Quasi-two-dimensional -Ga2O3 field effect transistors with large drain current density and low contact resistance via controlled formation of interfacial oxygen vacancies

Quasi-two-dimensional (2D) -Ga2O3 is a rediscovered metal-oxide semiconductor with an ultra-wide bandgap of 4.6-4.9 eV. It has been reported to be a promising material for next-generation power and radio frequency electronics. Field effect transistors (FETs) that can switch at high voltage are key components in power and radio frequency devices, and reliable Ohmic contacts are essential for high FET performance. However, obtaining low contact resistance on -Ga2O3 FETs is difficult since reactions between -Ga2O3 and metal contacts are not fully understood. Herein, we experimentally demonstrate the importance of reactions at the metal/-Ga2O3 interface and the corresponding effects of these reactions on FET performance. When Ti is employed as the metal contact, annealing of -Ga2O3 FETs in argon can effectively transform Schottky contacts into Ohmic contacts and permit a large drain current density of similar to 3.1 mA/m. The contact resistance (R-contact) between the Ti electrodes and -Ga2O3 decreased from similar to 430 to similar to 0.387 mm after annealing. X-ray photoelectron spectroscopy (XPS) confirmed the formation of oxygen vacancies at the Ti/-Ga2O3 interface after annealing, which is believed to cause the improved FET performance. The results of this study pave the way for greater application of -Ga2O3 in electronics.