AN EFFICIENT METHOD FOR CLEANING GE(100) SURFACE

We report an efficient method for cleaning Ge substrates similar to the Ishizaka and Shiraki method for cleaning of Si. The Ge wafers are cleaned in running deionized water and etched with HF. A thin oxide layer was prepared by dipping in a mixture of H2O2 and H2O for a few seconds and the oxide layer was removed by dipping in HF. This procedure was repeated several times to ensure the removal of several atomic layers of Ge. Finally the thin oxide layer prepared as described above was thermally decomposed in ultrahigh vacuum by annealing in the temperature range 300-500-degrees-C. The resulting surface gave rise to sharp emission peaks due to surface states in UPS illustrating a clean surface. Impurities such as carbon and oxygen were below detection level in XPS and AES. Cross sectional TEM studies showed no defects associated with the cleaning procedure. Ge buffer layer growth and subsequent SiGe growth showed good morphology and no substrate/buffer defects.