Exploring heteroepitaxial growth and electrical properties of α-Ga2O3 films on differently oriented sapphire substrates

This study explores the epitaxial relationship and electrical properties of α-Ga2O3 thin films deposited on a-plane,m-plane,and r-plane sapphire substrates.We characterize the thin films by X-ray diffraction and Raman spectroscopy,and eluci-date thin film epitaxial relationships with the underlying sapphire substrates.The oxygen vacancy concentration of α-Ga2O3 thin films on m-plane and r-plane sapphire substrates are higher than α-Ga2O3 thin film on a-plane sapphire substrates.All three thin films have a high transmission of over 80％ in the visible and near-ultraviolet regions,and their optical bandgaps stay around 5.02–5.16 eV.Hall measurements show that the α-Ga2O3 thin film grown on r-plane sapphire has the highest con-ductivity of 2.71 S/cm,which is at least 90 times higher than the film on a-plane sapphire.A similar orientation-dependence is seen in their activation energy as revealed by temperature-dependent conductivity measurements,with 0.266,0.079,and 0.075 eV for the film on a-,m-,r-plane,respectively.The origin of the distinct transport behavior of films on differently oriented sub-strates is suggested to relate with the distinct evolution of oxygen vacancies at differently oriented substrates.This study pro-vides insights for the substrate selection when growing α-Ga2O3 films with tunable transport properties.