Production and evolution of composition, morphology, and luminescence of microcrystalline arsenic oxides produced during the anodic processing of (100) GaAs

GaAs when exposed to a 7 V anodic bias in aqueous HCl, forms pitted structu res from which visible photoluminescence has been observed. Previous work i n our laboratory identified the source of the luminescence to be arsenic ox ide microcrystals, formed during the electrochemical oxidation, which evolv e in composition and morphology during the course of the anodic processing. The density and size of pits is dependent on the solution conditions as we ll as the applied potential program (stepped vs swept to 7 V. At early time s (t < 30 min) the pits are composed of a mixture of small (similar to 1 mu m) and larger (10's of mu m) faceted microcrystals identified by x-ray pho toelectron spectroscopy and energy-dispersive x-ray analysis to be a combin ation of As(III) and As(V) oxides. At longer times As(III) oxides predomina te, and the smaller microcrystals are no longer observed, suggesting that t he smaller microcrystals are As(V) oxide, and that they evolve chemically i nto As(III) oxide over the course of the oxidation. A suitable reaction pat hway which explains the observed predominance of As(III) species is suggest ed. The luminescence properties of these electrochemically produced structu res were investigated by near-field excitation. The luminescent properties evolve in parallel with the morphology and composition although the form of the spectrum is invariant in time and consistent with that obtained from b ulk As2O3 and As2O5. The similarity of emission obtained from the two types of microcrystals suggests an impurity-related origin. (C) 1999 American In stitute of Physics. [S0021-8979(99)04221-8].