25MBE Growth and Device Applications of Ga2O3
Masataka Higashiwaki
National Institute of Information and Communications Technology, Tokyo, 184‐8795, Japan
25.1 Introduction
Research and development on novel semiconductor materials is often motivated by requirements for new devices that may lead to not only the realization of new systems, but also improvements in the existing system performance. Owing to constant demands for power conversion to be ever more efficient, gallium oxide (Ga2O3) has attracted great attention as an emerging semiconductor due to its unique material properties, derived from an extremely large bandgap. However, Ga2O3 is by no means a new material from a historical point of view. With techniques to synthesize bulk single crystals, the crystal structures and material properties of Ga2O3 had already been studied in the 1950s–1960s [1,2]. Some melt growth and epitaxial thin‐film growth technologies for Ga2O3 were developed before the 1990s. In spite of this vast body of groundwork, Ga2O3 has remained largely unknown for a long while, in contrast to other wide‐bandgap materials such as SiC, GaN, and diamond.
25.2 Physical Properties of Ga2O3
25.2.1 Polymorphs
As is commonly the case with oxide semiconductors, Ga2O3 exhibits polymorphism with five types of polymorphs, labeled α, β, γ, δ, and ɛ [1]. The majority of research efforts have been devoted to the most stable monoclinic β‐Ga2O3, since its bulk single crystals can be synthesized by melt growth methods, as will ...