JPH11219910A - Method for growing nitride semiconductor and nitride semiconductor device - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for growing a nitride semiconductor having few crystal defects that can be used as a substrate, and to provide a nitride semiconductor element excellent in reliability. An underlayer consisting of a first nitride semiconductor layer grown on a heterogeneous substrate and a protective film partially formed on the surface of the first nitride semiconductor layer is heated, In the formation, the gas of the nitrogen source and the gas of the group 3 source are mixed in a molar ratio
(Ratio) Adjusted to 2000 or less and grow. The grown nitride semiconductor layer does not become triangular as in the conventional case, but grows in a direction substantially perpendicular to the horizontal plane of the substrate. A nitride semiconductor with few crystal defects can be grown.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention is small nitride semiconductor crystal defects as may be the substrate (In _X Al _Y Ga
_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 or an optical sensor, a light receiving element, or an electronic device such as a transistor or a power device.

[0002]

2. Description of the Related Art A nitride semiconductor known as a material for a blue LED or a pure green LED is grown on a sapphire substrate in a lattice mismatch state. It is known that when a semiconductor material is grown due to lattice mismatch, crystal defects occur in the semiconductor, and the crystal defects greatly affect the life of the semiconductor device. In the case of a nitride semiconductor, there are numerous threading dislocations as crystal defects. However, in the case of the nitride semiconductor LED element, although the threading dislocation is as large as, for example, 10 ¹⁰ / cm ² or more, it hardly affects the life thereof. This indicates that the nitride semiconductor is very resistant to deterioration, unlike other semiconductor materials.

On the other hand, in a nitride semiconductor laser device, LE
Like D, it is grown on a sapphire substrate. However, when a nitride semiconductor having an element structure is stacked on sapphire via a buffer layer like an LED, crystal defects are the same as those of the LED. However, in the case of a laser element, L
Since the current density is one to two orders of magnitude higher than that of the ED, the crystal defect tends to directly affect the lifetime unlike the LED.
In a device such as a laser element that concentrates a current in an extremely small region, it is very important to reduce crystal defects in a semiconductor.

Therefore, attempts to grow a nitride semiconductor having few crystal defects such as a nitride semiconductor substrate on a substrate made of a material different from the nitride semiconductor, such as sapphire, have been actively made recently. (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 having a large number of crystal defects is grown thinly on a sapphire substrate, a protective film made of SiO ₂ is partially formed thereon, and a halide vapor phase is formed on the protective film. Growth method (H
This is a technique for growing the GaN layer in the lateral direction again by a vapor growth method such as VPE) or metal organic chemical vapor deposition (MOVPE). This method is generally called lateral over growth (LOG) because a nitride semiconductor is grown laterally on a protective film.

In addition, we fabricated a nitride semiconductor laser device including an active layer on a nitride semiconductor substrate fabricated 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 of growing a nitride semiconductor, the number of crystal defects is certainly smaller than that of a nitride semiconductor directly grown on a heterogeneous substrate. This is because crystal defects can be partially concentrated by LOG. In this method, crystal defects are concentrated on the upper part of the protective film, and a region with few crystal defects can be formed in the window. That is, the crystal defects can be intentionally unevenly distributed.

However, according to the conventional growth method, the number of crystal defects appearing on the surface of the nitride semiconductor is still large and is not yet satisfactory. Also, the nitride semiconductor element has insufficient reliability because crystal defects are still unevenly distributed. Therefore, even if a large number of laser elements are manufactured from a single wafer, only a small number of laser elements having a satisfactory lifetime can be obtained. In order to manufacture a device having an excellent lifetime, 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 having few crystal defects that can be used as a substrate, and to improve reliability mainly. An object is to provide an excellent nitride semiconductor device.

[0008]

According to the present invention, there is provided a method for growing a nitride semiconductor, comprising: a first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from the nitride semiconductor;
A base layer composed of a protective film partially formed on the surface of the nitride semiconductor layer and having a property that the nitride semiconductor is unlikely to grow on the surface is heated, and a nitrogen source gas and In a nitride semiconductor substrate growth method of simultaneously supplying a group source gas and growing a continuous second nitride semiconductor layer on the protective film and the underlayer, the nitrogen for the group 3 source gas may be used. It is characterized in that the molar ratio of the source gas (nitrogen source / Group III source: hereinafter referred to as V / III ratio) is adjusted to 2000 or less. A 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 at least the stoichiometric ratio, but is preferably at least 10, more preferably at least 30,
Most preferably, it is adjusted to 50 or more. In the present invention,
The nitrogen source gas corresponds to a hydride gas such as ammonia or hydrazine, and the Ga source gas may be TMG (trimethylgallium), TEG or the like in the case of metal organic chemical vapor deposition.
In the case of an organic Ga gas such as (triethylgallium) or HVPE, a gas of a Ga source is a hydrogen halide gas reacting with a group III source such as HCl, or a gallium halide (particularly GaCl ₃ ) reacting with a hydrogen halide gas. Is equivalent to

A nitride semiconductor device according to the present invention comprises a first semiconductor substrate grown on a heterogeneous substrate made of a material different from a nitride semiconductor.
And a protective film partially formed on the first nitride semiconductor layer and having a property that the nitride semiconductor does not easily grow on the surface. A second nitride semiconductor layer having a region with a large number of crystal defects on a close side and a region with a small number of crystal defects on a side distant from the underlayer, and an active layer on the second nitride semiconductor layer; Characterized in that a plurality of nitride semiconductor layers are grown.

When the underlayer is left to form an element 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 adjusted preferably in the range of 3 μm to 40 μm, more preferably in the range of 5 μm to 20 μm. The base layer has a heterogeneous substrate having a different lattice constant and thermal expansion coefficient from those of the nitride semiconductor. Therefore, the nitride semiconductor grown on the underlayer is always strained. The distortion warps the grown wafer or cracks the nitride semiconductor substrate. Therefore, by adjusting the thickness of the nitride semiconductor substrate within the above range, the warpage of the wafer can be reduced, and the cracking of the second nitride semiconductor layer can be reduced. When the thickness of the second nitride semiconductor layer is smaller than 1 μm, the second nitride semiconductor layer does not grow sufficiently on the protective film, and a crystal layer still has many defects, so that a layer serving as a substrate is formed. Hateful.

In the case where the element structure is formed by leaving the underlayer, an n-electrode is formed on an n-side contact layer made of a nitride semiconductor doped with an n-type impurity and grown on the second nitride semiconductor layer. It is characterized by being formed. Si or Ge is preferably used as the n-type impurity. If the second nitride semiconductor layer is made of undoped GaN to improve the crystallinity, the resistivity becomes higher. Therefore, a nitride semiconductor doped with an n-type impurity thereon, preferably Si-doped GaN
When the layer is a contact layer, dislocation of crystal defects is reduced, and a highly reliable element can be obtained.

In the case where the element structure is formed by leaving the underlayer, an n-electrode is formed in the second nitride semiconductor layer on the side of a region having many crystal defects. A nitride semiconductor having many crystal defects tends to have a higher carrier concentration than a nitride semiconductor having few crystal defects. Therefore,
The region of the second nitride semiconductor layer having many crystal defects naturally has n
When an n electrode is provided on the n + side, the threshold value and Vf (forward voltage) tend to decrease.

On the other hand, when the underlayer is removed to form an element structure, the thickness of the second nitride semiconductor layer is 50 μm or more. This is because when the film thickness is 50 μm or more, the region with few crystal defects further increases,
When a nitride semiconductor including an active layer is grown thereon, an element structure with very few crystal defects can be formed.

Further, when the underlayer is removed, an n-electrode is formed in the second nitride semiconductor layer in a region having many crystal defects. The underlayer is, for example, etched,
It can be separated from the nitride semiconductor substrate by a method such as polishing. Although the back surface of the second nitride semiconductor layer from which the underlayer has been removed is exposed, when an n-electrode and a p-electrode are provided as a final device, the n-electrode is formed on the entire back surface and the active layer is formed. The p-electrode provided on the nitride semiconductor layer side including the layer and the n-electrode face each other. Since the second nitride semiconductor layer has a low carrier concentration region having the same composition and having few crystal defects and a high carrier concentration region having many crystal defects, by providing an 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, one having the least crystal defects, a high mobility and a low carrier concentration tends to be obtained. In order to increase the impurity concentration, growth may be performed by doping an n-type impurity. In particular, when an electrode is formed on the surface of the second nitride semiconductor layer by removing the base 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. However, in the device of the present invention, the second nitride semiconductor layer is If the region having a large number of crystal defects and the region having a small number of crystal defects are substantially in the same direction with respect to the nitride semiconductor laminating direction,
The growth method is not particularly limited.

[0017]

1 to 4 are schematic sectional views showing a crystal structure of a second nitride semiconductor layer formed by a growth method according to the present invention, while FIGS. 5 to 7 show nitrogen source gas. FIG. 4 is a schematic cross-sectional view showing a crystal structure of a nitride semiconductor layer according to a conventional growth method with a small supply amount of. In these figures,
1, 1 'is a heterogeneous substrate made of, for example, 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 does not easily grow on the surface. Reference numerals 4, 4 'denote second nitride semiconductor layers serving as substrates. Hereinafter, the operation of the nitride semiconductor growth method of the present invention will be described with reference to these drawings while comparing with the conventional method. 1 to 7 schematically show crystal defects of the nitride semiconductor.

The first nitride semiconductor layer 2 grown on the heterogeneous substrate 1 has crystal defects almost uniformly in the layer. Then, a protective film 3 is formed partially (for example, in a stripe shape) 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. to form a continuous second nitride on the surface of the base layer. The semiconductor layer 4 is grown.

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

When the growth is further continued, the nitride semiconductor grows upward on the protective film 3 but also grows laterally (LOG). According to the method of the present invention, the end face of the second nitride semiconductor 4 grows almost perpendicularly to the horizontal plane of the heterogeneous substrate, so that the second nitride semiconductor 4 is close to the protective film as shown in FIG. There is a tendency that the connection is made earlier on the side farther from the protective film than on the side, or the end faces are connected almost simultaneously. What is important here is that the crystal defects occurring in the second nitride semiconductor layer hardly appear on the surface of the second nitride semiconductor layer because they extend in the lateral direction.

When the growth is further continued, the second nitride semiconductor layer 4 also grows upward. However, as shown in FIG. 3, the second nitride semiconductor layer 4 is formed in a lateral direction so as to fill a void just above the protective film.
Or it grows downward. In accordance with the growth, the crystal defects of the second nitride semiconductor layer 4 tend to grow in the direction of the protective film 3 or spread right beside them.

Therefore, the grown second nitride semiconductor layer 4
This is because, as shown in FIG. 4, 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, and do not lead to the surface to form threading dislocations. What appears on the surface is very small. In some cases, when a thick film is grown, crystal defects stop during the growth. For this reason, as the second nitride semiconductor layer grows thicker on the underlayer, crystal defects tend to decrease.
m, a second nitride semiconductor layer with very few crystal defects appearing on the surface is obtained.
Acts as an aN substrate.

By growing the second nitride semiconductor in this manner, the second nitride semiconductor having a region with many crystal defects on the side close to the underlayer and a region with few crystal defects on the side far from the underlayer is formed. A 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 reduced to 1 × 10 ⁸ / cm ² or less and further 1 × 10 ⁶ / cm ² or less when observed by a cross-sectional TEM. .

On the other hand, in the conventional growth method shown in FIGS. 5 to 7 in which the V / III ratio is larger than 2,000, the second nitride semiconductor layer 4 grown from the window as shown in FIG. 'Grows in the shape of a triangle (roof) at the window. When the second nitride semiconductor layer 4 ′ grows in a triangular shape, crystal defects extending from the first nitride semiconductor layer 2 ′ to the second nitride semiconductor layer 4 ′ are formed on the triangular sides (the roof portion). ).

When the growth is further continued, the second nitride semiconductor layer 4 'grows in the lateral direction and is connected first on the surface of the protective film, which is the base of the triangle. As we continue to grow,
Crystal defects toward the roof also extend upward.

Therefore, crystal defects of the second nitride semiconductor layer 4 ′ formed by the conventional growth method are connected at the upper part of the protective film and become threading dislocations on the surface of the second nitride semiconductor layer, as shown in FIG. appear. Therefore, a region with many crystal defects and a region with 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 perpendicular to the substrate or in an inverted trapezoidal shape, the molar ratio between the nitrogen source gas and the group III source gas is adjusted. It is very important that the ratio (nitrogen source /
If the number of (Group 3 source) is more than 2,000, the second nitride semiconductor grows in a triangular shape as in the related art, so that it tends to be difficult to obtain a second nitride semiconductor layer with 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, and also shows a cross section taken along a direction perpendicular to a ridge stripe. I have. Hereinafter, the first embodiment will be described with reference to FIG.

A heterogeneous substrate 1 made of sapphire having a 2-inch diameter and a C-plane as a main surface is set in a MOVPE reactor, the temperature is set to 500 ° C., hydrogen is used as a carrier gas, and TMG (trimethylgallium (Ga) is used as a reaction gas. (CH ₃ ) ₃ : T
A buffer layer (not shown) made of GaN is grown to a thickness of 200 Å using MG) and ammonia (NH ₃ ). After growing the buffer layer, the temperature is set to 1050
C., the first nitride semiconductor layer 2 also made of GaN is grown to a thickness of 5 μm. The first nitride semiconductor layer 2 is made of Al _x Ga ₁ -xN (0
≤ X ≤ 0.5). If it exceeds 0.5, the crystal itself tends to be cracked rather than a crystal defect, and the crystal growth itself tends to be difficult. Further, it is desirable that the film is grown to a thickness larger than that of the buffer layer and adjusted to a thickness of 10 μm or less. In addition to sapphire, a substrate made of a material different from a nitride semiconductor, such as SiC, ZnO, spinel, and 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 vessel and the first nitride semiconductor layer 2 is removed.
Form a striped photomask on the surface of
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 to a thickness of 1 μm by the D apparatus. The shape of the protective film is striped,
Although any shape such as a dot shape or a grid shape may be used, the second nitride semiconductor layer 3 having less crystal defects is more likely to grow when the area of the protective film is larger than that of the window portion. Examples of the material of the protective film include oxides and nitrides such as silicon oxide (SiO _x ), silicon nitride (Si _x N _y ), titanium oxide (TiO _x ), and zirconium oxide (ZrO _x ), and multilayer films thereof. In addition, a metal having a melting point of 1200 ° C. or more can be used. These protective film materials withstand the growth temperature of the nitride semiconductor of 600 ° C. to 1100 ° C., and have a property that the nitride semiconductor does not grow or hardly grows on the surface thereof.

(Second Nitride Semiconductor Layer 4) After the formation of the protective film 3, the wafer is set again in the MOVPE reaction vessel, the temperature is set at 1050 ° C., and ammonia is added at 0.27 mol.
l / min, TMG at 225 μmol / min (V / III ratio = 12
00), a second nitride semiconductor layer 4 made of undoped GaN is grown to a thickness of 30 μm. After the growth, when the second nitride semiconductor layer is observed with a cross-sectional TEM, the number of crystal defects in the region from the interface of the first nitride semiconductor layer to about 5 μm is large (10 ⁸ / cm ² or more). In the region above 5 μm, there were few crystal defects (10 ⁶ / cm ² or less), and the region was sufficiently usable as a nitride semiconductor substrate. On the surface after the growth, almost no crystal defects are observed on the upper part of the protective film, and crystal defects tend to appear slightly on the upper part of the window (the center of the stripe). Is greater than 2,000), the number of crystal defects is two orders of magnitude or less.

The second nitride semiconductor layer can be grown by using the halide vapor phase epitaxy (HVPE), but can also be grown by the MOVPE method.
Most preferably, the second nitride semiconductor layer is made of GaN that does not contain In or Al. As a gas for the growth, in addition to TMG, triethylgallium (Ga (C
₂ H _{5) 3:} an organic gallium compounds of the TEG) or the like, a nitrogen source is most preferable to use ammonia or hydrazine. In addition, Si,
The carrier concentration may be adjusted to an appropriate range by doping n-type impurities 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 = n-side contact layer) Next, using ammonia and TMG, and silane gas as an impurity gas, Si is deposited on the second nitride semiconductor
An n-side buffer layer 11 of GaN doped with × 10 ¹⁸ / cm ³ is grown to a thickness of 5 μm. When a light emitting device having a structure as shown in FIG.
It also functions as a contact layer for forming an electrode.
In the case where an electrode is provided on the second nitride semiconductor layer after removing the heterogeneous substrate and the protective film, the step can be omitted. The n-side buffer layer is a buffer layer grown at a high temperature, for example, on a substrate made of a material different from a nitride semiconductor such as sapphire, SiC, or spinel, for example.
GaN, AlN, etc., at a low temperature
It is distinguished from a buffer layer directly grown with a thickness of less than m.

(Crack prevention layer 12) Next, TMG, T
Using MI (trimethylindium) and ammonia at a temperature of 800 ° C., a crack prevention layer 12 of In _0.06 Ga _0.94 N is grown to a thickness of 0.15 μm. The crack preventing layer is formed by growing a nitride semiconductor containing at least indium, preferably In _x Ga ₁ -xN (0 <x <0.5), to a thickness of 0.5 μm or less, and thereby growing an Al on the nitride semiconductor. Cracks can be prevented from entering the nitride semiconductor containing.

(N-side cladding layer 13 = superlattice layer) Subsequently, n-type A doped with Si at 1 × 10 ¹⁹ / cm ³ using TMA, TMG, ammonia and silane gas at 1050 ° C.
A first layer of l _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 as a first layer + second layer + first layer + second layer +..., And an n-side cladding layer 12 composed of a superlattice having a total film thickness of 0.8 μm is grown. When a superlattice in which nitride semiconductors having different band gap 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 light guide layer 14) Subsequently, the silane gas is stopped and the n-side light guide layer 14 made of undoped GaN is grown at 1050 ° C. to a thickness of 0.1 μm. This n-side light guide layer acts as a light guide layer of the active layer,
It is desirable to grow GaN or InGaN, usually 100 Å to 5 μm, more preferably 2 Å.
It is desirable to grow with a film thickness of 00 Å to 1 μm. This layer can also be an undoped superlattice layer. In the case of a superlattice layer, the bandgap energy of the nitride semiconductor layer having the larger bandgap energy constituting 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 maintained at 800 ° C., and a well layer made of undoped In _0.2 Ga _0.8 N is grown to a thickness of 40 Å. Next, a barrier layer made of undoped In _0.05 Ga _0.95 N was added at the same temperature only by changing the molar ratio of TMI.
It is grown to a thickness of 00 Å. A well layer and a barrier layer are sequentially stacked, and finally terminated with a barrier layer.
An active layer of 40 Å multiple quantum well structure (MQW) is grown. The active layer may be undoped as in this embodiment, or may be doped with an n-type impurity and / or a p-type impurity. The impurity may be doped into both the well layer and the barrier layer, or may be doped into either one.

(P-side cap layer 16)
Raise to 50 ° C, TMG, TMA, ammonia, Cp2M
g (cyclopentadienyl magnesium), p-type Al _0.3 Ga doped with Mg at 1 × 10 ²⁰ / cm ³ and having a larger band gap energy than the p-side light guide layer 17
_A p-side cap layer 16 of _0.7 N is grown to a thickness of 300 Å. When the p-type cap layer 16 is formed with a thickness of 0.1 μm or less, the output of the device tends to be improved. Although the lower limit of the film thickness is not particularly limited, it is desirable to form the film with a film thickness of 10 Å 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 band gap energy smaller than that of the p-side cap layer 16 is grown to a thickness of 0.1 μm. This layer acts as a light guide layer of the active layer and, like the n-type light guide layer 14, GaN, InGaN
It is desirable to grow with. The p-side light guide layer may be a superlattice layer made of an undoped nitride semiconductor or a nitride semiconductor doped with a p-type impurity. In the case of forming a superlattice layer, 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 cladding layer 18)
P-type Al _0.2 Ga doped with Mg at 1 × 10 ²⁰ / cm ³
_A third layer of _0.8 N is grown to a thickness of 25 Å, followed by stopping only TMA and undoping Ga.
A fourth layer of N is grown to a thickness of 25 Å, and a p-side cladding layer 18 of a superlattice layer having a total thickness of 0.8 μm is grown. This layer is also the n-side cladding layer 13
In the case where a superlattice in which nitride semiconductors having different band gap energies are stacked as in the above case 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.

(P-side contact layer 19) Finally, 105
At 0 ° C., 2 × 10 ²⁰ Mg is applied on the p-side cladding layer 18.
A p-side contact layer 18 made of p-type GaN doped with / cm ³ is grown to a thickness of 150 Å. p
The side contact layer 19 is a p-type In _x Al _Y Ga _{1 -XYN}
(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
Because a nitride semiconductor having a small band gap energy is used as a p-side contact layer in contact with the p-side cladding layer 17 having a superlattice structure containing l _Y Ga _1-Y N, the film thickness is reduced to 500 Å or less. In addition, the carrier concentration of the p-side contact layer 18 is substantially increased, a favorable 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 nitrogen atmosphere in a reaction vessel.
Annealing is performed at a temperature of ° C. to further reduce the resistance of the layer doped with the p-type impurity.

After annealing, the wafer is taken out of the reaction vessel, and as shown in FIG. 7, the uppermost p-side contact layer 18 and p-side clad layer 17 are etched by an RIE apparatus to have a stripe width of 4 μm. Ridge shape. Importantly, when forming a ridge stripe, as shown in FIG. 8, the position of the ridge stripe is set to a position avoiding the center of a stripe-shaped window portion where crystal defects tend to appear slightly. When a stripe is formed at a position where there is almost no crystal defect, the crystal defect tends not to extend to the active layer, so that the life of the element can be extended and the reliability is improved.

Next, a mask is formed on the ridge surface, and RIE 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 a contact layer in FIG. 8, etching is performed up to a region of the second nitride semiconductor layer 4 where there are many crystal defects, and the second nitride semiconductor layer 4 is used as a contact layer. Can also.

Next, a p-electrode 20 made of Ni and Au is formed in a stripe shape on the outermost surface of the ridge of the p-side contact layer 19. Examples of the material of the p-side contact layer and the p-electrode 20 that provides a preferable ohmic material include Ni, Pt, and P.
d, Co, Ni / Au, Pt / Au, Pd / Au and the like.

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

Next, as shown in FIG.
The surface of the nitride semiconductor layer exposed between the
An insulating film 23 made of O ₂ is formed, and a p-pad electrode 21 electrically connected to the p-electrode 20 via the insulating film 23 is formed. This p pad electrode 21 is substantially a p electrode 21
Wire bonding on the p-electrode side,
Die bonding is possible.

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

Thereafter, the Au / Sn side is scribed,
Cleavage is performed in a bar shape in a direction perpendicular to the stripe-shaped electrodes, and a resonator is formed on the cleavage plane. SiO ₂ and TiO ₂ on the resonator surface
A dielectric multilayer film was formed, and finally the bar was cut in a direction parallel to the p-electrode to form a laser chip. Next, the chip was placed face-up (in a state in which the substrate and the heat sink faced each other), and the electrodes were wire-bonded and laser oscillation was attempted at room temperature. At room temperature, the threshold current density was 2.0 kA / At cm ² and a threshold voltage of 4.0 V, continuous oscillation with an oscillation wavelength of 405 nm was confirmed, and a lifetime of 10,000 hours or more was shown. Further, 500 laser elements were randomly extracted from the same wafer, and the life of the laser elements was measured. As a result, 70% or more showed a life of 10,000 hours or more.

[Comparative Example] In Example 1, when growing the second nitride semiconductor layer 4, 0.36 mol of ammonia was added.
l / min, TMG at 162 μmol / min (V / III ratio = 22
22) A laser element was obtained in the same manner as in 22) except that a second nitride semiconductor layer 4 made of undoped GaN was grown to a thickness of 30 μm and a ridge stripe was formed at an arbitrary position. The sample which achieved 10,000 hours or more was 5% or less.

Example 2 A laser device was fabricated in the same manner as in Example 1 except that the thickness of the second nitride semiconductor was changed to 10 μm when growing the second nitride semiconductor. The number of crystal defects appearing on the surface of the sample tended to be about an order of magnitude larger than that in Example 1, and 50% or more of the 500 samples that achieved 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 indicate the same parts. The second embodiment will be described below with reference to FIG.

In the first embodiment, the second nitride semiconductor layer 4
Was grown at 0.27 mol / min with T
The MG is set to 150 μmol / min (V / III ratio = 1800), and a silane gas is further added to grow a second nitride semiconductor layer made of Si-doped GaN to a thickness of 30 μm. In the region from the interface between the second nitride semiconductor layer 4 and the first nitride semiconductor layer 2 to about 5 μm, the number of crystal defects is large, and in the region above 5 μm, the number of crystal defects is small (10 ⁷ / cm ² or less), and could be sufficiently used as a nitride semiconductor substrate.

Thereafter, 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 from above the second nitride semiconductor layer by etching. Then, the surface of the second nitride semiconductor layer 4 in the region having many crystal defects is exposed, and n
The electrode 22 is formed to form a laser device. As in the case of the first embodiment, this laser device continuously oscillates at a low threshold value, and at least 50% of 500 laser devices have achieved a life of 10,000 hours or more.

Fourth Embodiment In the first embodiment, when growing the second nitride semiconductor layer 4, ammonia was added at a rate of 0.2%.
7 mol / min, 180 μmol / min TMG (V / III ratio =
A laser device was manufactured in the same manner as in Example 1 except that the laser device was changed to 1500). As a result, continuous oscillation was performed at the same low threshold value, and the number of laser devices substantially equal to that in Example 1 was obtained.

Fifth Embodiment In the first embodiment, except that the flow rate of only TMG is increased and the V / III ratio is set to 800 when the second nitride semiconductor layer 4 is grown. When a laser element was manufactured in the same manner as in Example 1, continuous oscillation was performed at the same low threshold value, and the number of laser elements obtained was almost the same as in Example 1.

[Embodiment 6] In Embodiment 1, when growing the second nitride semiconductor layer 4, ammonia was added at 0.1%.
5 mol / min, TMG at 5 mmol / min (V / III ratio = 30)
A laser device was fabricated in the same manner as in Example 1 except that the laser device was continuously oscillated at a low threshold value, and 30% or more out of 500 laser devices having a lifetime of 10,000 hours or more.

[Embodiment 7] In the embodiment 1, when growing the second nitride semiconductor layer 4, it is doped with Si and grown to a thickness of 90 μm. Thereafter, a nitride semiconductor layer including an active layer is grown on the second nitride semiconductor layer in the same manner as in the first embodiment. After the growth, when the wafer was taken out of the reaction vessel, 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 different substrate side of the wafer is polished to remove the different substrate 1, the first nitride semiconductor layer 2, and the protective film 3. The removal of the dissimilar substrate allowed the wafer to be obtained almost flat.

Next, a p-side electrode 20 and a p-pad electrode 21 are formed in a ridge shape from the p-side cladding layer 18 in the same manner as in the first embodiment. However, it is difficult to match the position of the ridge stripe with the window since the protective film has been 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 the protective film is removed and exposed to many crystal defects, and a laser in which the p-electrode and the n-electrode face each other. Element.

Similarly, this laser device continuously oscillates at room temperature at a low threshold value and has a lifetime of 10,000 hours or more.
More than 70% of the individual.

[0061]

As described above, according to the nitride semiconductor growth method of the present invention, it is possible to realize a nitride semiconductor element in which crystal defects appearing on the surface are very few without crystal defects concentrated 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, a highly reliable device can be realized. .

[Brief description of the drawings]

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

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

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

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

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

FIG. 7 is a cross-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 one 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]

 DESCRIPTION OF SYMBOLS 1 ... Different substrate 2 ... 1st nitride semiconductor layer 3 ... Protective film 4 ... 2nd nitride semiconductor layer 11 ... n side buffer layer 12 ... Crack prevention layer 13 ... n-side cladding layer 14 ... n-side light guide layer 15 ... active layer 16 ... p-side cap layer 17 ... p-side light guide layer 18 ... p-side cladding layer 19 ...・ P-side contact layer 20 ・ ・ ・ p electrode 21 ・ ・ ・ p pad electrode 22 ・ ・ ・ n electrode 23 ・ ・ ・ insulating film

Claims (9)

[Claims] A first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from the nitride semiconductor; a first nitride semiconductor layer partially formed on a surface of the first nitride semiconductor layer, and a nitride Heating a base layer made of a protective film having a property in which a semiconductor is unlikely to grow, and simultaneously supplying a nitrogen source gas and a group III source gas to the surface of the base layer, In the method for growing a nitride semiconductor in which a continuous second nitride semiconductor layer is grown, the molar ratio of the nitrogen source gas to the group III source gas (nitrogen source / group III source) is set to 2000 or less. A method for growing a nitride semiconductor, comprising adjusting. 2. A first nitride semiconductor layer grown on a heterogeneous substrate made of a material different from a nitride semiconductor, and a first nitride semiconductor layer partially formed on the first nitride semiconductor layer and having a nitrided surface. A region having many crystal defects on a side close to the underlayer, and a region having few crystal defects on a side away from the underlayer, on a base layer made of a protective film having a property that the semiconductor hardly grows. 2. A nitride semiconductor device, comprising: a plurality of nitride semiconductor layers; and a plurality of nitride semiconductor layers including an active layer grown on the second nitride semiconductor layer. 3. The nitride semiconductor device according to claim 2, wherein the underlayer is left, and the thickness of the second nitride semiconductor layer is in a range of 1 μm to 50 μm. 4. An n-electrode is formed on an n-side contact layer formed of a nitride semiconductor doped with an n-type impurity and grown on the second nitride semiconductor layer while leaving the base layer. The nitride semiconductor device according to claim 2, wherein 5. The nitride according to claim 2, wherein the n-electrode is formed in the second nitride semiconductor layer on the side of the region where the number of crystal defects is large while leaving the base layer. Semiconductor element. 6. The nitride semiconductor device according to claim 2, wherein the underlayer is removed, and the thickness of the second nitride semiconductor layer is 50 μm or more. 7. The nitride semiconductor device according to claim 2, wherein the underlayer is removed, and an n-electrode is formed in the second nitride semiconductor layer on the side of the region having more crystal defects. . 8. The nitride semiconductor device according to claim 2, wherein said second nitride semiconductor layer is doped with an n-type impurity. 9. The nitride according to claim 2, wherein the second nitride semiconductor layer is grown by the method according to claim 1. Description: Semiconductor element.