Thermal desorption of ultraviolet–ozone oxidized Ge(001) for substrate cleaning

Abstract

X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), electron energy loss spectroscopy (EELS), and reflection high-energy electron diffraction (RHEED) have been used to show that 30 min exposures of a degreased and deionized-water-rinsed Ge(001) wafer to ultraviolet (UV)–ozone in laboratory air is sufficient to remove C contamination and form a nonpermeable passive amorphous GeO2 layer with a thickness of ≂1.8 nm. Subsequent annealing in ultrahigh vacuum (UHV) at ≥390 °C for ≥30 min resulted in desorption of the oxide layer and the exposure of a clean well-ordered Ge(001)2×1 surface. No impurities, including C and O, were detected by either XPS or AES. EELS spectra from the clean surface showed well-defined peaks corresponding to transitions involving dangling bonds, surface states, and surface plasmons. Shorter UV–ozone exposures (i.e., <30 min) often resulted in residual C contamination while incomplete oxide removal was obtained at lower oxide desorption temperatures. Ge overlayers deposited by molecular beam epitaxy at temperatures between 200 and 450 °C on UV–ozone processed substrates were found by a combination of plan-view and cross-sectional transmission electron microscopy to be highly perfect single crystals with abrupt film/substrate interfaces and no detectable dislocations or extended defects.