Insulator-GaN interface structures formed by plasma-assisted chemical vapor deposition

Abstract

Interface properties of Si3N4/GaN and SiO2/GaN structures produced by CVD processes were investigated by X-ray photoelectron spectroscopy (XPS) and capacitance–voltage (C–V) methods, paying attention to surface treatments prior to insulator deposition. Electron cyclotron resonance assisted plasma chemical vapor deposition (ECR-PCVD) and radio frequency-assisted PCVD (RF-PCVD) were used. For the interfaces having natural oxides of GaN, the surface Fermi level was strongly pinned due to the existence of high density of interface states. A surface treatment in NH4OH solution was found to be effective in reducing natural oxides and interface states. Further reduction of interface states was realized by the N2 plasma treatment of GaN surfaces just prior to the deposition of insulating films. A minimum value of interface state density of 5×1010cm−2eV−1 was obtained for the Si3N4/n-GaN structures formed by ECR-PCVD with a combination of NH4OH treatment and N2 plasma treatment.