Development of procedures for obtaining clean, low-defect-density Ge(100) surfaces

Abstract

A repeatable, in situ process was developed for preparing clean, low-defect-density Ge(100) surfaces based on scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS) measurements. Surfaces prepared by ion sputtering followed by annealing, wet chemical etching followed by oxidation and thermal desorption of the oxide layer, growth of a Ge buffer layer, and in situ plasma cleaning were compared. The first two methods produced surfaces with no impurities detectable by AES, however, STM images of the surfaces revealed numerous protrusions, vacancies, and other defects. Auger electron spectra and STM images recorded before and after annealing C contaminated surfaces suggested that the protrusions were three-dimensional C clusters formed at elevated temperatures. The low surface to volume ratio of the clusters makes them difficult to detect by either XPS or AES. Although XPS indicated that oxygen plasma treatment effectively removes C from Ge surfaces, images of the plasma treated surfaces still showed the protrusions attributed to C. In contrast, surfaces prepared by Ge buffer layer growth followed by annealing exhibited no protrusions, low-defect densities on the terraces (less than 2% of a monolayer), and evenly spaced terraces that reflect the misorientation of the crystal. Thus, the surfaces prepared by Ge buffer layer growth were determined to be the most suitable for atomic level nucleation and growth studies.