Experimental Determination of Carrier Effective Mass and Cross-plane Thermal Conductivity in Mist-CVD-Grown Ge-Doped α-Ga2O3 Epitaxial Films

Gallium oxide with the corundum crystal structure (α-Ga2O3) has attracted considerable attention as an ultrawide-bandgap (Eg ∼ 5.3 eV) n-type oxide semiconductor. Theoretical calculations predicted a high electron mobility of approximately 220 cm2 V–1 s–1 with a carrier effective mass (m*) of 0.25 m0 and a relatively low thermal conductivity (κ) of ∼12 W m–1 K–1. However, experimental verification of these properties remains limited. In this study, we systematically investigate the m* and cross-plane κ of Ge-doped α-Ga2O3 epitaxial films grown by mist chemical vapor deposition. X-ray diffraction revealed no significant structural differences among the films. Assuming a parabolic conduction band minimum, m* was estimated from thermopower and carrier-concentration measurements. The obtained m* was approximately 0.4 m0. The cross-plane κ was approximately 19 W m–1 K–1 and showed little dependence on Ge concentration. These results provide a foundation for the development of high-performance α-Ga2O3-based power electronic devices.