Structural Characterization of a Ga<sub>2</sub>O<sub>3 </sub>Epitaxial Layer Grown on a Sapphire Substrate Using Cross-Sectional and Plan-View TEM/STEM Analysis

Ga2O3 is a hopeful wide-band-gap semiconductor material for a next-generation power semiconductor. We performed crystal structure analysis on Ga2O3 film on sapphire substrate using cross-sectional transmission electron microscope (TEM) and atomic resolution plan-view scanning transmission electron microscopy (STEM). The TEM analysis suggested that the main Ga2O3 film is composed of κ-Ga2O3 or mixed crystal of κ-Ga2O3 and ε-Ga2O3. But, it is difficult to distinguish these two possibilities only by cross-sectional TEM. Contrast modulation of Ga atomic columns in the atomic resolution HAADF-STEM image showed that the main part of the Ga2O3 film was κ-Ga2O3 monolayer grown along the c-axis direction, and twins are formed.