Surface orientation dependence of interface properties of GeO2/Ge metal-oxide-semiconductor structures fabricated by thermal oxidation

Abstract

We have fabricated GeO2/Ge interfaces on (100), (110), and (111) orientation substrates by direct thermal oxidation. The x-ray photoelectron spectroscopy analyses suggest that the Ge oxides are composed of GeO2 and have almost the same interfacial structure, independent of the surface orientations. The gate current conduction mechanism through the GeO2/Ge metal-oxide-semiconductor structure is dominated by Fowler–Nordheim tunneling. In addition, the barrier height between Ge and GeO2 is evaluated to be 1.2–1.4 eV. In interface trap density (Dit) measurement by using the low temperature conductance method, the amount of Dit in the conduction band side is also almost the same, while Dit in the valence band side is lowest for the (111) surface. Minimum detectable Dit is lower than 1×1011 eV−1 cm2 for all the orientations. These surface orientation dependences of the GeO2/Ge interface properties are quite different from those of the SiO2/Si interface.