Effect of surface treatments on electrical properties of β-Ga2O3

Abstract

The effect of various combinations of gaseous (ultraviolet/O3), liquid (HCl, buffered oxide etch, and H2O2), or plasma (CF4 and O2) treatments of the surface of β-Ga2O3 was quantified by current–voltage and capacitance–voltage measurements of rectifier structures. Plasma exposure (13.56 MHz, 24 kW/cm2) always led to significant degradation of the surface, as evidenced by large increases in rectifier reverse current and ideality factor (from 1.01 in control samples to ∼3.8 in plasma exposed samples, indicating additional defect-related carrier transport mechanisms) and lowering of the Schottky barrier height (from 1.21 eV in control samples to 0.75–0.86 eV in plasma exposed samples) and diode rectification ratio, with degraded reverse recovery characteristics. This was true of both CF4 and O2, even though it is known that fluorine incorporation in the near-surface leads to donor compensation and an increase in barrier height. Damage from the plasma exposure was not fully recovered by annealing at 500 °C. The O3 and liquid chemical cleans did lead to reduced reverse current in rectifiers, with no measurable decrease in barrier height, increase in ideality factor, or degradation of reverse recovery characteristics. Surfaces treated in this manner did not significantly change for anneals up to 500 °C; however, the Ni/Au contacts already show degradation after annealing at 350 °C.