Sulfur passivation of Ge (0 0 1) surfaces and its effects on Schottky barrier contact

Abstract

The structure of a passivating sulfide layer on Ge (0 0 1) substrates treated in an aqueous sulfide solution is investigated using Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and coaxial impact-collision ion scattering spectroscopy (CAICISS). It is found from XPS analysis that the contribution from twofold co-ordinated Ge atoms is dominant in the S-treated Ge surface. The incident and azimuth angle dependencies of the Ge signal intensity are compared between the S-passivated and clean Ge surfaces in CAICISS measurements. The azimuth angle dependence exhibits clear 4-fold symmetry in both the S-passivated and the clean surfaces. From the incident angle dependence along [1 0 0] direction, almost the same shadowing and focusing effects are observed in both the surfaces. These results suggest that Ge surface is passivated by S atoms occupying bridge positions between adjacent surface Ge atoms. In order to examine the effect of S-passivation of Ge surfaces on the interface electrical properties, we perform I–V measurements of Au/S-passivated Ge Schottky diodes. It is found that the S-passivation is effective for obtaining uniform diode characteristics.