Direct determination of the barrier height of Au ohmic-contact on a hydrogen-terminated diamond (001) surface

Abstract

The barrier height ϕB of Au ohmic-contact on hydrogen-terminated p-type surface conductive layer (SCL) made on a boron-doped diamond (001) substrate has been directly determined by X-ray photoelectron spectroscopy (XPS). For this purpose, thin layer (thickness~3.6nm) of Au was deposited on the p-type SCL. The formation of nm-size Au-islands was identified by scanning electron microscopy. It became therefore evident that C 1s XPS spectra originate from diamond in the gap areas among Au-islands but not from diamond underneath the Au-islands. Two-dimensional energy band simulation was performed to show that the diamond band diagram in the gap areas among Au-islands become effectively identical to that of diamond underneath the Au-islands when SCL is eliminated only in the gap areas. In order to eliminate SCL in the gap area only, a VUV/ozone irradiation process was applied on the Au-island-covered sample. C 1s and Au 4f7/2 XPS spectra were measured for the sample before and after the VUV/ozone irradiation process. The peak binding energies and widths of C 1s and Au 4f7/2 XPS spectra are carefully considered to reach to the conclusion that ϕB=0.29±0.13eV. For the boron-doped present substrate, the current flow mechanism at the Au ohmic-contacts is expected to be thermionic emission and specific contact resistance RC is thus evaluated to be the order of 10−4Ωcm2.