Epitaxial substrate and method for producing epitaxial substrate

Abstract

Disclosed is a crack-free epitaxial substrate with reduced warping, which uses a silicon substrate as a base substrate. Specifically disclosed is an epitaxial substrate which is obtained by forming a group of group III nitride layers on a (111) single crystal Si substrate such that the (0001) crystal plane is roughly parallel to the substrate surface. The epitaxial substrate is provided with: a buffer layer and a crystalline layer formed on top of the buffer layer. The buffer layer is obtained by forming contiguous laminated units comprising: a composition-modulated layer having an inherent compressive strain as a result of repeatedly and alternately laminating a first unit layer and a second unit layer, which have different compositions; a termination layer that is formed on the uppermost part of the composition-modulated layer, and that maintains the compressive strain inherent in the composition-modulated layer; and an enhanced-strain layer that is formed on the termination layer, and that increases the compressive strain inherent in the composition-modulated layer.

Description

technical field [0001] The present invention relates to epitaxial substrates for semiconductor elements, and more particularly to epitaxial substrates made of Group III nitrides. Background technique [0002] Nitride semiconductors are used as light-emitting devices such as LEDs or LDs, or high-frequency / large Power electronic devices are attracting attention with semiconductor materials. For example, a HEMT (High Electron Mobility Transistor) device in which a barrier layer made of AlGaN and a channel layer made of GaN are stacked is a device that utilizes the following characteristics: strong polarization effect (spontaneous electrode) Polarization effect and piezoelectric polarization effect) generate high-concentration two-dimensional electron gas (2DEG) at the stack interface (heterointerface) (for example, refer to Non-Patent Document 1). [0003] As a base substrate used for an epitaxial substrate for HEMT devices, a single crystal (heterogeneous single crystal) hav...

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Problems solved by technology

However, the crystalline quality of the resulting GaN film is by no means better than when SiC or sapphire is used as the base substrate

Therefore, in the case of producing electronic devices such as HEMTs using existing technologies, there are problems such as low electron mobility, leakage current when turned off, or lower withstand voltage.

[0013] In addition, in the method disclosed in Patent Document 4, since large convex bends are intentionally generated during device fabrication, cracks may occur during device fabrication depending on layer formation conditions.

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