LASER INTERACTION WITH BR-GAAS(110) - ETCHING AND ATOMIC DESORPTION

Scanning tunneling microscopy was used to investigate changes in the s urface morphology of GaAs(110) induced by 2.3 eV photons from a Nd:YAG (yttrium aluminum garnet) laser. For clean surfaces, irradiation caus ed minimal changes. For surfaces decorated by islands of Br, however, irradiation created monolayer pits whose shapes reflected the chemisor ption structures, The desorption yield followed a square law for low l aser intensities (F less than or equal to 13.5 mJ cm(-2)) due to photo chemical conversion of GaBr to volatile GaBr3. 70-80% of the etch pits were composed of pair vacancies due to removal of gallium as GaBr3 an d 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 fr om pit edges. Growth along [110] is favored, reflecting the contrast i n surface bonding strengths. Atomic desorption is initiated by electro nic excitations, probably involving multiple electronic excitations. T he yield varies as F(3-3.5). AS With photoetching, it increases with b ase temperature. Both photoetching and laser-induced desorption result in stoichiometric removal, and the top layer can be removed by extend ed irradiation. [S0163-1829(98)10139-X].