JP2013089616A - Crystalline laminate structure and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a crystalline laminate structure in which a dislocation density of a top face of a nitride semiconductor layer on a GaOsubstrate is low, and to provide a manufacturing method thereof.SOLUTION: In one embodiment, a crystalline laminate structure 1 comprises: a GaOsubstrate 2; a buffer layer 3 which is arranged on the GaOsubstrate 2 and is made of an AlGaInN(0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1) crystal; and a nitride semiconductor layer 4 which is arranged on the buffer layer 3 and is made of an AlGaInN(0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1) crystal containing oxygen as an impurity. A region 4a with a thickness of 200 nm or more, which is on the GaOsubstrate 2 side of the nitride semiconductor layer 4, has an oxygen concentration of 1.0×10/cmor more.

Description

  The present invention relates to a crystal multilayer structure and a method for manufacturing the same.

2. Description of the Related Art Conventionally, an LED element including a crystal laminated structure including a Ga ₂ O ₃ substrate, an AlN buffer layer, and a GaN layer is known (see, for example, Patent Document 1). According to Patent Document 1, the GaN layer is formed by growing a GaN crystal on the AlN buffer layer under a temperature condition of 1050 ° C.

JP 2006-310765 A

  However, according to the method described in Patent Document 1, since the GaN crystal is grown at a high temperature of 1050 ° C., the oxygen concentration of the GaN layer is lowered. Therefore, the dislocation density on the upper surface of the GaN layer (the surface opposite to the AlN buffer layer) is increased, and a leakage current is generated in the low voltage region when a vertical voltage is applied to the element including the crystal multilayer structure. .

Accordingly, an object of the present invention is to provide a crystal laminated structure having a low dislocation density on the upper surface of a nitride semiconductor layer on a Ga ₂ O ₃ substrate, and a method for manufacturing the same.

  In order to achieve the above object, one embodiment of the present invention provides a crystal laminate structure according to [1] to [6] and a method for producing a crystal laminate structure according to [7] to [10].

[1] From a Ga ₂ O ₃ substrate and an Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal on the Ga ₂ O ₃ substrate. And a nitride layer made of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) containing oxygen as an impurity on the buffer layer. A crystal laminated structure, wherein an oxygen concentration in a region having a thickness of 200 nm or more on the Ga ₂ O ₃ substrate side of the nitride semiconductor layer is 1.0 × 10 ¹⁸ / cm ³ or more. .

[2] The crystal multilayer structure according to [1], wherein a dislocation density on the surface of the nitride semiconductor layer opposite to the Ga ₂ O ₃ substrate is less than 1.0 × 10 ⁹ / cm ^2.

[3] In the above [1] or [2], an oxygen concentration of a region having a thickness of 500 nm or more on the Ga ₂ O ₃ substrate side of the nitride semiconductor layer is 1.0 × 10 ¹⁸ / cm ³ or more. The crystal laminated structure described.

[4] The crystal multilayer structure according to any one of [1] to [3], wherein the oxygen concentration in the region is 5.0 × 10 ¹⁸ / cm ³ or more.

[5] The crystal stacked structure according to any one of [1] to [4], wherein the Al _x Ga _y In _z N crystal of the buffer layer is an AlN crystal.

[6] The crystal stacked structure according to any one of [1] to [5], wherein the Al _x Ga _y In _z N crystal of the nitride semiconductor layer is a GaN crystal.

[7] A first Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal is grown on a Ga ₂ O ₃ substrate to form a buffer layer. And growing a second Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal on the buffer layer Forming the nitride semiconductor layer, and first growing the second Al _x Ga _y In _z N crystal at a first temperature of 1000 ° C. or lower, Thereafter, the second at a second temperature higher than the first temperature _Al x _Ga y in _z N was grown crystal, the second _Al x growing in the first temperature _Ga y _in z N A method for producing a crystal laminated structure, wherein the crystal thickness is 200 nm or more.

[8] The method for producing a crystal stacked structure according to [7], wherein the thickness of the second Al _x Ga _y In _z N crystal grown at the first temperature is 500 nm or more.

[9] The method for producing a crystal stacked structure according to [7] or [8], wherein the first Al _x Ga _y In _z N crystal is an AlN crystal.

[10] The method for manufacturing a crystal stacked structure according to any one of [7] to [9], wherein the second Al _x Ga _y In _z N crystal is a GaN crystal.

According to the present invention, it is possible to provide Ga ₂ O ₃ dislocation density of the upper surface of the nitride semiconductor layer on the substrate is low crystalline layered structure, and a manufacturing method thereof.

FIG. 1 is a cross-sectional view of a crystal multilayer structure according to an embodiment. FIG. 2 is a graph showing an example of a manufacturing process sequence of the crystal laminated structure according to the embodiment. FIG. 3 shows the relationship between the thickness of the high oxygen concentration layer and the dislocation density on the top surface of the nitride semiconductor layer according to Example 1, and the relationship between the oxygen concentration in the high oxygen concentration layer and the dislocation density on the top surface of the nitride semiconductor layer. It is a graph which shows. FIG. 4 is a cross-sectional view of the LED element according to the second embodiment.

Embodiment
(Structure of crystal laminated structure)
FIG. 1 is a cross-sectional view of a crystal multilayer structure 1 according to an embodiment. The crystal stacked structure 1 includes a Ga ₂ O ₃ substrate 2, a buffer layer 3 on the Ga ₂ O ₃ substrate 2, and a nitride semiconductor layer 4 on the buffer layer 3.

The Ga ₂ O ₃ substrate 2 is made of a β-Ga ₂ O ₃ single crystal.

The buffer layer 3 is made of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal. Further, in order to successfully form a high oxygen concentration layer 4a of the nitride semiconductor layer 4 to be described later, the coverage of the upper surface of the Ga ₂ O ₃ substrate 2 of the buffer layer 3 is preferably 10 to 90%, For example, the buffer layer 3 is formed in an island shape as shown in FIG.

The buffer layer 3 is preferably made of an AlN crystal (x = 1, y = z = 0), among Al _x Ga _y In _z N crystals. When the buffer layer 3 is made of an AlN crystal, the adhesion between the Ga ₂ O ₃ substrate 2 and the nitride semiconductor layer 4 is further increased.

The nitride semiconductor layer 4 includes a high oxygen concentration layer 4a in contact with the buffer layer 3 and a low oxygen concentration layer 4b on the high oxygen concentration layer 4a. The nitride semiconductor layer 4 (high oxygen concentration layer 4a and low oxygen concentration layer 4b) is made of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) containing oxygen as an impurity. , X + y + z = 1) crystal, particularly preferably a GaN crystal (y = 1, x = z = 0) with good crystal quality. The thickness of the nitride semiconductor layer 4 is 3 μm, for example.

The dislocation density on the upper surface of the nitride semiconductor layer 4 (the surface opposite to the Ga ₂ O ₃ substrate 2), that is, the upper surface of the low oxygen concentration layer 4b is low, and a vertical voltage is applied to the element including the crystal multilayer structure 1 As a result, the occurrence of leakage current in the low voltage region can be suppressed. In particular, when the dislocation density on the upper surface of the low oxygen concentration layer 4b is less than 1.0 × 10 ⁹ / cm ² , the above leakage current can be suppressed to a practical level.

The high oxygen concentration layer 4a has an oxygen concentration higher than that of the low oxygen concentration layer 4b and has an oxygen concentration of 1.0 × 10 ¹⁸ / cm ³ or more. The thickness of the high oxygen concentration layer 4a is 200 nm or more. By providing the high oxygen concentration layer 4a, the dislocation density on the upper surface of the nitride semiconductor layer 4 is reduced.

In order to further reduce the dislocation density on the upper surface of the nitride semiconductor layer 4, the oxygen concentration of the high oxygen concentration layer 4a is preferably 5.0 × 10 ¹⁸ / cm ³ or more, and the high oxygen concentration layer 4a The thickness is preferably 500 nm or more.

  Since the semiconductor crystal needs to be finally grown at a high temperature so as not to form pits (holes) on the surface of nitride semiconductor layer 4, low oxygen concentration layer 4b having a relatively low oxygen concentration is formed.

The Ga ₂ O ₃ substrate 2 and the nitride semiconductor layer 4 (the high oxygen concentration layer 4a and the low oxygen concentration layer 4b) may include a conductive impurity such as Si.

(Method for producing crystal laminated structure)
FIG. 2 is a graph showing an example of the manufacturing process sequence of the crystal laminated structure according to the present embodiment. The broken line in FIG. 2 represents a change in temperature condition with the passage of time.

First, using phosphoric acid heated concentration 98 wt% to 0.99 ° C., subjected to a pretreatment _Ga 2 _{O 3} substrate 2 to 120 minutes. By this pretreatment, the surface of the Ga ₂ O ₃ substrate 2 is etched by about 1000 nm.

Next, after transporting the Ga ₂ O ₃ substrate 2 into the chamber of a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, the temperature in the chamber is raised to T1 (step S1). Here, T1 is 350-600 degreeC, for example, is 450 degreeC.

Next, NH ₃ gas as a raw material of N, trimethyl gallium (TMG) as a raw material of Ga, trimethyl aluminum (TMA) as a raw material of Al, and a raw material of In with the temperature in the chamber maintained at T1 Then, trimethylindium (TMI) is supplied into the chamber, and an Al _x Ga _y In _z N crystal is grown on the Ga ₂ O ₃ substrate 2 to form the buffer layer 3 (step S2).

  Next, the temperature in the chamber is raised to T2 (step S3). Here, T2 is 1000 ° C. or less, for example, 950 ° C. When T2 exceeds 1000 ° C., the oxygen concentration of the high oxygen concentration layer 4a is likely to decrease.

Next, with the temperature in the chamber maintained at T2, NH ₃ , TMG, TMA, and TMI are supplied into the chamber, and an Al _x Ga _y In _z N crystal is grown on the buffer layer 3 to be nitrided. The high oxygen concentration layer 4a of the physical semiconductor layer 4 is formed (step S4).

  Next, the temperature in the chamber is raised to T3 while continuing to supply each source gas (step S5). Here, T3 is higher than T2 and preferably higher than 1000 ° C., for example, 1050 ° C.

Next, the growth of the Al _x Ga _y In _z N crystal is continued with the temperature in the chamber kept at T3, and the low oxygen concentration layer 4b of the nitride semiconductor layer 4 is formed (step S6). Thereby, the crystal laminated structure 1 is obtained.

  Thereafter, the temperature in the chamber is lowered (step S7), and the crystal laminated structure 1 is taken out from the chamber.

(Effect of embodiment)
According to the present embodiment, by providing a region having a high oxygen concentration on the Ga ₂ O ₃ substrate side of the nitride semiconductor layer, a crystal stacked structure having a low dislocation density on the top surface of the nitride semiconductor layer can be formed. it can. For this reason, when forming elements, such as an LED element, using a crystal | crystallization laminated structure, generation | occurrence | production of the leakage current in a low voltage area | region can be suppressed.

  In Example 1, the relationship between the thickness of the high oxygen concentration layer 4a and the dislocation density of the upper surface of the nitride semiconductor layer 4 in the crystal multilayer structure 1 of the embodiment, and the oxygen concentration of the high oxygen concentration layer 4a and the nitride semiconductor The relationship with the dislocation density on the upper surface of the layer 4 was evaluated.

Twelve crystal laminated structures having different oxygen concentrations and thicknesses of the high oxygen concentration layer corresponding to the high oxygen concentration layer 4a were prepared and evaluated. Here, the oxygen concentration of the high oxygen concentration layer is 1.0 × 10 ¹⁷ / cm ³ , 1.0 × 10 ¹⁸ / cm ³ , or 5.0 × 10 ¹⁸ / cm ³ , and the thickness is 100 nm. , 200 nm, 500 nm, or 1000 nm. Among these, the high oxygen concentration layer having an oxygen concentration of 1.0 × 10 ¹⁸ / cm ³ or more and a thickness of 200 nm or more corresponds to the high oxygen concentration layer 4a of the embodiment of the present invention.

Note that the high oxygen concentration layers having oxygen concentrations of 1.0 × 10 ¹⁷ / cm ³ , 1.0 × 10 ¹⁸ / cm ³ , and 5.0 × 10 ¹⁸ / cm ³ have T2 = 1050 ° C. and 1000 ° C., respectively. , And T2 = 950 ° C.

  In any of the crystal stacked structures of this example, the buffer layer corresponding to the buffer layer 3 is an AlN crystal film having a thickness of 5 nm formed under a temperature condition of T1 = 450 ° C., and a high oxygen concentration layer and The low oxygen concentration layer corresponding to the low oxygen concentration layer 4b is a GaN crystal film containing Si, and the thickness of the nitride semiconductor layer corresponding to the nitride semiconductor layer 4 (the thickness of the high oxygen concentration layer and the low oxygen concentration layer). The total thickness was 3 μm, and the low oxygen concentration layer was formed under the temperature condition of T3 = 1050 ° C.

  FIG. 3 is a graph showing the relationship between the thickness of the high oxygen concentration layer and the dislocation density on the top surface of the nitride semiconductor layer, and the relationship between the oxygen concentration in the high oxygen concentration layer and the dislocation density on the top surface of the nitride semiconductor layer. . The vertical axis in FIG. 3 represents the dislocation density [/ cm] on the upper surface of the nitride semiconductor layer, and the horizontal axis represents the thickness [nm] of the high oxygen concentration layer.

3 represents the measured value of the crystal laminated structure in which the oxygen concentration of the high oxygen concentration layer is 1.0 × 10 ¹⁷ / cm ³ , and ◇ indicates the oxygen concentration of the high oxygen concentration layer is 1.0 × is 10 ¹⁸ / cm ³ represents the measure of the crystal multilayer structure, ◆ represents the measured value of the crystalline layered structure of oxygen concentration in the high oxygen concentration layer is 5.0 × ¹⁰ 18 / cm ^3.

As shown in FIG. 3, the higher the oxygen concentration in the high oxygen concentration layer, the lower the dislocation density on the upper surface of the nitride semiconductor layer. Further, the greater the thickness of the high oxygen concentration layer, the lower the dislocation density on the upper surface of the nitride semiconductor layer. In particular, when the oxygen concentration of the high oxygen concentration layer is 1.0 × 10 ¹⁸ / cm ³ or more and the thickness is 200 nm or more, that is, when the high oxygen concentration layer corresponds to the high oxygen concentration layer 4a. Dislocation density on the upper surface of the semiconductor layer is less than 1.0 × 10 ⁹ / cm ^2, and it is effective in generating a leakage current in a low voltage region when a vertical voltage is applied to an element including the crystal stacked structure. Can be suppressed.

  In Example 2, the magnitude of the leakage current in the low voltage region when a voltage in the vertical direction was applied to the LED element formed using the crystal multilayer structure 1 of the embodiment was evaluated.

(Structure of LED element)
FIG. 4 is a cross-sectional view of an LED element formed using the crystal laminated structure according to the embodiment. The LED element 100 includes a Ga ₂ O ₃ substrate 12, a buffer layer 13 on the Ga ₂ O ₃ substrate 12, an n-GaN layer 14 on the buffer layer 13, a light emitting layer 15 on the n-GaN layer 14, The p-GaN layer 16 on the light emitting layer 15, the contact layer 17 on the p-GaN layer 16, the p-type electrode 18 on the contact layer 17, and the surface of the Ga ₂ O ₃ substrate 12 opposite to the buffer layer 13. And the upper n-type electrode 19.

The LED element 100 is a light emitting element having a light extraction surface on the Ga ₂ O ₃ substrate 12 side. The laminate composed of the n-GaN layer 14, the light emitting layer 15, the p-GaN layer 16, and the contact layer 17 has a mesa shape, and its side surface is covered with the SiO ₂ film 20.

Here, the Ga ₂ O ₃ substrate 12, the buffer layer 13, and the n-GaN layer 14 correspond to the Ga ₂ O ₃ substrate 2, the buffer layer 3, and the nitride semiconductor layer 4 of the embodiment, and Ga ₂ O A stacked body of the _three substrates 2, the buffer layer 13, and the n-GaN layer 14 corresponds to the crystal stacked structure 1 of the embodiment.

  The n-GaN layer 14 includes a high oxygen concentration layer 14a and a low oxygen concentration layer 14b. The high oxygen concentration layer 14a and the low oxygen concentration layer 14b correspond to the high oxygen concentration layer 4a and the low oxygen concentration layer 4b of the embodiment, respectively.

The Ga ₂ O ₃ substrate 12 is an n-type β-Ga ₂ O ₃ substrate containing Si. The thickness of the Ga ₂ O ₃ substrate 12 is 400 μm, and the plane orientation of the main surface is (101).

  The buffer layer 13 is an AlN crystal film having a thickness of 5 nm formed at a growth temperature of 450 ° C.

The high oxygen concentration layer 14a is an n-type GaN crystal film containing Si formed at a growth temperature of 950 ° C. The high oxygen concentration layer 14a includes a lower region having a Si concentration of 2.0 × 10 ¹⁹ / cm ^{3 and} a thickness of 10 nm, and an upper region having a Si concentration of 5.0 × 10 ¹⁸ / cm ^{3 and} a thickness of 1000 nm. Note that monomethylsilane gas gas was used as a raw material for Si.

The low oxygen concentration layer 14b is an n-type GaN crystal film having a thickness of 3 μm and formed at a growth temperature of 1050 ° C. The low oxygen concentration layer 14b contains Si having a concentration of 1.0 × 10 ¹⁸ / cm ³ .

  The light emitting layer 15 is composed of a three-layer multiple quantum well structure formed at a growth temperature of 750 ° C. and a GaN crystal film having a thickness of 10 nm thereon. Each multiple quantum well structure is composed of an 8 nm GaN crystal film and a 2 nm thick InGaN crystal film.

The p-GaN layer 16 is a 150-nm-thick p-type GaN crystal film formed at a growth temperature of 1000 ° C. The p-GaN layer 16 contains Mg having a concentration of 5.0 × 10 ¹⁹ / cm ³ . Note that cyclopentadienyl magnesium gas was used as a raw material for Mg.

The contact layer 17 is a 10-nm-thick p-type GaN crystal film formed at a growth temperature of 1000 ° C. The contact layer 17 contains Mg having a concentration of 1.5 × 10 ²⁰ / cm ³ .

  As a comparative example, an LED element using an n-type GaN crystal film having a thickness of 3 μm formed at a growth temperature of 1050 ° C. instead of the high oxygen concentration layer 14a was prepared. This GaN crystal film contains Si having the same concentration as that of the high oxygen concentration layer 14 a of the LED element 100.

(Evaluation of LED elements)
The LED element 100 and the LED of the comparative example were each mounted on a can-type stem using Ag paste, and the current value when a voltage of 2.0 V was applied between the electrodes was measured.

  As a result, the current value in the LED of the comparative example was 20 μA, whereas the current value in the LED element 100 was 0.35 μA. From this result, it was confirmed that the generation of leakage current in the low voltage region is suppressed in the LED element 100.

  While the embodiments and examples of the present invention have been described above, the embodiments and examples described above do not limit the invention according to the claims. It should be noted that not all combinations of features described in the embodiments and examples are necessarily essential to the means for solving the problems of the invention.

1 ... crystalline layered structure, 2 ... _Ga 2 _{O 3} substrate, 3 ... buffer layer, 4 ... nitride semiconductor layer, 4a ... high oxygen concentration layer, 4b ... low oxygen concentration layer

Claims (10)

A Ga ₂ O ₃ substrate;
A buffer layer made of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal on the Ga ₂ O ₃ substrate;
A nitride semiconductor layer made of Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal containing oxygen as an impurity on the buffer layer;
Including
The oxygen concentration of a region having a thickness of 200 nm or more on the Ga ₂ O ₃ substrate side of the nitride semiconductor layer is 1.0 × 10 ¹⁸ / cm ³ or more;
Crystal laminated structure. The dislocation density on the surface of the nitride semiconductor layer opposite to the Ga ₂ O ₃ substrate is less than 1.0 × 10 ⁹ / cm ² .
The crystal laminated structure according to claim 1. The oxygen concentration of a region having a thickness of 500 nm or more on the Ga ₂ O ₃ substrate side of the nitride semiconductor layer is 1.0 × 10 ¹⁸ / cm ³ or more;
The crystal laminated structure according to claim 1 or 2. The oxygen concentration in the region is 5.0 × 10 ¹⁸ / cm ³ or more,
The crystal laminated structure according to any one of claims 1 to 3. The Al _x Ga _y In _z N crystal of the buffer layer is an AlN crystal,
The crystal laminated structure according to any one of claims 1 to 4. The Al _x Ga _y In _z N crystal of the nitride semiconductor layer is a GaN crystal.
The crystal laminated structure according to any one of claims 1 to 5. A buffer layer is formed by growing a first Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal on a Ga ₂ O ₃ substrate. Process,
A second Al _x Ga _y In _z N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, x + y + z = 1) crystal is grown on the buffer layer to form a nitride semiconductor layer. Process,
Including
In the step of forming the nitride semiconductor layer, first, the second Al _x Ga _y In _z N crystal is grown at a first temperature of 1000 ° C. or lower, and then a second temperature higher than the first temperature. Growing the second Al _x Ga _y In _z N crystal at a temperature of
The second Al _x Ga _y In _z N crystal grown at the first temperature has a thickness of 200 nm or more;
Manufacturing method of crystal laminated structure. The thickness of the second Al _x Ga _y In _z N crystal grown at the first temperature is 500 nm or more;
The manufacturing method of the crystal laminated structure of Claim 7. The first Al _x Ga _y In _z N crystal is an AlN crystal;
The manufacturing method of the crystal laminated structure of Claim 7 or 8. The second Al _x Ga _y In _z N crystal is a GaN crystal.
The manufacturing method of the crystal laminated structure as described in any one of Claims 7-9.

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