grow,
The crystal defects toward the roof also grow upward.

Therefore, as shown in FIG. 7, the crystal defects of the second nitride semiconductor layer 4'by the conventional growth method are connected at the upper portion of the protective film and form threading dislocations on the surface of the second nitride semiconductor layer. appear. Therefore, regions having many crystal defects and regions having few crystal defects are unevenly distributed on the surface of the second nitride semiconductor layer.

In the growth method of the present invention, in order to grow the second nitride semiconductor vertically or in an inverted trapezoidal shape with respect to the substrate, the molar ratio of the nitrogen source gas and the Group 3 source gas is adjusted. Is very important and the ratio (nitrogen source /
When the group 3 source) is more than 2000, the second nitride semiconductor grows in a triangular shape as in the conventional case, so that it tends to be difficult to obtain the second nitride semiconductor layer having few crystal defects.

[0028]

[Embodiment 1] FIG. 8 is a schematic perspective view showing a shape of a laser device according to an embodiment of the present invention, showing a cross section of the laser device taken in a direction perpendicular to a ridge stripe. There is. Hereinafter, Embodiment 1 will be described with reference to this drawing.

A heterogeneous substrate 1 made of sapphire having a 2-inch φ and C-plane as a main surface is set in a MOVPE reaction vessel, the temperature is set to 500 ° C., hydrogen is used as a carrier gas and TMG (trimethylgallium (Ga (CH ₃ ) ₃ : T
MG) and ammonia (NH ₃ ) are used to grow a buffer layer (not shown) made of GaN with a film thickness of 200 Å. After growing the buffer layer, the temperature is raised to 1050.
C., and the first nitride semiconductor layer 2 also made of GaN is grown to a film thickness of 5 .mu.m. The first nitride semiconductor layer 2 has an Al mixed crystal ratio X value of 0.5 or less, Al _X Ga _1-X N (0
It is desirable to grow ≦ X ≦ 0.5). If it exceeds 0.5, cracks are likely to occur in the crystal itself rather than crystal defects, so that crystal growth itself tends to be difficult. Further, it is desirable that the film thickness is made thicker than that of the buffer layer and adjusted to 10 μm or less. In addition to sapphire, a substrate made of a material different from a nitride semiconductor, such as SiC, ZnO, spinel, or GaAs, which is known for growing a nitride semiconductor, can be used.

After the growth of the first nitride semiconductor layer 2, the wafer is taken out of the reaction container, and the first nitride semiconductor layer 2 is removed.
A stripe-shaped photomask is formed on the surface of the
A protective film 3 made of SiO _{2 having a} stripe width of 10 μm and a stripe interval (window portion) of 2 μm is formed with a thickness of 1 μm by a D device. The shape of the protective film is a stripe shape,
It may have any shape such as a dot shape or a grid shape, but when the area of the protective film is larger than that of the window portion, the second nitride semiconductor layer 3 having less crystal defects grows easily. Examples of the material for the protective film include oxides and nitrides such as silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide (TiO _x ), zirconium oxide (ZrO _x ), and multilayer films of these. Besides, a metal or the like having a melting point of 1200 ° C. or higher can be used. These protective film materials withstand the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C., and have the property that the nitride semiconductor does not grow on the surface or hardly grows.

(Second nitride semiconductor layer 4) After forming the protective film 3, the wafer is set again in the MOVPE reaction vessel, the temperature is set to 1050 ° C., and ammonia is added at 0.27 mol.
l / min, TMG 225 μmol / min (V / III ratio = 12
00), the second nitride semiconductor layer 4 made of undoped GaN is grown to a film thickness of 30 μm. After the growth, when observing the second nitride semiconductor layer with a cross-section TEM, the number of crystal defects is large (10 ⁸ / cm ² or more) in the region up to about 5 μm from the interface of the first nitride semiconductor layer. In the region above 5 μm, there were few crystal defects (10 ⁶ / cm ² or less), and it could be sufficiently used as a nitride semiconductor substrate. On the surface after growth, almost no crystal defects are observed in the upper part of the protective film, and crystal defects tend to appear in the upper part of the window part (stripe center part). Of more than 2000), the number of crystal defects is smaller by two digits or more.

The second nitride semiconductor layer can be grown by the halide vapor phase epitaxy method (HVPE), but can also be grown by the MOVPE method as described above.
It is most preferable to grow GaN that does not contain In or Al in the second nitride semiconductor layer. As a gas at the time of growth, triethyl gallium (Ga (C
Most preferably, an organic gallium compound such as ₂ H ₅ ) ₃ : TEG) is used, and ammonia or hydrazine is used as the nitrogen source. In addition, Si is added to the second nitride semiconductor layer.
The carrier concentration may be adjusted to an appropriate range by doping an n-type impurity such as Ge. In particular, when removing the heterogeneous substrate, the first nitride semiconductor layer, and the protective film, it is desirable to dope the second nitride semiconductor layer with an n-type impurity.

(N-side buffer layer 11 = also serving as n-side contact layer) Next, using ammonia and TMG and silane gas as an impurity gas, Si is deposited on the second nitride semiconductor layer 4 by 3 layers.
The n-side buffer layer 11 made of GaN doped with × 10 ¹⁸ / cm ³ is grown to a film thickness of 5 μm. This buffer layer is n in the case of manufacturing a light emitting device having a structure as shown in FIG.
It also acts as a contact layer for forming electrodes.
In addition, when the heterogeneous substrate and the protective film are removed and an electrode is provided on the second nitride semiconductor layer, it can be omitted. This n-side buffer layer is a buffer layer grown at a high temperature, and is formed on a substrate made of a material different from a nitride semiconductor, such as sapphire, SiC, and spinel, and 900
At low temperature below ℃, GaN, AlN, etc.
It is distinguished from a buffer layer which is directly grown with a film thickness of m or less.

(Crack Prevention Layer 12) Next, TMG, T
A crack prevention layer 12 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm by using MI (trimethylindium) and ammonia at a temperature of 800 ° C. The crack prevention layer is a nitride semiconductor containing at least indium, preferably In _X Ga _{1 -X} N (0 <X <0.5) grown to a thickness of 0.5 μm or less to thereby grow Al. It is possible to prevent cracks from entering the nitride semiconductor containing.

(N-side clad layer 13 = superlattice layer) Next, n-type A doped with Si at 1 × 10 ¹⁹ / cm ³ at 1050 ° C. using TMA, TMG, ammonia and silane gas.
A first layer of _0.2 Ga _0.8 N is grown to a thickness of 25 angstroms, then silane gas and TMA are stopped, and a second layer of undoped GaN is grown to a thickness of 25 angstroms. Then, a superlattice layer is formed in the following manner: first layer + second layer + first layer + second layer + ... And an n-side cladding layer 12 made of a superlattice having a total film thickness of 0.8 μm is grown. When a superlattice in which nitride semiconductors having different bandgap energies are stacked is manufactured, if one of the layers is heavily doped with impurities and so-called modulation doping is performed, the threshold value tends to decrease.

(N-side optical guide layer 14) Subsequently, the silane gas is stopped and the n-side optical guide layer 14 made of undoped GaN is grown to a thickness of 0.1 μm at 1050 ° C. This n-side light guide layer acts as a light guide layer for the active layer,
It is desirable to grow GaN or InGaN, usually 100 angstrom to 5 μm, and more preferably 2
It is desirable to grow the film with a film thickness of 00 angstrom to 1 μm. This layer can also be an undoped superlattice layer. In the case of forming a superlattice layer, the bandgap energy of the nitride semiconductor layer having a larger bandgap energy forming the superlattice is larger than that of the well layer of the active layer and is larger than that of Al _0.2 Ga _0.8 N of the n-side cladding layer. Make it smaller.

(Active layer 15) Next, the active layer 14 is grown using TMG, TMI, and ammonia. The temperature of the active layer is kept at 800 ° C., and a well layer made of undoped In _0.2 Ga _0.8 N is grown to have a film thickness of 40 Å. Next, a barrier layer made of undoped In _0.05 Ga _0.95 N is formed at 1 temperature at the same temperature only by changing the molar ratio of TMI.
It is grown to a film thickness of 00 angstrom. A well layer and a barrier layer are sequentially stacked, and finally the barrier layer is formed, and the total film thickness is 4
A 40 Å multiple quantum well structure (MQW) active layer is grown. The active layer may be undoped as in this embodiment, or may be doped with n-type impurities and / or p-type impurities. The impurities may be doped in both the well layer and the barrier layer, or may be doped in either one.

(P-side cap layer 16) Next, the temperature is raised to 10
Raise to 50 ℃, TMG, TMA, ammonia, Cp2M
g (cyclopentadienyl magnesium), which has a bandgap energy larger than that of the p-side optical guide layer 17 and is p-type Al _0.3 Ga doped with 1 × 10 ²⁰ / cm ^{3 of} Mg.
_A p-side cap layer 16 made of _0.7 N is grown to a film thickness of 300 angstrom. By forming the p-type cap layer 16 with a film thickness of 0.1 μm or less, the output of the device tends to be improved. The lower limit of the film thickness is not particularly limited, but it is desirable to form the film with a film thickness of 10 angstroms or more.

(P-side light guide layer 17) Subsequently, Cp2M
g, TMA is stopped, and at 1050 ° C., a p-side optical guide layer 17 made of undoped GaN having a bandgap energy smaller than that of the p-side cap layer 16 is grown to a film thickness of 0.1 μm. This layer acts as a light guide layer for the active layer, and is similar to the n-type light guide layer 14 in GaN and InGaN.
It is desirable to grow in. The p-side light guide layer may be a superlattice layer made of an undoped nitride semiconductor or a p-type impurity-doped nitride semiconductor. When the superlattice layer is used, the bandgap energy of the nitride semiconductor layer having the larger bandgap energy is preferably larger than that of the well layer of the active layer and smaller than that of Al _0.2 Ga _0.8 N of the p-side cladding layer. .

(P-side clad layer 18) Subsequently, 1050
P-type Al _0.2 Ga doped with Mg at 1 × 10 ²⁰ / cm ^{3 at} ℃
_A third layer of _0.8 N is grown to a thickness of 25 Å, and then only TMA is stopped and undoped Ga is added.
A fourth layer made of N is grown to a film thickness of 25 Å, and a p-side clad layer 18 made of a superlattice layer having a total film thickness of 0.8 μm is grown. This layer is also the n-side cladding layer 13
When a superlattice in which nitride semiconductors having different bandgap energies are stacked is produced, if one of the layers is heavily doped with impurities and so-called modulation doping is performed, the threshold value tends to decrease.

(P-side contact layer 19) Finally, 105
Mg was added to the p-side cladding layer 18 at 0 ° C. in an amount of 2 × 10 ²⁰
/ Cm ³ -doped p-type GaN p-side contact layer 18 is grown to a thickness of 150 Å. p
The side contact layer 19 is a p-type In _X Al _Y Ga _1-XY N
(0 ≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, the p-electrode 21
And the most preferable ohmic contact is obtained. Also p-type A
Since the nitride semiconductor having a small bandgap energy is used as a p-side contact layer in contact with the p-side clad layer 17 having a superlattice structure containing l _Y Ga _{1 -Y} N, the film thickness is reduced to 500 angstroms or less. In addition, the carrier concentration of the p-side contact layer 18 is substantially increased, a preferable ohmic contact with the p-electrode is obtained, and the threshold current and voltage of the device are reduced.

The wafer on which the nitride semiconductor has been grown as described above is placed in a reaction vessel in a nitrogen atmosphere at 700
Annealing is performed at 0 ° C. to further reduce the resistance of the p-type impurity-doped layer.

After annealing, the wafer is taken out of the reaction container, and the uppermost p-side contact layer 18 and the p-side cladding layer 17 are etched by a RIE apparatus to have a stripe width of 4 μm as shown in FIG. It has a ridge shape. What is important is that when forming a ridge stripe, the ridge stripe position is set to a position avoiding the central portion of the stripe-shaped window portion where crystal defects tend to appear a little as shown in FIG. When the stripes are formed at positions where there are almost no crystal defects, the crystal defects tend not to extend to the active layer, so that the device can have a long life and reliability is improved.

Next, a mask is formed on the ridge surface and RIE is performed.
Etching is performed to expose the surface of the n-side buffer layer 11. The exposed n-side buffer layer 11 also functions as a contact layer for forming the n-electrode 23.
Although the n-side buffer layer 11 is used as the contact layer in FIG. 8, etching is performed up to the region of the second nitride semiconductor layer 4 having many crystal defects, and the second nitride semiconductor layer 4 is used as the contact layer. You can also

Next, p electrodes 20 made of Ni and Au are formed in stripes on the ridge outermost surface of the p-side contact layer 19. Examples of the material of the p-electrode 20 that can obtain a preferable ohmic contact with the p-side contact layer include Ni, Pt, and P.
Examples thereof include d, Co, Ni / Au, Pt / Au, and Pd / Au.

On the other hand, the n-electrode 22 made of Ti and Al is formed in a stripe shape on the surface of the n-side buffer layer 11 exposed previously. As a material of the n-side buffer layer 11 or the n-electrode 22 that can obtain a preferable ohmic property with the GaN substrate 10, a metal or alloy such as Al, Ti, W, Cu, Zn, Sn, or In is preferable.

Next, as shown in FIG.
Si is formed on the surface of the nitride semiconductor layer exposed between the electrodes 22.
An insulating film 23 made of O ₂ is formed, and a p pad electrode 21 electrically connected to the p electrode 20 through the insulating film 23 is formed. The p-pad electrode 21 is substantially the p-electrode 21.
The surface area of the p-electrode and wire bonding on the p-electrode side,
Allows die bonding.

As described above, the wafer on which the n-electrode and the p-electrode are formed is transferred to the polishing apparatus, and the sapphire substrate on the side on which the nitride semiconductor is not formed is lapped by using the diamond abrasive to sapphire. The thickness of the substrate is 70
μm. After lapping, 1μ with finer abrasive
m polishing is performed to make the surface of the substrate a mirror surface, and the entire surface is metallized with Au / Sn.

Then, scribe the Au / Sn side,
Cleavage is performed in a bar shape in a direction perpendicular to the striped electrode, and a resonator is formed on the cleaved surface. SiO ₂ and TiO ₂ on the cavity surface
Then, a bar was cut in the direction parallel to the p-electrode to form a laser chip. Next, when the chip was placed face up (the substrate and the heat sink faced each other) on the heat sink, each electrode was wire-bonded, and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.0 kA / It was confirmed that continuous oscillation with an oscillation wavelength of 405 nm was obtained at a cm ² and a threshold voltage of 4.0 V, and the life was 10,000 hours or more. Further, when 500 laser elements were randomly extracted from the same wafer and the life of the laser elements was measured, 70% or more showed a life of 10,000 hours or more.

[Comparative Example] In Example 1, when the second nitride semiconductor layer 4 was grown, ammonia was added at 0.36 mol.
l / min, TMG 162 μmol / min (V / III ratio = 22
As 22), a second nitride semiconductor layer 4 made of undoped GaN was grown to a film thickness of 30 μm and a ridge stripe was formed at an arbitrary position. It was 5% or less that achieved 10,000 hours or more.

Example 2 A laser device was manufactured in the same manner as in Example 1 except that the thickness of the second nitride semiconductor was 10 μm when growing the second nitride semiconductor. The number of crystal defects appearing on the surface of No. 1 tends to be larger by one digit than that in Example 1, and 50% of 500 have a life of 10,000 hours or more.

[Embodiment 3] FIG. 9 is a schematic sectional view showing the structure of a laser device according to another embodiment of the present invention.
The same reference numerals denote the same parts. The second embodiment will be described below with reference to this drawing.

Second nitride semiconductor layer 4 in Example 1
Ammonia is added at 0.27 mol / min and T
MG was set to 150 μmol / min (V / III ratio = 1800), and silane gas was further added to grow a second nitride semiconductor layer made of Si-doped GaN with a thickness of 30 μm. The region up to about 5 μm from the interface between the second nitride semiconductor layer 4 and the first nitride semiconductor layer 2 has a large number of crystal defects, and the region above 5 μm has few crystal defects (10 ⁷ / cm ² or less), which was sufficiently usable as a nitride semiconductor substrate.

After that, a nitride semiconductor including an active layer is laminated in the same manner as in Example 1, and then, as shown in FIG. 9, about 6 μm is removed by etching from above the second nitride semiconductor layer. Then, the surface of the second nitride semiconductor layer 4 in the region having many crystal defects is exposed, and n is formed on the surface.
The electrode 22 is formed to be a laser element. This laser element also continuously oscillated at a low threshold value as in Example 1, and 50% or more of the 500 laser elements achieved a life of 10,000 hours or more.

[Example 4] In Example 1, when the second nitride semiconductor layer 4 was grown, ammonia was added at 0.2%.
7 mol / min, TMG 180 μmol / min (V / III ratio =
1500), a laser device was manufactured in the same manner as in Example 1. As a result, continuous oscillation was similarly performed at a low threshold value, and a laser device was obtained in a number substantially equal to that in Example 1.

[Embodiment 5] In Embodiment 1, except that the V / III ratio is set to 800 by increasing the flow rate of only TMG when growing the second nitride semiconductor layer 4. When a laser device was manufactured in the same manner as in 1., continuous oscillation was similarly performed at a low threshold value, and a laser device was obtained in a number substantially equal to that in Example 1.

[Embodiment 6] In Embodiment 1, when the second nitride semiconductor layer 4 is grown, 0.1% ammonia is added.
5 mol / min, TMG 5 mmol / min (V / III ratio = 30)
Other than the above, a laser device was manufactured in the same manner as in Example 1. As a result, 30% or more of the 500 laser devices continuously oscillated at a low threshold and showed a life of 10,000 hours or more.

[Embodiment 7] In Embodiment 1, when the second nitride semiconductor layer 4 is grown, Si is doped to grow the film thickness to 90 μm. Thereafter, in the same manner as in Example 1, a nitride semiconductor layer including an active layer is grown on the second nitride semiconductor layer. When the wafer was taken out from the reaction container after the growth, the wafer was warped like a dish due to the difference in thermal expansion coefficient between sapphire and the second nitride semiconductor layer. Therefore, the foreign substrate side of this wafer is polished to remove the foreign substrate 1, the first nitride semiconductor layer 2, and the protective film 3. By removing the foreign substrate, the wafer can be almost flat.

Next, in the same manner as in Example 1, the p-side clad layer 18 and the upper part thereof are formed into a ridge shape to form a p-electrode 20 and a p-pad electrode 21. However, it is difficult to match the position of the ridge stripe with the window because the protective film is removed. On the other hand, an n-electrode made of Ti / Al is provided on almost the entire surface of the second nitride semiconductor layer on the side where a large number of crystal defects are exposed by removing the protective film, and a laser in a state where the p-electrode and the n-electrode face each other. As an element.

Similarly, this laser element has a low threshold value and continuously oscillates at room temperature, and has a life of 10,000 hours or more.
It was 70% or more in the number.

[0061]

As described above, according to the method for growing a nitride semiconductor of the present invention, it is possible to realize a nitride semiconductor device having very few crystal defects appearing on the surface without concentrating crystal defects at one place. . Therefore, crystal defects can be reduced over the entire second nitride semiconductor layer, so that when a laser element is manufactured, a highly reliable element can be obtained with a higher yield than before. Further, in the device of the present invention, since the nitride semiconductor layer including the active layer is laminated on the second nitride semiconductor layer having few crystal defects appearing on the surface, an extremely reliable device can be realized. .

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing a crystal structure of a nitride semiconductor layer obtained by a growth method of the present invention.

FIG. 2 is a sectional view schematically showing the crystal structure of a nitride semiconductor layer obtained by the growth method of the present invention.

FIG. 3 is a sectional view schematically showing a crystal structure of a nitride semiconductor layer obtained by the growth method of the present invention.

FIG. 4 is a sectional view schematically showing the crystal structure of a nitride semiconductor layer obtained by the growth method of the present invention.

FIG. 5 is a sectional view schematically showing the crystal structure of a nitride semiconductor layer obtained by a conventional growth method.

FIG. 6 is a sectional view schematically showing a crystal structure of a nitride semiconductor layer obtained by a conventional growth method.

FIG. 7 is a sectional view schematically showing a crystal structure of a nitride semiconductor layer obtained by a conventional growth method.

FIG. 8 is a schematic perspective view showing the structure of a laser device according to an embodiment of the present invention.

FIG. 9 is a schematic perspective view showing the structure of a laser device according to another embodiment of the present invention.

[Explanation of symbols]

1 ... Heterogeneous substrate 2 ... First nitride semiconductor layer 3 ... Protective film 4 ... Second nitride semiconductor layer 11 ... n-side buffer layer 12 ... Crack prevention layer 13 ... N-side clad layer 14 ... n-side light guide layer 15 ... Active layer 16 ... p-side cap layer 17 ... p-side light guide layer 18 ... p-side clad layer 19 ... p-side contact layer 20 ... p electrode 21 ... p pad electrode 22 ... n electrode 23 ... Insulating film

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-283799 (JP, A) JP-A-11-145515 (JP, A) JP-A-11-135770 (JP, A) JP-A-10- 312971 (JP, A) JP-A-6-77590 (JP, A) JP-B-6-105797 (JP, B2) JP-A-2001-520169 (JP, A) International Publication 97/011518 (WO, A1) Hideshima Matsushima And 3 others, GaN selective growth to submicron pattern by MOVPE method, IEICE technical report, Japan, Institute of Electronics, Information and Communication Engineers, May 23, 1997, Vol. 97, No. 59, pp. 41-46 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/205 H01L 33/00 H01S 5/30

Claims (10)

(57) [Claims] 1. A first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from that of the nitride semiconductor, and a first nitride semiconductor layer partially formed on the surface of the first nitride semiconductor layer and nitrided on the surface. The underlayer composed of a protective film having a property that a semiconductor does not grow easily is heated, and a nitrogen source gas and a Group 3 source gas are simultaneously supplied to the surface of the underlayer to form the protective film and the underlayer. Crystal defects on the side closer to the continuous underlayer
There are few crystal defects on the side where there are many
A second nitride semiconductor layer having a region,
In the growth method of the nitride semiconductor device having a plurality of nitride semiconductor layer are grown including an active layer on the nitride semiconductor layer, after growing the nitride semiconductor layer, wherein the ridge stripe
A p-electrode is formed at a position on the protective film , a p-side contact layer that is a surface layer of the nitride semiconductor layer is formed, and then a lower layer composed of the heterogeneous substrate, the first nitride semiconductor layer and the protective film is formed. Growth of a nitride semiconductor device including a step of removing a ground layer , and a step of forming an counter electrode structure by forming an n-electrode on the surface of the exposed region of the second nitride semiconductor layer having many crystal defects. Method. 2. The method for growing a nitride semiconductor device according to claim 1, further comprising the step of doping the second nitride semiconductor layer with an n-type impurity. 3. The growth of the nitride semiconductor device according to claim 1, wherein the molar ratio of the nitrogen source gas to the Group 3 source gas (nitrogen source / Group 3 source) is adjusted to 2000 or less. Method. 4. A region having few crystal defects and a crystal defect
Crystal defects of the second nitride semiconductor layer having a large number of regions
A plurality of nitride semiconductor layers including an active layer are formed on the small area.
In a nitride semiconductor device having a long length , the nitride semiconductor layer has a ridge stripe, and
On the p-side contact layer that is the surface layer of the oxide semiconductor layer
And the second nitride semiconductor layer has few crystal defects.
Defects appearing on the surface of the second nitride semiconductor layer on the side of the open region
The number of, 1 × 10 ⁶ cells by the observation of the cross-sectional TEM / cm ² or more
The second nitride semiconductor which is below and has a large number of crystal defects
Forming a counter electrode structure with an n-electrode formed on the surface of the layer
Nitride semiconductor device. 5. The thickness of the second nitride semiconductor layer is 30.
The nitride semiconductor device according to claim 4, wherein the thickness is at least μm. 6. The nitride semiconductor device according to claim 4, wherein the second nitride semiconductor layer is doped with an n-type impurity. 7. The nitride semiconductor device according to claim 6, wherein the n-type impurities are Si and Ge. 8. The p-electrode is made of Ni, Pt, Pd, Co,
The nitride semiconductor device according to claim 4, wherein the nitride semiconductor device is selected from the group consisting of Ni / Au, Pt / Au, and Pd / Au. 9. The n-electrode is made of Al, Ti, W, Cu, Z.
The nitride semiconductor device according to claim 4, which is a metal or an alloy having at least one selected from the group consisting of n, Sn, and In. 10. The second nitride semiconductor layer according to claim 1.
The nitride semiconductor device according to any one of claims 4 to 9, which is grown by the method according to claim 9.