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US-20260125825-A1 - GALLIUM NITRIDE SINGLE CRYSTAL SUBSTRATE AND METHOD OF PRODUCING SAME

US20260125825A1US 20260125825 A1US20260125825 A1US 20260125825A1US-20260125825-A1

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 resistivity of the substrate at 200° C. is 1×10 −2 Ω·cm or lower, and thermal conductivity of the substrate along a thickness direction at 200° C. is 80 W/mk or higher.

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 (6)

  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 resistivity of the substrate at 200° C. is 1×10 −2 Ω·cm or lower, and thermal conductivity of the substrate along a thickness direction at 200° C. is 80 W/mk or higher.
  2. 2 . The gallium nitride single crystal substrate according to claim 1 , wherein thermal conductivity of the substrate along a thickness direction at 25° C. is 120 W/mk or higher and 230 W/mk or lower.
  3. 3 . The gallium nitride single crystal substrate according to claim 2 , wherein provided that the thermal conductivity of the substrate along a thickness direction at 200° C. is R(H), and the thermal conductivity of the substrate along a thickness direction at 25° C. is R(L), R(H) and R(L) satisfy (R(L)−R(H))/R(L)<0.5.
  4. 4 . The gallium nitride single crystal substrate according to claim 1 , wherein the substrate includes an impurity containing germanium, and a germanium concentration is 1.0×10 18 cm −3 or higher.
  5. 5 . The gallium nitride single crystal substrate according to claim 4 , wherein the impurity contains oxygen, and an oxygen concentration is 1/10 or lower of the germanium concentration.
  6. 6 . 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. In a GaN single crystal substrate, an impurity is doped so that resistivity is reduced. In particular, for applications in high-power laser diodes and power devices, further reduction of resistivity of a GaN single crystal substrate is needed. From the viewpoint of reducing resistivity, it is necessary to increase the concentration of impurities. As one such impurity, germanium (Ge) has been studied because even at high concentrations it hardly degrades crystallinity of GaN (see, for example, Patent Document 1). RELATED APPLICATION Patent Document 1: Japanese Patent Application Publication No. 2021-195280 SUMMARY OF THE INVENTION A GaN single crystal substrate may in some cases be mounted on a heat sink when fabricated into a semiconductor device. From the viewpoint of enhancing heat transfer to the heat sink, a GaN single crystal substrate used for semiconductor devices is expected to have high thermal conductivity. However, thermal conductivity of a GaN single crystal substrate tends to decrease by addition of germanium. On the other hand, in an environment in which a semiconductor device is actually used, temperature may rise due to operation of the device. In this regard, thermal conductivity has conventionally been measured under room-temperature conditions, and no attention has been paid to measurement under high-temperature conditions. The present inventors examined variation of thermal conductivity of gallium nitride due to temperature, and it was confirmed that even when thermal conductivity is high under room-temperature conditions, it decreases due to rising temperature. Thus, with a GaN single crystal substrate, when germanium is added in a high concentration in order to reduce resistivity, even if high thermal conductivity can be achieved under room-temperature conditions, it may not be possible to maintain high thermal conductivity under high-temperature conditions. It is an objective of the present disclosure to provide a technique capable of maintaining high thermal conductivity under a high-temperature environment while reducing resistivity 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 resistivity of the substrate at 200° C. is 1×10−2 Ω·cm or lower,and thermal conductivity of the substrate along a thickness direction at 200° C. is 80 W/mk or higher. 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, it is possible to maintain high thermal conductivity even under a high-temperature environment while reducing resistivity in a gallium nitride single crystal substrate. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A illustrates a schematic cross-sectional view illustrating a part of a method of producing a gallium nitride single crystal substrate according to an embodiment of the present disclosure; FIG. 1B illustrates a schematic cross-sectional view illustrating a part of the method of producing a gallium nitride single crystal substrate according to an embodiment of the present disclosure; FIG. 1C illustrates a schematic cross-sectional view illustrating a part of the method of producing a gallium nitride single crystal substrate according to an embodiment of the present disclosure; FIG. 2 illustrates a flowchart illustrating the method of producing a gallium nitride single crystal substrate according to an embodiment; FIG. 3 is a schematic configuration diagram illustrating an ex