Arsenic oxide microcrystals in anodically processed GaAs - Electrochemicalgrowth, spectroscopy, and morphology

Anodic etching of GaAs wafers in concentrated HCl produces many As2O3 micro crystals (1-50 mu m 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: et ching times facilitate AS(2)O(3) microcrystal growth. Polarization-dependen t Raman spectroscopy identified the As2O3 microcrystals and accessed symmet ry changes of the GaAs surface induced by the electrochemical processing. R aman signals from quantum-size effect confined phonons in GaAs were not obs erved. Far-field photoluminescence of such samples shows a strong emission band centered around 540 nm. Spatially resolved spectroscopy and imaging (c athodoluminescence and near-field scanning optical microscopy) unambiguousl y indicate that the 540 nm emission comes from many weak emitters (AS(2)O(3 )) A few strong emitters originating from amorphous impurity inclusions are also identified in samples prepared in a macer cell. (C) 2000 The Electroc hemical Society. S0013-4651(99)10-018-1. All rights reserved.