GaN MOS Capacitors and FETs on Plasma-Etched GaN Surfaces

Abstract

The electrical characteristics of gallium nitride (GaN) metal-oxide-semiconductor (MOS) capacitors and field-effect transistors (FETs) made on as-grown surfaces, dry-etched surfaces using reactive-ion etching (RIE), and wet-etch treated surfaces after the dry etch were measured. Capacitance and conductance techniques were used to obtain the MOS properties for capacitors. Devices with only an RIE plasma dry-etch process have poor yield and noisy capacitance in the low-frequency accumulation region. Those on dry/wet-etch treated samples have more negative ultraviolet (UV) assistant capacitance-voltage (CV) shift, and higher interface-state densities than those on as-grown samples, but have similar surface potential fluctuation. Threshold voltages of 2 V for an as-grown GaN MOSFET and 1 V for a dry/wet-etched MOSFET were measured. Maximum field-effect mobility for long-channel (L _ch = 100 μm) MOSFETs on the as-grown GaN wafer and the dry/wet-etched GaN wafer were obtained as 167 cm² V⁻¹ s⁻¹ and 119 cm² V⁻¹ s⁻¹, respectively. The higher interface trap density and lower field-effect mobility indicate that post-plasma-etch wet etching can only partially remove the damages from RIE.