Preparation of a clean Ge(001) surface using oxygen plasma cleaning

Abstract

The authors demonstrate a method to obtain a clean and smooth Ge (001) surface using oxygen plasma cleaning without sputtering or Ge regrowth. The preparation of the germanium surface consists of four cycles of ex situ wet etching using hydrochloric acid as the etchant and H2O2 as the oxidant. Subsequently, the sample is outgassed and exposed to an oxygen plasma for 30 min followed by thermal desorption of the newly formed oxide layer. Reflection high-energy electron diffraction shows a clear 2 × 1 reconstruction of the germanium surface. In situ x-ray photoelectron spectroscopy measurements confirm that the cleaned surface is free of carbon contamination and that no GeO2 remains. Angle-resolved photoemission spectra of the cleaned Ge show the peak associated with the Ge surface state indicating a very clean surface. Atomic force microscope images further indicate a smooth germanium surface with a mean surface roughness of approximately 3 Å after plasma cleaning.