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

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 (D_it) measurement by using the low temperature conductance method, the amount of D_it in the conduction band side is also almost the same, while D_it in the valence band side is lowest for the (111) surface. Minimum detectable D_it 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.