Cleaning chemistry of GaAs(100) and InSb(100) substrates for molecular beam epitaxy

The widely accepted sample-cleaning procedure for MBE substrates, involving the thermal desorption of native oxide-passivation layers in UHV, is examined using high resolution x-ray photoelectron spectroscopy. Oxide composition, carbon contamination, and substrate surface stoichiometry are followed for a variety of temperatures, for GaAs, Inx Ga1−xAs, and InSb substrates. The oxide desorption mechanism observed involves thermal reduction of As+5 to As+3 resulting in the further oxidation of the GaAs substrate surface and the additional formation of Ga2O3 and As0. At higher temperatures, first the As2O3 desorbs followed by the loss of Ga2O3. Carbon-contamination levels were minimized (<0.5% of a monolayer) by the etch removal of the chemical passivating layer by a HC1/EtOH strip immediately prior to vacuum introduction of the sample. The etch is done in inert-atmosphere conditions and gives total removal of both arsenic and gallium oxides, yet leaves the substrate stoichiometry unmodified. This method was quite effective for the Inx Ga1−xAs (x=0–1) system; however, halide-passivation films gave better results on InSb.