SITES FOR ARSINE ADSORPTION ON GAAS(001)

Arsine adsorption on c(2 x 8) and (1 x 6) GaAs(001) at 303-573 K has b een studied by internal-reflection infrared spectroscopy. We have disc overed that arsine adsorbs onto two sites: second-layer Ga atoms and G a dimers. On the c(2 x 8), arsine dissociatively adsorbs on second-lay er Ga atoms, forming arsenic monohydrides and transferring two H atoms each to nearby As dimers. On the (1 x 6), arsine dissociatively adsor bs on Ga dimers, and also transfers H atoms to As sites. The saturatio n coverage of arsine at 303 K on the (1 x 6) is twice that on the c(2 x 8). Also, more As-H infrared bands are observed, indicating that sev eral AsHx species are formed. Dosing the surfaces with arsine at succe ssively higher temperatures from 303 to 473 K leads to the loss of ads orbed AsHx species. At 573 K, no change in the c(2 x 8) occurs upon ex tended exposure to arsine. However, on the (1 x 6), the Ga dimers are replaced by As dimers during arsine dosing, and at 573 K, 1800 L of As H3 is sufficient to convert the (1 x 6) into the c(2 x 8) reconstructi on. We conclude that during vapor-phase epitaxy of GaAs with trimethyl gallium and arsine, AsH3 decomposes on second-layer Ga atoms and Ga di mers. However, on the latter sites the arsenic is more likely to incor porate into the crystal, instead of desorbing as As-2 or As-4.