Interface trap characterization of Al2O3/GaN vertical-type MOS capacitors on GaN substrate with surface treatments

We report on the interface trap properties Al2O3/GaN vertical-type metal-oxide-semiconductor (MOS) capacitors homogeneously grown on GaN substrates with different surface treatments. The electrical and microstructure characteristics are analyzed with regard to the behaviors and natures of different trap states at and close to the MOS interface. It is shown that only acid cleaning could not effectively suppress the interface traps, while a following (NH4)2S passivation drastically reduce the interface state density to the detection limit of ∼1011 cm−2eV−1. At the same time, border traps and fixed charges located close to the MOS interface are also suppressed, leading to a neglecting electrical hysteresis and frequency dispersion in the capacitance-voltage measurement.