Substrate Off-Cut Effect on the Performance of Enhancement-Mode β-Ga ₂ O ₃ Metal-Oxide-Semiconductor Field-Effect Transistors

This study examines the effect of a 6 degrees off-cut toward the a-plane (A-6 degrees) and m-plane (M-6 degrees) of the c-plane sapphire (c-plane) substrates on the performance of enhancement-mode beta-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs). All epitaxial layers were grown simultaneously by metal-organic chemical vapor deposition, and the devices were fabricated using the same process, so that substrate orientation was the only experimental variable. Hall measurements at room temperature showed an improvement in mobility from 13.7 cm(2)/V<middle dot>s (c-plane) to 20.5 cm(2)/V<middle dot>s (A-6 degrees) and 18.9 cm(2)/V<middle dot>s (M-6 degrees). In addition, density functional theory simulations were performed to evaluate the lattice mismatch between beta-Ga2O3 and differently oriented sapphire substrates. The study confirms that off-cut substrates improve the crystalline quality and translate these improvements into fully fabricated, normally off transistors. In the fabricated MOSFETs, the on-resistance decreases from 1.85 k Omega mm (c-plane) to 0.45 k Omega mm (A-6 degrees) and 0.70 k Omega mm (M-6 degrees). Electrical benchmarking of c-plane, A-6 degrees, and M-6 degrees devices showed that devices grown on A-6 degrees substrate achieve the best overall performance among the three substrates, indicating that substrate engineering is an effective method for advancing beta-Ga2O3 power devices.