Detailed studies on the defect-related surface states of plasma-exposed n-GaN surfaces were carried out. An anomalous flat portion appeared in the metal–insulator–semiconductor capacitance–voltage characteristics for the sample exposed to H2 plasma, corresponding to a localized peak at EC–0.5eV in the surface state density distribution. Atomic-force microscope and X-ray photoemission studies revealed the formation of Ga droplets on H2-plasma-treated GaN surfaces, caused by the desorption of N atoms in the form of NHx. These results suggested that a N-vacancy-related state near to the conduction-band edge was introduced on the H2-plasma-treated GaN surface. No such effects took place on the N2-plasma-treated GaN surfaces.

Discrete Surface State Related to Nitrogen-Vacancy Defect on Plasma-Treated GaN Surfaces. T.Hashizume, R.Nakasaki: Applied Physics Letters, 2002, 80[24], 4564-6