Mass and charge transport in photoetching of GaAs

In the past decade, localized photoetching of rho-type III-V semiconductors has received much attention. The technique is especially attactive for applications where deep structures with high aspect ratios are required, but has been demonstrated to be equally suitable to produce other patterns based on local differences in etch rate introduced by light projection. The optics of photoetching have been treated in detail, recently. However, so far the chemistry and transport phenomena of the process, which are expected to be at least equally important factors, have received hardly any attention at all. One of the most interesting aspects of photoetching is the extremely high etch rate which can be obtained, locally. For GaAs and InP, values of up to 20 μm/s have been reported. In this paper, the authors present a model which can both account for the observed etch rates, quantitatively, and explain the form of the structures etched with visible and near U.V. light. Most experiments were performed with GaAs in acidic hydrogen peroxide solutions, using 352, 442, 514 and 633 nm laser sources. The principles discussed in this work, however, also apply to other photoetchants and semiconductors