The nature of the interface between anodically grown oxide films and gallium arsenide substrates was studied using Raman backscattering. Room-temperature spectra of GaAs covered with as-grown anodic films as well as anodized samples dried under nitrogen at 250°C showed only the first-order longitudinal (LO) and transverse (TO) optical modes and the less-intense two-phonon features of the GaAs substrate. Heating the films at 450°C and above results in the appearance of intense LO (257 cm−1) and TO (198 cm−1) bands due to crystalline arsenic and the structureless Raman scattering near 200–250 cm−1 due to amorphous arsenic. Polarized Raman spectra indicate that elemental arsenic is not an intrinsic oxidation product of the room-temperature anodization. We suggest that the thermally induced solid-state interfacial reaction, As2O3+2GaAs→Ga2O3+4As, is responsible for the presence of arsenic at the oxide-semiconductor interface following annealing.
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Schwartz et al. (1979) studied this question.
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