Effect of GaN surface treatment on Al2O3/n-GaN MOS capacitors

The surface preparation for depositing Al2O3 for fabricating Au/Ni/Al2O3/n-GaN (0001) metal oxide semiconductor (MOS) capacitors was optimized as a step toward realization of high performance GaN MOSFETs. The GaN surface treatments studied included cleaning with piranha (H2O2:H2SO4 = 1:5), (NH4)(2)S, and 30% HF etches. By several metrics, the MOS capacitor with the piranha-etched GaN had the best characteristics. It had the lowest capacitance-voltage hysteresis, the smoothest Al2O3 surface as determined by atomic force microscopy (0.2nm surface roughness), the lowest carbon concentration (similar to 0.78%) at the Al2O3/n-GaN interface (from x-ray photoelectron spectroscopy), and the lowest oxide-trap charge (Q(T) = 1.6 x 10(11) cm(-2) eV(-1)). Its interface trap density (D-it = 3.7 x 10(12) cm(-2) eV(-1)), as measured with photon-assisted capacitance- voltage method, was the lowest from conduction band-edge to midgap. (C) 2015 American Vacuum Society.