Arsenic oxide microcrystals in anodically processed GaAs electrochemical growth, spectroscopy, and morphology

Anodic etching of GaAs wafers in concentrated HCl produces many As₂O₃ microcrystals (1-50 μm in size) on the GaAs substrate. The etching process and the nature of the luminescence from these GaAs surfaces have been explored in detail. The etch pits are initiated at point defect sites, not extended defects. High HCl concentration, high current density, as well as long etching times facilitate As₂O₃ microcrystal growth. Polarization-dependent Raman spectroscopy identified the As₂O₃ microcrystals and accessed symmetry changes of the GaAs surface induced by the electrochemical processing. Raman signals from quantum-size effect confined phonons in GaAs were not observed. Far-field photoluminescence of such samples shows a strong emission band centered around 540 nm. Spatially resolved spectroscopy and imaging (cathodoluminescence and near-field scanning optical microscopy) unambiguously indicate that the 540 nm emission comes from many weak emitters (As₂O₃). A few strong emitters originating from amorphous impurity inclusions are also identified in samples prepared in a macor cell.