GaAs surface oxide desorption by annealing in ultra high vacuum
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We have studied the desorption mechanism of Ga- and As-oxides on GaAs (100) by subjecting the substrates to two thermal processes in ultra high vacuum (UHV) conditions. The first process was an outgassing at 350 °C, and the second process consisted of an annealing at 530 °C. The pressure variations in the UHV chambers recorded during both thermal treatments showed a behavior related to the removal of As- and Ga-oxides from the substrate surface. The thermally treated GaAs (100) substrates were analyzed by in situ reflection high-energy electron diffraction (RHEED), Auger electron spectroscopy (AES), and ex situ atomic force microscopy (AFM). AFM images clearly showed the presence of surface pits on the GaAs (100) samples exposed to the high-temperature oxide desorption process. The pits have a density of the order of 109/cm2, and some are as deep as 120 angstroms. We explain the pits formation mechanism in terms of chemical reactions of the surface oxides with the elements of the substrate.
