The interfacial chemical characteristics and electrical properties of the metal-oxide-semiconductor (MOS) diode using molecular beam epitaxy (MBE)-Al2O3 as a dielectric template followed by atomic layer deposited (ALD) Al2O3 on hydrochloric acid (HCl) solution-cleaned GaN were studied and correlated. The results are Compared with those using ALD-Al2O3 as the dielectrics. With in situ X-ray photoelectron spectroscopy (XPS) analyses, a significant amount of residual Cl on the HCl-cleaned GaN surface was detected. The residual Cl was reduced by annealing at 300 and 670 degrees C, two temperatures for ALD and MBE-Al2O3 growth, respectively, with the amount being further reduced by the 670 degrees C annealing. The electrical characteristics were consistent with the XPS analyses; well-behaved capacitance-voltage (C-V) characteristics were obtained in the MBE-template sample, while appearance of a bump in the C-V curves was observed in the ALD-sample without the MBE template. (C) 2008 Elsevier B.V. All rights reserved.