The influence of stationary spatially homogeneous Townsend discharge on the (1 0 0) surface of semi-insulating GaAs samples is studied. Samples exposed to both electrons and ions in a nitrogen discharge at a current density j = 60 μA cm~(-2) are studied by means of x-ray photoelectron spectroscopy, ellipsometry and atomic force microscopy. It is shown that an exposure to low-energy ions (<1 eV) changes the crystal structure of the semiconductor for a depth of up to 10-20 nm, although the stoichiometric composition does not change. The exposure to low-energy electrons (<10 eV) forms an oxide layer, which is 5-10 nm thick. Atomic force microscopy demonstrates that the change in the surface potential of the samples may exceed 100 mV, for both discharge polarities, while the surface roughness does not increase.
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