Mechanisms for the reduction of the Schottky barrier heights of high-quality nonalloyed Pt contacts on surface-treated p-GaN

X-ray photoelectron spectroscopy (XPS) was employed to investigate the chemical bonding and electronic properties of the interfaces between Pt and p-GaN layers that were two-step surface treated using a buffered-oxide etch solution, and hence, to understand the surface-treatment time dependence of the Schottky barrier height (SBH). Current–voltage (I–V) measurements show that the effective SBH decreases with increasing surface-treatment time. The XPS results show that as the treatment time increases, the Ga 2p and Pt 4f core levels for the 20-min-treated samples shift toward the lower-binding-energy side by 0.6 and 1.5 eV, respectively, compared to the 0.5-min-treated one. It is further shown that the intensity of the oxygen core-level peak decreases with increasing treatment time. Based on the I–V and XPS results, the observed reduction of the effective SBHs is attributed to the combined effects of the effective removal of the native oxide and the shift of the surface Fermi level toward the valence-band edge.