Sites for arsine adsorption on GaAs(001)

Abstract

Arsine adsorption on c(2 × 8) and (1 × 6) GaAs(001) at 303–573 K has been studied by internal-reflection infrared spectroscopy. We have discovered that arsine adsorbs onto two sites: second-layer Ga atoms and Ga dimers. On the c(2 × 8), arsine dissociatively adsorbs on second-layer Ga atoms, forming arsenic monohydrides and transferring two H atoms each to nearby As dimers. On the (1 × 6), arsine dissociatively adsorbs on Ga dimers, and also transfers H atoms to As sites. The saturation coverage of arsine at 303 K on the (1 × 6) is twice that on the c(2 × 8). Also, more As-H infrared bands are observed, indicating that several AsH x s are formed. Dosing the surfaces with arsine at successively higher temperatures from 303 to 473 K leads to the loss of adsorbed AsH x species. At 573 K, no change in the c(2 × 8) occurs upon extended exposure to arsine. However, on the (1 × 6), the Ga dime are replaced by As dimers during arsine dosing, and at 573 K, 1800 L of AsH 3 is sufficient to convert the (1 × 6) into the c(2 × 8) reconstruction. We conclude that during vapor-phase epitaxy of GaAs with trimethylgallium and arsine, AsH 3 decomposes on second-layer Ga atoms and Ga dimers. However, on the latter sites the arsenic is more likely to incorporate into the crystal, instead of desorbing as As 2 or As 4 .