JP2002016000A - Nitride semiconductor element and nitride semiconductor substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nitride semiconductor substrate capable of causing a nitride semiconductor layer having proper crystallinity to grow. SOLUTION: An n-GaN off substrate 1 comprises an off surface tilted 1-20 deg.C from (0001) plane. Here, the tilt direction of the off surface is in the direction ±7 deg.C from <11-20> direction. When a nitride semiconductor layer is grown on the n-GaN off substrate 1 comprising the off surface, the crystal growth of the nitride semiconductor layer takes place mainly in step flow mode. Thus, using the n-GaN off substrate 1, a nitride semiconductor layer of proper crystallinity can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a nitride semiconductor device such as a light emitting diode device, a semiconductor laser device, a light receiving device, a transistor and the like using a group III nitride semiconductor (hereinafter referred to as a nitride semiconductor). The present invention relates to a nitride semiconductor substrate used for such a nitride semiconductor device.

[0002]

2. Description of the Related Art In recent years, research and development of semiconductor devices using nitride semiconductors such as GaN have been advanced.

FIG. 11 is a schematic sectional view showing an example of a conventional nitride semiconductor laser device. As shown in FIG. 11, a semiconductor laser device includes a sapphire substrate 81, a buffer layer 82, an undoped GaN layer 83, an n-GaN contact layer 84, an n-AlGaN cladding layer 85, an n-G
The aN light guide layer 86, the light emitting layer 87, and the p-GaN light guide layer 88 are sequentially formed. p-GaN optical guide layer 8
8, a ridge-shaped p-AlGaN cladding layer 89 is formed on the region having a predetermined width.
A current confinement layer 91 is formed on the side surface of the aN clad layer 89. Further, a p-GaN contact layer 90 is formed on the upper surface of the p-AlGaN cladding layer 89 and the current confinement layer 91.
Are formed. From the p-GaN contact layer 90 to n
A part of the region up to the -GaN contact layer 84 is removed to expose the n-GaN contact layer 84, forming a mesa shape. An n-electrode 93 is formed on a predetermined region of the exposed n-GaN contact layer 84, and a p-electrode 92 is formed on a predetermined region of the p-GaN contact layer 90.

In the semiconductor laser device shown in FIG.
In order to effectively confine the light generated in the light emitting layer 87 and to obtain a good vertical far-field image,
The difference in the refractive index between the n-AlGaN cladding layer 85 and the n-GaN optical guide layer 86 and the p-AlGaN cladding layer 8
9 and the difference in the refractive index between the p-light guide layer 88 and the n-AlGaN cladding layer 85 and the p-
It is necessary to increase the thickness of the AlGaN cladding layer 89.

[0005]

The difference in the refractive index between the n-AlGaN cladding layer 85 and the n-GaN optical guide layer 86,
As a method for increasing the difference in the refractive index between the p-AlGaN cladding layer 89 and the p-light guide layer 88, nA
It is conceivable to increase the Al composition of the lGaN cladding layer 85 and the p-AlGaN cladding layer 89.

However, since the surface diffusion of Al atoms during crystal growth is small, if the Al composition is increased in the n-AlGaN cladding layer 85 and the p-AlGaN cladding layer 89, good crystallinity in these layers 85 and 89 is obtained. Is difficult to achieve.

In order to improve the crystallinity of the p-AlGaN cladding layer 89 and the n-AlGaN cladding layer 85 having a large Al composition, these layers 85, 8
It is necessary to increase the substrate temperature during the growth of No. 9. However, even when these layers 85 and 89 are grown at a high temperature, sufficiently good crystallinity cannot be obtained.

Furthermore, in this case, since the lattice constant of AlGaN is smaller than the lattice constant of GaN, the n-AlGaN cladding layer 85 and the p-AlGaN cladding layer 89 having a large Al composition and degraded crystallinity as described above. Cracks easily occur.

In the p-AlGaN cladding layer 89, it is usually difficult to increase the carrier concentration due to the low activation rate of Mg.
In the p-AlGaN cladding layer 89 having a large 1 composition, the carrier concentration cannot be increased because the crystallinity is deteriorated.

From the above, it is difficult to increase the Al composition in the n-AlGaN cladding layer 85 and the p-AlGaN cladding layer 89.

On the other hand, even when the thicknesses of the n-AlGaN cladding layer 85 and the p-AlGaN cladding layer 89 are increased, the lattice constant of AlGaN is G as described above.
These layers 8 are smaller than the lattice constant of aN.
At 5, 89, cracks easily occur. Therefore, the n-AlGaN cladding layer 85 and the p-AlGa
It is difficult to increase the thickness of the N cladding layer 89.

As described above, in the above semiconductor laser device, the n-AlGaN cladding layer 85 and the p-A
Since it is difficult to increase the Al composition and the film thickness in the lGaN cladding layer 89, it is difficult to improve the device characteristics of the semiconductor laser device.

On the other hand, a light receiving element made of a nitride semiconductor,
In particular, in a light-receiving element having high sensitivity to light in the ultraviolet region having a wavelength shorter than 300 nm, the light-receiving portion Al
It is necessary to increase the Al composition and the film thickness of the GaN layer.

However, as described above, in an AlGaN layer having a large Al composition and a large film thickness, the crystallinity is easily deteriorated and cracks are easily generated. For this reason, it is difficult to increase the Al composition and the film thickness of the AlGaN layer of the light receiving section. Therefore, it is difficult to realize a light receiving element having high sensitivity to short wavelength light.

Meanwhile, in a nitride-based semiconductor device having a GaN-based semiconductor layer formed on a sapphire substrate, the difference in lattice constant between the sapphire substrate and the GaN-based semiconductor layer is large. For this reason, the GaN-based semiconductor layer formed on the sapphire substrate contains many dislocations and has deteriorated crystallinity. Therefore, it is difficult to realize good device characteristics in a nitride semiconductor device using a sapphire substrate.

Therefore, research on a nitride semiconductor device using a SiC substrate or a GaN substrate having a lattice constant closer to that of a nitride semiconductor than a sapphire substrate instead of the sapphire substrate has been conducted.

Further, attempts have been made to improve the crystallinity of the nitride-based semiconductor layer formed on the SiC substrate by forming an inclined surface (off-surface) on the surface.

For example, in JP-A-11-233391, a value of 0.0
A SiC substrate having a plane (off plane) inclined within a range of 2 degrees to 0.6 degrees is disclosed. By using a SiC substrate having an off-plane inclined at such an angle, in growing a nitride-based semiconductor layer on the SiC substrate,
A growth surface of the nitride semiconductor having an off angle equal to the off angle of the SiC substrate is formed. As a result, it is shown that good crystallinity can be obtained in the nitride-based semiconductor layer by growing the nitride-based semiconductor layer in the step flow mode. Further, in a GaN substrate, the above S
It has been suggested that forming an off-plane similar to an iC substrate would be effective. Also, here, 3.5
Laser oscillation does not occur in a semiconductor laser device manufactured using a SiC substrate having an off-plane having a large inclination of °°, and as a cause, it is shown that unevenness with a step of about 100 nm is formed on the GaN surface. I have.

However, the present inventor disclosed in Japanese Patent Application Laid-Open
0.03 similar to the SiC substrate disclosed in US Pat.
When a nitride-based semiconductor layer grown on a GaN substrate having an off-plane of 2 degrees to 0.6 degrees was examined, a nitride-based semiconductor layer grown on a GaN substrate having such an off-plane, particularly, It has been clarified that sufficiently good crystallinity cannot be obtained in a nitride-based semiconductor layer having Al such as AlGaN.

An object of the present invention is to provide a nitride semiconductor device in which the device characteristics are improved by improving the crystallinity of the nitride semiconductor layer.

Another object of the present invention is to provide a nitride semiconductor substrate on which a nitride semiconductor layer having good crystallinity can be grown.

[0022]

As a result of various experiments and studies conducted by the present inventor, the present inventors have found that the GaN substrate has an off-angle based on a concept reverse to that disclosed in Japanese Patent Application Laid-Open No. 11-233391. Is larger than the range of 0.02 to 0.6 degrees, a nitride-based semiconductor layer having good crystallinity can be obtained. And based on this result, the following present invention was devised.

A nitride-based semiconductor substrate according to the present invention is a nitride-based semiconductor substrate made of a hexagonal nitride-based semiconductor, and has an inclined surface inclined at a predetermined angle from a (0001) plane in a predetermined direction. And the inclination angle of the inclined surface is 1 degree or more and 20 degrees or less.

At the inclined surface of the nitride-based semiconductor substrate according to the present invention, a step of an atomic order is formed. Here, when a nitride-based semiconductor layer is grown on an inclined surface of a nitride-based semiconductor substrate having such a step of the atomic order, growth occurs mainly in the step-flow mode in the nitride-based semiconductor layer. . Thereby, in the nitride-based semiconductor layer formed on the nitride-based semiconductor substrate, dislocations are reduced and good crystallinity is realized.

Further, such a nitride-based semiconductor substrate,
The difference in lattice constant between the nitride-based semiconductor layer grown thereon and the nitride-based semiconductor layer is reduced. Therefore, when a nitride-based semiconductor layer is grown using such a nitride-based semiconductor substrate, it is necessary to reduce dislocations generated in the nitride-based semiconductor layer due to a difference in lattice constant from the substrate. And good crystallinity can be realized.

As described above, by using the nitride-based semiconductor substrate according to the present invention, it is possible to realize good crystallinity in the nitride-based semiconductor layer formed thereon. Accordingly, by manufacturing a nitride-based semiconductor device using the nitride-based semiconductor substrate according to the present invention, it is possible to obtain a nitride-based semiconductor device with improved device characteristics.

The inclination direction of the inclined surface is preferably a direction in the range of 0 to 7 degrees from the <11-20> direction in the substrate plane, or a direction equivalent thereto. In the hexagonal nitride semiconductor, the [11-20] direction, the [-2110] direction, and [-12-1]
The [0], [-1-120], [2-1-10] and [1-210] directions are equivalent plane directions. Here, these equivalent plane orientations are represented by the general notation <11-20>.

When a nitride-based semiconductor layer is formed on a nitride-based semiconductor substrate having an inclined surface in the above-described inclination direction, a step of a monoatomic layer is easily formed on the surface of the nitride-based semiconductor layer. As a result, the interval between the steps is reduced, and the crystal growth of the nitride-based semiconductor layer is more likely to occur in the step mode. Therefore, in this case, a nitride semiconductor having good crystallinity can be formed.

The nitride-based semiconductor substrate may be made of GaN. When a nitride-based semiconductor layer is formed on such a GaN substrate, the difference in lattice constant between the GaN substrate and the nitride-based semiconductor layer can be reduced. For this reason, in the nitride-based semiconductor layer, it is possible to reduce dislocations generated due to a difference in lattice constant from the substrate. Therefore, a nitride-based semiconductor layer having better crystallinity can be formed.

A nitride-based semiconductor device according to the present invention comprises a nitride-based semiconductor substrate formed of a hexagonal nitride-based semiconductor and one or more nitride-based semiconductor layers formed on the substrate. And the nitride semiconductor substrate is (000
1) It has an inclined surface inclined at a predetermined angle from the surface in a predetermined direction, and the inclination angle of the inclined surface is 1 degree or more and 20 degrees or less.

In the nitride semiconductor device according to the present invention, a nitride semiconductor substrate having an inclined surface inclined at a predetermined angle within a range of 1 ° to 20 ° from a (0001) plane in a predetermined direction is used. Have been. At the inclined surface of such a nitride-based semiconductor substrate, a step of an atomic order is formed.

When one or more nitride-based semiconductor layers are grown on the inclined surface of the nitride-based semiconductor substrate on which the steps of the atomic order are formed, the nitride-based semiconductor layer mainly has a step flow. Growth occurs in the mode.
Thereby, in the nitride-based semiconductor layer, dislocations are reduced and good crystallinity is realized.

In this case, since the lattice constant of the nitride-based semiconductor substrate is close to the lattice constant of the nitride-based semiconductor layer, the nitride-based semiconductor layer is generated due to a difference in lattice constant from the substrate. Dislocations are reduced. Therefore, in the nitride-based semiconductor layer formed on the nitride-based semiconductor substrate, the crystallinity is further improved.

As described above, in the above-described nitride semiconductor device provided with the nitride semiconductor substrate, it is possible to obtain good crystallinity in the nitride semiconductor layer. For this reason, in the nitride-based semiconductor device, it is possible to improve the device characteristics.

The inclination direction of the inclined surface of the nitride-based semiconductor substrate is preferably in the range of 0 ° to 7 ° from the <11-20> direction in the substrate plane.

On the nitride-based semiconductor substrate having the inclined surface in the above-described inclined direction, a step of a monoatomic layer is easily formed on the surface of the nitride-based semiconductor layer, and as a result, the interval between the steps is short. Thus, the crystal growth of the nitride-based semiconductor layer is more likely to occur in the step mode. Therefore,
In this case, good crystallinity is realized in the nitride-based semiconductor layer.

The nitride-based semiconductor substrate may be composed of GaN. By growing a nitride-based semiconductor layer on such a substrate made of GaN, the difference in lattice constant between the substrate and the nitride-based semiconductor layer can be reduced. For this reason, in the nitride-based semiconductor layer, it is possible to reduce dislocations generated due to a difference in lattice constant from the substrate. Therefore, a nitride-based semiconductor layer having better crystallinity can be formed, and the device characteristics of the nitride-based semiconductor device are improved.

The nitride semiconductor layer may be composed of at least one or more nitride semiconductor layers containing Al.

Here, since the surface diffusion of Al during crystal growth is usually small, crystal growth hardly occurs in the step flow mode in a nitride-based semiconductor layer having a large Al composition. Therefore, it is difficult to realize good crystallinity in a nitride-based semiconductor layer having a large Al composition.

On the other hand, in this case, a nitride semiconductor layer containing Al is formed on a nitride semiconductor substrate having an inclined surface. Therefore, in the nitride-based semiconductor layer containing Al, crystal growth can proceed in the step flow mode even when the Al composition is increased. Therefore, in this case, it is possible to increase the Al composition and improve the crystallinity in the nitride-based semiconductor layer containing Al.

In such a nitride semiconductor device having a nitride semiconductor layer containing Al having a large Al composition and good crystallinity, the device characteristics can be improved.

Further, the nitride-based semiconductor layer may be constituted by forming a first nitride-based semiconductor layer, an active element region and a second nitride-based semiconductor layer in this order.
The active element region of the nitride-based semiconductor element in this case is, for example, a light emitting layer or an active layer of a light emitting diode element or a semiconductor laser element, a core layer of a waveguide element, an I layer of a PIN photodiode, a photodiode or an HBT. (A heterojunction bipolar transistor), a channel portion of an FET (field effect transistor), and the like.

In this case, growth occurs mainly in the step flow mode in the first and second nitride semiconductor layers and the active element region. Therefore, in the first and second nitride-based semiconductor layers and the active element region, dislocations are reduced, and good crystallinity is realized.

The first nitride-based semiconductor layer may include a nitride-based semiconductor layer containing Al, and the second nitride-based semiconductor layer may include a nitride-based semiconductor layer containing Al. Further, the first nitride-based semiconductor layer containing Al and the second nitride-based semiconductor layer containing Al may be made of AlGaN.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing a nitride semiconductor substrate according to the present invention will be described below.

FIG. 1 is a schematic process sectional view showing an example of a method for manufacturing a nitride semiconductor substrate according to the present invention.

First, as shown in FIG.
1) An n-GaN substrate 1a having a surface as a main surface is prepared.

Next, as shown in FIG.
-A region of the n-GaN substrate 1a on the A line is removed by polishing. As a result, a surface (hereinafter, referred to as an off surface) inclined by a predetermined angle (hereinafter, referred to as an off angle) B in a predetermined direction (hereinafter, referred to as an off direction) from the (0001) plane is exposed.

Here, the off-angle B in the n-GaN substrate 1 is a predetermined angle in the range of 1 to 20 °. In addition, the off direction corresponds to <11−20 of GaN in the substrate plane.
> A predetermined direction within a range of ± 7 ° from the direction.

Here, the [11-20] direction and directions equivalent thereto are represented by the general notation <11-20> direction.

As described above, as shown in FIG. 1C, an n-GaN off-substrate 1 having an off-surface formed on the surface is manufactured. In this case, a step in the order of atoms is formed on the surface of the n-GaN off-substrate 1, that is, on the off-surface. FIG. 1C is a schematic diagram in which a step in the order of atoms is exaggerated in the height direction.

In another method for manufacturing a nitride semiconductor substrate according to the present invention, a substrate is cut into a substrate shape at a substantially predetermined off angle with a wire saw or the like, and the surface of the substrate is mirror-polished to a predetermined off angle. May be manufactured.

When a GaN-based semiconductor layer is grown on the n-GaN off-substrate 1 in which the off-angle B and the off-direction are set as described above, crystal growth is likely to occur in the GaN-based semiconductor layer in a step flow mode. . For this reason, in the GaN-based semiconductor layer formed on the n-GaN off-substrate 1, dislocations are reduced and good crystallinity is realized.

In particular, when such an n-GaN off-substrate 1 is used, even when the GaN-based semiconductor layer is grown at a temperature lower than a normal growth temperature, Ga
The crystal growth of the N-based semiconductor layer can proceed in a step flow mode. Therefore, even when the GaN-based semiconductor layer is grown at a low temperature, a GaN-based semiconductor layer having good crystallinity can be formed.

In the following, as an embodiment of the present invention, AlGa on an n-GaN off substrate 1 manufactured by the method shown in FIG.
The case where an N layer is grown will be described.

In this embodiment, as shown in FIG. 2A, an AlGaN layer 1 is formed on an n-GaN off substrate 1 by MOVPE (metal organic chemical vapor deposition), for example.
5 is grown (FIG. 2B). In this case, AlGaN
In layer 15, growth proceeds in a step flow mode.

By the way, since the surface diffusion of Al atoms during crystal growth is usually small, for example, flat n-Ga
AlGaN with large Al composition on (0001) plane of N layer
When growing a layer, crystal growth is unlikely to occur in step flow mode.

On the other hand, when the AlGaN layer 15 is grown on the off-surface of the n-GaN off-substrate 1 on which the steps of the atomic order are formed, despite the small surface diffusion of Al atoms in the crystal growth, The AlGaN layer 15 mainly grows in a step flow mode. In particular, in this case, even when the Al composition of the AlGaN layer 15 is increased, the growth can proceed in the step flow mode.

Here, in the step flow mode growth of the AlGaN layer 15 as described above, it is possible to reduce dislocations in the crystal. Therefore, good crystallinity is realized in the AlGaN layer 15 grown on the n-GaN off substrate 1.

In particular, in this case, good crystallinity is realized even in the AlGaN layer 15 having a large Al composition, and generation of cracks is prevented. Therefore, nG
By using the aN-off substrate 15, the AlGaN layer 1
5 can be increased.

In this case, the difference in lattice constant between the n-GaN off substrate 1 and the AlGaN layer 15 is as follows:
The difference in lattice constant between the sapphire substrate and the AlGaN layer is small. Therefore, in the AlGaN layer 15 grown on the n-GaN off-substrate 1, the dislocation generated due to the difference in lattice constant from the substrate is reduced, and better crystallinity is realized.

Further, by using the n-GaN off-substrate 1, the AlGaN layer 15 can be formed at a temperature lower than the substrate temperature during normal AlGaN growth,
In the case where the AlGaN layer 15 is grown, the crystal growth of the AlGaN layer 15 can be performed in the step flow mode. Therefore, even when the AlGaN layer 15 is grown at such a low temperature, good crystallinity can be realized in the AlGaN layer 15.

In the above, the AlGaN layer 15 may be undoped, n-type or p-type.

Here, as described above, since the crystallinity of the AlGaN layer 15 is improved by using the n-GaN off-substrate 1, the activation rate of Mg in the AlGaN layer 15 is increased to reduce the carrier concentration. It becomes possible to raise it. In particular, in this case, p having a large Al composition
-It is possible to increase the carrier concentration also in the AlGaN layer. Therefore, in this case, n-
With the GaN off substrate 1, a greater effect can be obtained.

Next, a nitride-based semiconductor device manufactured by using the n-GaN off-substrate 1 of FIG. 1 will be described.

FIG. 3 is a schematic perspective view showing an example of the nitride-based semiconductor device according to the present invention. In this case, a nitride semiconductor laser device will be described as the nitride semiconductor device according to the present invention.

The semiconductor laser device 100 shown in FIG. 3 is manufactured by the following method. When manufacturing the semiconductor laser device 100, first, as shown in FIG.
A buffer layer 2 and an n-AlG
aN second cladding layer 3, n-GaN first cladding layer 4, MQW light emitting layer 5 having a multiple quantum well (MQW) structure, p-GaN first cladding layer 6, p-AlGaN second cladding layer 6
The cladding layer 7 and the p-GaN cap layer 8 are sequentially grown.

The MQW light emitting layer 5 includes a GaN barrier layer having a thickness of about 4 nm and an In _0.15 Ga _0.85
N well layers are alternately stacked. In this case, GaN
There are five barrier layers, and four In _0.15 Ga _0.85 N well layers.

In FIG. 4A, n-GaN
The off surface of the off-substrate 1 is schematically shown as being horizontal and flat. In this case, the n-GaN off-substrate 1 is shown in FIG.
As shown in [11-2], [11-2]
0] direction. Further, a step of an atomic order is formed on the off plane.

The composition, film thickness, substrate temperature during growth and carrier concentration of each of the layers 2 to 8 are as shown in Table 1.

[0071]

[Table 1]

Each of the above-mentioned layers 2 to 8 is grown by the MOVPE method (metal organic chemical vapor deposition) at atmospheric pressure. In this case, trimethyl aluminum (TM
Al), trimethylgallium (TMGa), trimethylindium (TMIn), NH ₃ , silane gas (SiH
₄ ), cyclopentadienyl magnesium (Cp ₂ M
G) is used.

In this case, since each of the layers 2 to 8 is grown on the n-GaN off-substrate 1, crystal growth mainly occurs in the step flow mode in each of the layers 2 to 8. Therefore, in each of layers 2 to 8, dislocations are reduced and good crystallinity is realized.

In particular, in the above, the use of the n-GaN off-substrate 1 allows the n-AlGaN second cladding layer 3 and the p-AlGaN second cladding layer 3 having a large Al composition and a large thickness to be 0.3. Also in the layer 7, the crystal growth can proceed in the step flow mode. Therefore, good crystallinity is realized also in these layers 3 and 7, and the occurrence of cracks is prevented.

Since the p-AlGaN second cladding layer 7 has good crystallinity as described above, p-AlG
In the aN second cladding layer 7, it is possible to increase the activation rate of Mg to increase the carrier concentration to about 2 × 10 ¹⁸ cm ⁻³ .

Further, in this case, the n-GaN off substrate 1
And the difference between the lattice constants of the layers 2 to 8 is small.
In No. 8, the dislocation generated due to the difference in lattice constant from the substrate is reduced. Therefore, in each of the layers 2 to 8, better crystallinity can be realized.

In the above description, the n-AlGaN second cladding layer 3 and the p-AlGaN second cladding layer 7
Although the substrate temperature at the time of growth is 1150 ° C., these layers 3 and 7 may be grown at a lower temperature, for example, 750 to 950 ° C. Also in this case, n-
AlGaN second cladding layer 3 and p-AlGaN second
Crystal growth in the cladding layer 7 can be performed in a step flow mode. Therefore, even when grown at such a low temperature, good crystallinity can be realized in these layers 3 and 7.

Subsequently, as shown in FIG.
On the entire surface of the aN cap layer 8, for example, a 0.2 μm thick
A current confinement layer 9 made of silicon nitride such as Si ₃ N _{4 having} a thickness of about m is formed. Next, photolithography and BH
Wet etching with F (buffered hydrofluoric acid), width 2μ
The silicon nitride in the stripe-shaped region of about m is removed to expose the p-GaN cap layer 8. Thus, a stripe-shaped current path 10 is formed.

Next, as shown in FIG.
The p-GaN cap layer 8 on the current confinement layer 9 and in the stripe-shaped opening is formed by the reduced pressure MOVPE method of 6 Torr.
The thickness is 3-5 μm and the carrier concentration is 3 × 10 ¹⁸
A p-GaN contact layer 11 made of cm.sup.- ³ Mg-doped GaN is formed. At this time, the p-GaN cap layer 8
The growth conditions are adjusted appropriately so that p-GaN grows selectively on the exposed portions of the. For example, the substrate temperature is increased by about 100 ° C., and the amount of NH ₃ is increased by about three times.

When growth is performed under such conditions, pG
The p-GaN grows on the exposed portion of the aN cap layer 8, and a portion corresponding to the current path 10 is formed. On the other hand, p-GaN does not grow on the current confinement layer 9. When the crystal growth is continued, p-GaN grows on the current path 10 and p-Ga grown on the current path 10 continues.
The crystal growth starts in the lateral direction from the side surface of N and the current confinement layer 9
A p-GaN contact layer 11 made of p-GaN is formed thereon. For example, the p-GaN contact layer 11 is formed with a width of about 8 μm around a portion corresponding to the current path 10.

As a result, the p-GaN cap layer 8 and the p-GaN
The p-GaN cap layer 8 is connected to the GaN contact layer 11 through a stripe-shaped current path 10 having a width of about 2 μm.
Between the current path 10 and the p-GaN contact layer 11.
A current confinement layer 9 made of Si ₃ N ₄ having a thickness of about 0.2 μm is formed except for the portion of.

Further, as shown in FIG.
An n-electrode 51 made of, for example, Au / Ti is formed on a surface (back surface) of the aN-off substrate 1 opposite to the crystal growth surface.
Further, a p-electrode 50 made of Au / Pd is formed on the p-GaN contact layer 11.

Finally, a cavity structure having a cavity length of 300 μm is formed in the direction along the stripe-shaped current path 10 by cleavage, for example. Thereby, the semiconductor laser device 100 is formed.

Incidentally, a high-reflection film or a low-reflection film such as a dielectric multilayer film in which Si ₃ N ₄ , SiO ₂ , Al ₂ O ₃ , TiO ₂ or the like is laminated is formed on the cavity end surface of the semiconductor laser device 100. You may.

In the above-described semiconductor laser device 100, since the n-GaN off-substrate 1 is used, each of the layers 2 to
8 occurs in a step flow mode. For this reason, in each of layers 2 to 8, dislocations are reduced, and good crystallinity is realized.

In this case, the difference between the lattice constant of the n-GaN off-substrate 1 and the lattice constants of the layers 2 to 8 is small. Therefore, in each of the layers 2 to 8, dislocations generated due to a difference in lattice constant from the substrate are reduced. Therefore, better crystallinity is realized in each of the layers 2 to 8.

In particular, in the semiconductor laser device 100, by using the n-GaN off-substrate 1, n-AlGaN having small surface diffusion of Al atoms during crystal growth is used.
Also in the second cladding layer 3 and the p-AlGaN second cladding layer 7, the crystal growth can proceed in the step flow mode. Therefore, n-
AlGaN second cladding layer 3 and p-AlGaN second
The clad layer 7 is obtained.

As a result, the occurrence of hillocks in the second n-AlGaN cladding layer 3 and the second p-AlGaN cladding layer 7 is reduced, and the surface morphology is also improved. As a result, even when the thickness and Al composition of the n-AlGaN second cladding layer 3 and the p-AlGaN second cladding layer 7 are increased as described above, the n-AlG
Good crystallinity is realized in the aN second cladding layer 3 and the p-AlGaN second cladding layer 7, and the occurrence of cracks is prevented.

Since the p-AlGaN second cladding layer 7 has good crystallinity, it is possible to increase the Al composition and the carrier concentration in the p-AlGaN second cladding layer 7.

As described above, the above semiconductor laser device 1
In 00, by using the n-GaN substrate 1,
n-AlGaN second cladding layer 3 and p-AlGaN
The Al composition and the film thickness of the second cladding layer 7 can be increased and the occurrence of cracks can be prevented. For this reason, it is possible to effectively confine light and obtain a good vertical far-field image.

As described above, by using the n-GaN off-substrate 1, better crystallinity can be realized in each of the layers 2 to 8 of the semiconductor laser device 100 than when using a sapphire substrate. Therefore, it is possible to improve the element characteristics.

In the above description, n-
Although the GaN off-substrate 1 is used, the material of the off-substrate is G
It is not limited to aN. As a material for such an off-substrate, a hexagonal nitride-based semiconductor such as AlGaN can be used.

The material of the light emitting layer is not limited to the above, but may be an InGaN single layer, InGaN / AlGaN
Quantum well structure, GaN / AlGaN quantum well structure, Al
It may be a GaN single layer or the like. In this case, the same effect as above can be obtained.

In particular, when the light emitting layer has an InGaN / AlGaN quantum well structure, a GaN / AlGaN quantum well structure,
When a material having a short emission wavelength such as an aN single layer is used, it is necessary to form a clad layer having a high Al composition in order to effectively confine carriers in the light emitting layer.
Therefore, in such a case, the effect of preventing the occurrence of cracks according to the present invention is remarkable.

In the above description, the material of the n-type second cladding layer and the p-type first cladding layer is not limited to AlGaN, but AlGaBN, AlBN, ABN.
With 1BInGaN or the like, the same effects as above can be obtained.

The materials of the layers other than the n-type second clad layer and the p-type first clad layer are not limited to the above-mentioned materials. Each layer may be made of a group III nitride semiconductor.

In the above description, a semiconductor laser device has been described as a semiconductor device according to the present invention. However, the present invention is also applicable to semiconductor devices other than the semiconductor laser device, that is, light emitting diode devices, waveguide device transistors, light receiving devices and the like. It is possible. This case will be described below.

FIG. 7 is a schematic sectional view showing another example of the semiconductor device according to the present invention. In this case, a light receiving element will be described as a semiconductor element.

Although the off surface of the n-GaN off substrate 1 is schematically shown in FIG. 7 as being horizontal and flat, the n-GaN off substrate 1 in this case is as shown in FIG. Has an off-plane that is off by 15 ° in the [11-20] direction from the (0001) plane of GaN. Further, a step of an atomic order is formed on the off plane.

As shown in FIG. 7, the light receiving element 101 has n
An n-buffer layer 21 made of Si-doped GaN having a thickness of about 4 μm on a GaN off substrate 1 and a first n- buffer layer made of Si-doped Al _0.4 Ga _0.6 N having a thickness of about 1 μm;
AlGaN layer 22, second n-AlGaN layer 2 made of Si-doped Al _0.4 Ga _0.6 N having a thickness of about 0.1 μm
3. High resistance AlGaN film 2 made of Al _0.35 Ga _0.65 N
4. Mg-doped Al _0.35 Ga with a film thickness of about 0.1 μm
_A p-AlGaN layer 25 made of _0.65 N and a film thickness of 0.
A p-GaN contact layer 26 made of Mg-doped GaN of about 05 μm is laminated in order.

In this case, the carrier concentration of each of the layers 21 to 23, 25, 26 is 1 × 10 ¹⁸ cm ⁻³ , 1 × 10 ¹⁸ c
m ⁻³ , 1 × 10 ¹⁷ cm ⁻³ , 1 × 10 ¹⁷ cm ⁻³ and 1 ×
It is 10 ¹⁸ cm ^-3 .

In the light receiving element 101, the first nA
lGaN layer 22, second n-AlGaN layer 23, high-resistance AlGaN film 24, p-AlGaN layer 25, and p-G
The aN contact layer 26 forms the light receiving section PR.

Here, when the light receiving element 101 is a PIN type light receiving element, the high resistance AlGaN film 2
4 has a thickness of 0.1 μm.

On the other hand, when the light receiving element 101 is an APD (avalanche photodiode),
The thickness of the high-resistance AlGaN film 24 is increased in order to prevent the electric field intensity in the film from being excessively increased when a high voltage is applied. However, if the thickness of the high-resistance AlGaN film 24 is too large, the automatic speed of the light receiving element 101 decreases. Therefore, the thickness of the high-resistance AlGaN film 24 in this case is set to a thickness at which a sufficient automatic speed can be realized in practical use, for example, about 0.5 μm.

On the surface (back surface) opposite to the crystal growth surface of the n-GaN off substrate 1, an n-electrode 32 having a two-layer structure formed by laminating a Ti film and an Al film in this order from the substrate side is formed. ing. In addition, on the p-GaN contact layer 26, N
i-layer and Au film in this order, a two-layer p-layer
An electrode 31 is formed. Further, the first n-AlG
From the aN layer 22 to the periphery of the p-GaN contact layer 26,
A high resistance region HR is formed.

In order to form the high resistance region HR, at the time of manufacturing the light receiving element 101, a resistance increasing process is performed by ion implantation using hydrogen ions. Hereinafter, a method for forming the high-resistance region HR will be described with reference to FIG.

FIG. 8 is a top view of a semiconductor wafer having the layers 21 to 26 formed on the n-GaN off-substrate 1. A chain line A in FIG. 8 indicates an element isolation line. That is, the area defined by the chain line A corresponds to each element formation area.

As shown in FIG. 8, hydrogen ions are implanted into the region 30 of the semiconductor wafer indicated by oblique lines in the thickness direction of the wafer. In this case, the depth at which the hydrogen ions are implanted is a depth that reaches the first n-AlGaN layer 22. Thereafter, a p-electrode 31 is formed in a region where hydrogen ions have not been implanted.

When forming the p-electrode 31 and the n-electrode 32, the respective films constituting the p-electrode 31 and the n-electrode 32 are laminated in the above-mentioned order by, for example, EB vapor deposition or various sputter vapor depositions. Further, the p-electrode 31 is formed in a ring shape by a lift-off method, chemical etching, or the like. After forming the p-electrode 31 and the n-electrode 32 in this manner, the light-receiving elements 101 are separated along the chain line A. Note that a heat treatment may be performed after the formation of the p-electrode 31 and the n-electrode 32 as necessary.

In the light receiving element 101, nG
Since the aN-off substrate 1 is used, each layer 2 of the light receiving portion PR
Crystal growth of 1-26 occurs mainly in step flow mode. For this reason, in each of the layers 21 to 26 of the light receiving portion, dislocations are reduced, and good crystallinity is realized, and generation of cracks is prevented.

In particular, in such a light receiving element 101, the first n-AlGaN layer 22, the second n-AlGaN layer 23, and the high-resistance AlGaN
In the film 24 and the p-AlGaN layer 25, the crystal growth can proceed in the step flow mode despite the small surface of Al atoms in the crystal growth. Therefore, in these layers 22 to 25, good crystallinity is realized.

Thus, each layer 22 to 25 of the light receiving portion PR
In, the generation of hillocks is reduced, and the surface morphology is also improved. As a result, in each of the layers 22 to 25 of the light receiving unit PR made of AlGaN, it is possible to increase the film thickness and the Al composition while preventing the occurrence of cracks.

Further, as described above, the p-AlGaN layer 2
5 has good crystallinity, so that in the p-AlGaN layer 25, it is possible to increase the Al composition and the carrier concentration.

As described above, in the light receiving element 101, the A of the light receiving section PR is prevented while preventing the occurrence of cracks.
It is possible to increase the Al composition and the film thickness of the lGaN layers 22 to 25. Therefore, it is possible to realize a light receiving element having high sensitivity to light having a short wavelength.

In this case, since the lattice constant of the n-GaN off-substrate 1 is close to the lattice constant of each of the layers 21 to 26, the layers 21 to 26 are generated due to the difference in lattice constant from the substrate. Dislocations are reduced. Thereby, better crystallinity is realized in each of the layers 21 to 26. Therefore, the element characteristics of the light receiving element 101 are improved.

In the semiconductor laser device 100 of FIG. 3 and the light receiving device 101 of FIG. 7, the n-type layer is formed first on the substrate, but the p-type layer may be formed on the substrate first. .

Each layer of the semiconductor laser device 100 of FIG. 3 and the light receiving device 101 of FIG. 7 can be grown by a crystal growth method other than the above. For example, HVPE method, T
MAl, TMGa, TMIn, NH ₃ , SiH ₄ , Cp
_It can also be grown by a gas source MBE method using ₂ Mg as a source gas.

[0118]

(Example 1) In Example 1, n-GaN off-substrates 1 having different off-angles in the range of 1 to 20 ° were produced by the method shown in FIG. Next, FIG.
As shown in FIG. 2, a 2 μm thick AlGaN made of undoped Al _0.3 Ga _0.7 N is formed on each n-GaN off-substrate 1.
The layer 15 was grown, and the dislocation density of the AlGaN layer 15 was measured.

The off-direction of the n-GaN off-substrate 1 in Example 1 was the [11-20] direction. Here, the substrate temperature during the growth of the AlGaN layer 15 is set to 1150.
° C and when the substrate temperature during growth of the AlGaN layer 15 was 950 ° C.
The dislocation density of No. 5 was measured.

Table 2 and FIG. 9 show the measurement results of the dislocation density of the AlGaN layer 15 in Example 1.

[0121]

[Table 2]

As shown in Table 2 and FIG.
When the substrate temperature during the growth of the layer 15 is 1150 ° C., n-G
When the off angle of the aN off substrate 1 is in the range of 1 to 20 °, A
The dislocation density of the lGaN layer 15 is 6 × 10⁸cm^-2(6 μm
^-2) Below. In addition, the base during the growth of the AlGaN layer 15
When the plate temperature is 950 ° C., the n-GaN off substrate 1 is turned off.
When the angle is in the range of 1 to 20 °, dislocation of the AlGaN layer 15 is caused.
Density is 1 × 10⁹cm ^-2(10 μm^-2) Below.

On the other hand, in any case where the substrate temperature at the time of growth of the AlGaN layer 15 is 1150 ° C. or 950 ° C., if the off-angle is less than 1 ° or more than 20 °, the dislocation density of the AlGaN layer 15 becomes lower. To increase.

As described above, by using the n-GaN off-substrate 1 having an off-angle in the range of 1 to 20 °, the Al-Al substrate can be formed even when the substrate temperature during growth is 1150 ° C. or 950 ° C. Al with composition as large as 0.3
It was found that good crystallinity was obtained in the GaN layer 15.

(Embodiment 2) In the embodiment 2, according to the method shown in FIG.
0] from the direction 0 to 30 °.
A GaN off substrate 1 was produced. Next, as shown in FIG. 2, undoped Al _0.3
An AlGaN layer 15 of Ga _0.7 N having a thickness of 2 μm was grown, and the dislocation density of the AlGaN layer 15 was measured.

In the second embodiment, the off angle is 1
° n-GaN off-substrate 1 was prepared, and n-GaN off-substrate 1 having an off-angle of 2 ° was prepared. In each case, the dislocation density of AlGaN layer 15 was measured.
In this case, the substrate temperature during growth of the AlGaN layer 15 was 1150 ° C.

Table 3 and FIG. 10 show the measurement results of the dislocation density of the AlGaN layer 15 in Example 2.

[0128]

[Table 3]

The off direction (°) shown on the horizontal axis in FIG.
Indicates how many degrees (°) the off direction of the n-GaN off substrate 1 is shifted from the [11-20] direction in the substrate plane. In this case, the 0 ° off direction is [11
−20] direction. The 30 ° off direction corresponds to the [01-10] direction.

As shown in Table 3 and FIG. 10, n-Ga
In both cases of the off-angles of the N-off substrate of 1 ° and 2 °, the off-direction of the substrate is ± 7 from the [11-20] direction.
°, the AlGaN layer 15
Has the best crystallinity.

On the other hand, when the off direction of the substrate is [11-2]
If the direction is more than ± 7 ° from the [0] direction, the dislocation density of the AlGaN layer 15 increases.

From the above, the off direction is [11-20].
By using the n-GaN off-substrate 1 in a direction within a range of ± 7 ° from the direction, the Al composition having a large Al composition of 0.3 at any of the off-angles of 1 ° and 2 °.
It was found that good crystallinity was obtained in the lGaN layer 15.

[Brief description of the drawings]

FIG. 1 is a schematic process sectional view showing an example of a method for manufacturing a nitride-based semiconductor substrate according to the present invention.

2 is a schematic process sectional view showing an example using the nitride semiconductor substrate of FIG. 1;

FIG. 3 is a schematic perspective view of a nitride-based semiconductor device according to the present invention.

FIG. 4 is a schematic process sectional view illustrating the method for manufacturing the nitride-based semiconductor device of FIG.

FIG. 5 is a schematic step-by-step cross-sectional view illustrating the method for manufacturing the nitride-based semiconductor device of FIG.

6 is a schematic process sectional view showing the method for manufacturing the nitride-based semiconductor device of FIG.

FIG. 7 is a schematic sectional view showing another example of the nitride semiconductor device according to the present invention.

FIG. 8 is a schematic plan view showing a method for manufacturing the light receiving element of FIG.

FIG. 9 is a diagram showing the results of Example 1.

FIG. 10 is a diagram showing the results of Example 2.

FIG. 11 is a schematic sectional view showing a conventional semiconductor laser device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 n-GaN off substrate 2, 21 n-buffer layer 3 n-second cladding layer 4 n-first cladding layer 5 MQW light emitting layer 6 p-first cladding layer 7 p-second cladding layer 8 p-cap layer Reference Signs List 9 current constriction layer 10 current path 11 p-contact layer 22 first n-AlGaN layer 23 second n-AlGaN layer 24 high-resistance AlGaN film 25 p-AlGaN layer 26 p-GaN contact layer 50 p electrode 51 n electrode 100 semiconductor laser element 101 light receiving element

Continued on the front page F-term (reference) 5F041 AA40 CA23 CA34 CA40 CA64 CA66 5F045 AA04 AB14 AB17 AC01 AC08 AC12 AC19 AD12 AD13 AD15 AF04 AF13 BB12 CA10 CA12 CA13 DA53 DA55 GH02 5F049 MA03 MA04 MA07 MB07 PA03 SS04 5F073 AA09A EA29

Claims (9)

[Claims] 1. A nitride-based semiconductor substrate comprising a hexagonal nitride-based semiconductor, comprising: an inclined surface inclined at a predetermined angle from a (0001) plane in a predetermined direction; Is not less than 1 degree and not more than 20 degrees. 2. The inclination direction of the inclined surface is a direction within a range of 0 ° to 7 ° from a <11-20> direction in a substrate plane, or a direction equivalent thereto. The nitride-based semiconductor substrate according to claim 1, wherein 3. The nitride semiconductor substrate according to claim 1, wherein said nitride semiconductor substrate is made of GaN. 4. A nitride-based semiconductor device comprising at least one nitride-based semiconductor layer formed on a nitride-based semiconductor substrate made of a hexagonal nitride-based semiconductor, wherein the nitride-based semiconductor The substrate has an inclined surface inclined at a predetermined angle from the (0001) plane in a predetermined direction, and the inclination angle of the inclined surface is 1
A nitride semiconductor device, wherein the temperature is not less than 20 degrees and not more than 20 degrees. 5. The inclination direction of the inclined surface of the nitride-based semiconductor substrate is 0 from the <11-20> direction in the substrate plane.
5. The nitride-based semiconductor device according to claim 4, wherein the direction is in a range of not less than 7 degrees and not more than 7 degrees. 6. The nitride semiconductor device according to claim 4, wherein said nitride semiconductor substrate is made of GaN. 7. The nitride semiconductor layer according to claim 4, wherein a first nitride semiconductor layer, an active element region, and a second nitride semiconductor layer are formed in this order.
7. The nitride-based semiconductor device according to any one of items 6 to 6. 8. The method according to claim 1, wherein the first nitride-based semiconductor layer includes a nitride-based semiconductor layer including Al, and the second nitride-based semiconductor layer includes a nitride-based semiconductor layer including Al. The nitride-based semiconductor device according to claim 7, wherein 9. The method according to claim 1, wherein the first nitride-based semiconductor layer containing Al and the second nitride-based semiconductor layer containing Al in the second nitride-based semiconductor layer are made of AlGaN. The nitride semiconductor device according to claim 8, wherein