ARXPS AND LEISS CHARACTERIZATIONS FOR CHEMICALLY ETCHED AND ION-BOMBARDED GAAS(100) SURFACES

The effects of chemical etching and noble gas ion bombardment on GaAs(100) surfaces were investigated by angular resolved x-ray photoelectron spectroscopy (ARXPS) and low energy ion scattering spectroscopy (LEISS). The results show that at the As received GaAs surface, Ga oxide is the major component, resulting in a Ga concentration slightly higher than As. Chemical cleaning by hydrochloride acid (HCl(conc.) to H2O=1:1) followed by solvent washing efficiently removed the oxide layer, but ARXPS showed a strong As enrichment occurs at the cleaned GaAs surface. Ion bombardment was carried out using 3 keV Ar ions with a beam current of 1 mA for 50 min. XPS results show that at steady state the ion-bombarded GaAs surface is depleted in As (As/Ga approximately 0.8), but ARXPS indicates an As increase at the very surface. This is further confirmed by Ne+ LEISS analysis, which shows the top layer As concentration is increased by 40% after ion bombardment. The results indicate that bombardment-induced compositional changes are due to Gibbsian segregation.