US-20260125824-A1 - GALLIUM NITRIDE SINGLE CRYSTAL SUBSTRATE AND METHOD OF PRODUCING SAME

Abstract

A gallium nitride single crystal substrate in which a low-index crystal plane closest to a principal surface of the substrate is a (0001) plane, wherein provided that thermal conductivity of the substrate along a thickness direction of the principal surface at 200° C. is R1(H), and thermal conductivity of the substrate along an in-plane direction at 200° C. is R2(H), R1(H) is 80 W/mK or higher and 120 W/mK or lower, and R2(H) is 80 W/mK or higher and 110 W/mK or lower.

Inventors

• Takayuki Suzuki
• Takashi Sato
• Toshio Kitamura
• Tetsuji Fujimoto

Assignees

• SUMITOMO CHEMICAL COMPANY, LIMITED

Dates

Publication Date

20260507

Application Date

20251022

Priority Date

20241101

Claims (4)

1. 1 . A gallium nitride single crystal substrate in which a low-index crystal plane closest to a principal surface of the substrate is a (0001) plane, wherein provided that thermal conductivity of the substrate along a thickness direction of the principal surface at 200° C. is R1(H), and thermal conductivity of the substrate along an in-plane direction at 200° C. is R2(H), R1(H) is 80 W/mK or higher and 120 W/mK or lower, and R2(H) is 80 W/mK or higher and 110 W/mK or lower.
2. 2 . The gallium nitride single crystal substrate according to claim 1 , wherein provided that thermal conductivity of the substrate along the thickness direction of the principal surface at 25° C. is R1(L), R ⁢ 1 ⁢ ( L ) ⁢ is ⁢ ⁢ 120 ⁢ W / mK ⁢ or ⁢ higher , and R ⁢ 1 ⁢ ( H ) ⁢ and ⁢ R ⁢ 1 ⁢ ( L ) ⁢ satisfy ⁢ ( R ⁢ 1 ⁢ ( L ) - R ⁢ 1 ⁢ ( H ) ) / R ⁢ 1 ⁢ ( L ) ≤ 0.5 .
3. 3 . The gallium nitride single crystal substrate according to claim 1 , wherein provided that thermal conductivity of the substrate along the in-plane direction at 25° C. is R2(L), R ⁢ 2 ⁢ ( L ) ⁢ is ⁢ ⁢ 150 ⁢ W / mK ⁢ or ⁢ higher , and R ⁢ 2 ⁢ ( H ) ⁢ and ⁢ R ⁢ 2 ⁢ ( L ) ⁢ satisfy ⁢ ( R ⁢ 2 ⁢ ( L ) - R ⁢ 2 ⁢ ( H ) ) / R ⁢ 2 ⁢ ( L ) ≤ 0.6 .
4. 4 . A method of producing a gallium nitride single crystal substrate, the method comprising: (a) preparing a base substrate constituted from a gallium nitride single crystal in which a low-index crystal plane closest to a principal surface of the base substrate is a (0001) plane; and (b) epitaxially growing a gallium nitride single crystal on the principal surface of the base substrate, wherein in (b), under an ammonia-containing atmosphere with a growth pressure greater than 1 atm and 1.5 atm or lower, a source gas for forming the gallium nitride single crystal is supplied onto the base substrate, and concurrently ammonia is supplied from around a support member supporting the base substrate.

Description

FIELD AND BACKGROUND OF THE INVENTION The present disclosure relates to a gallium nitride single crystal substrate and a method of producing same. Group III nitride semiconductors, typically represented by gallium nitride (GaN), are widely used as materials for semiconductor devices such as light-emitting devices and electronic devices. In order to improve the quality (e.g., semiconductor characteristics) of semiconductor devices constituted from group III nitride semiconductors, it has been desired to produce semiconductor stacks for manufacturing semiconductor devices or free-standing nitride semiconductor substrates so as to have satisfactory crystal quality. A semiconductor device may be mounted on a heat sink in order to diffuse heat generated therein. From the viewpoint of enhancing heat transfer to the heat sink, high thermal conductivity is required for a GaN single crystal substrate that is used for the semiconductor device (see, for example, Japanese Patent Application Publication No. 2008-179536). RELATED APPLICATION Patent Document 1: Japanese Patent Application Publication No. 2008-179536 SUMMARY OF THE INVENTION In an environment where a semiconductor device is actually used, the temperature may rise due to the operation of the device. On the other hand, the thermal conductivity of a GaN single crystal substrate has heretofore been measured under room temperature conditions, and measurement under high temperature conditions has not received much attention. Against this background, the present inventors have examined variations in the thermal conductivity of gallium nitride due to temperature, and confirmed that the thermal conductivity of gallium nitride tends to decrease as the temperature increases. For this reason, it is required that a GaN single crystal substrate used for a semiconductor device be capable of maintaining high thermal conductivity so as to exhibit desired heat dissipation even when the temperature of the semiconductor device rises. The present disclosure aims to provide a technique for maintaining high thermal conductivity under high-temperature environments in a gallium nitride single crystal substrate. According to one aspect of the present disclosure, there is provided a gallium nitride single crystal substrate in which a low-index crystal plane closest to a principal surface of the substrate is a (0001) plane, wherein, provided that thermal conductivity of the substrate along a thickness direction of the principal surface at 200° C. is R1(H), and thermal conductivity of the substrate along an in-plane direction at 200° C. is R2(H),R1(H) is 80 W/mK or higher and 120 W/mK or lower, and R2(H) is 80 W/mK or higher and 110 W/mK or lower. According to another aspect of the present disclosure, there is provided a method of producing a gallium nitride single crystal substrate, the method including: (a) preparing a base substrate constituted from a gallium nitride single crystal in which a low-index crystal plane closest to a principal surface of the base substrate is a (0001) plane; and(b) epitaxially growing a gallium nitride single crystal on the principal surface of the base substrate,wherein in (b), under an ammonia-containing atmosphere with a growth pressure greater than 1 atm and 1.5 atm or lower, a source gas for forming the gallium nitride single crystal is supplied onto the base substrate, and concurrently ammonia is supplied from around a support member supporting the base substrate. According to the present disclosure, high thermal conductivity can be maintained in a gallium nitride single crystal substrate even under high-temperature environments. BRIEF DESCRIPTION OF DRAWINGS FIG. 1A is a schematic cross-sectional view illustrating a part of a method of producing a gallium nitride single crystal substrate according to one embodiment of the present disclosure; FIG. 1B is a schematic cross-sectional view illustrating a part of a method of producing a gallium nitride single crystal substrate according to one embodiment of the present disclosure; FIG. 1C is a schematic cross-sectional view illustrating a part of a method of producing a gallium nitride single crystal substrate according to one embodiment of the present disclosure; FIG. 2 is a flowchart illustrating a method of producing a gallium nitride single crystal substrate according to the embodiment; FIG. 3 is a schematic configuration diagram illustrating an example of an HVPE apparatus; FIG. 4 is a diagram illustrating thermal conductivity R1 in a thickness direction at 25° C. and 200° C. in an example; and FIG. 5 is a diagram illustrating thermal conductivity R2 in an in-plane direction at 25° C. and 200° C. in an example. DETAILED DESCRIPTION Findings Obtained by the Inventors First, findings obtained by the present inventors will be described. The present inventors have examined a method by which gallium nitride can maintain high thermal conductivity even at high temperatures. In general, since a GaN crysta