Laser interaction with Br-GaAs(110): Etching and atomic desorption

Abstract

Scanning tunneling microscopy was used to investigate changes in the surface morphology of GaAs(110) induced by 2.3 eV photons from a Nd:YAG (yttrium aluminum garnet) laser. For clean surfaces, irradiation caused minimal changes. For surfaces decorated by islands of Br, however, irradiation created monolayer pits whose shapes reflected the chemisorption structures. The desorption yield followed a square law for low laser intensities $(F<~13.5{\mathrm{mJ}\mathrm{}\mathrm{cm}}^{\mathrm{\ensuremath{-}}2})$ due to photochemical conversion of GaBr to volatile ${\mathrm{GaBr}}_{3}.$ 70--80% of the etch pits were composed of pair vacancies due to removal of gallium as ${\mathrm{GaBr}}_{3}$ and arsenic as molecular As. These photochemical processes are enhanced by photothermal effects, even in the low intensity regime. Pit growth after Br depletion occurs via laser-induced desorption of Ga and As from pit edges. Growth along [11\ifmmode\bar\else\textasciimacron\fi{}0] is favored, reflecting the contrast in surface bonding strengths. Atomic desorption is initiated by electronic excitations, probably involving multiple electronic excitations. The yield varies as ${F}^{(3--3.5)}.$ As with photoetching, it increases with base temperature. Both photoetching and laser-induced desorption result in stoichiometric removal, and the top layer can be removed by extended irradiation.