Theoretical study of the Cl desorption reaction induced by H 2 in the chloride atomic layer epitaxy

Abstract

The chloride ALE (atomic layer epitaxy) technique is now common to grow GaAs crystals, where the GaCl molecule is used to supply Ga atoms for the As dangling bond site. The present ab initio molecular orbital calculations predict that Cl atoms are desorbed as HCl by the single-site reaction which is induced by H 2. The reaction scheme is represented as > GaCl + H 2 → > GaH + HCl, which is driven by the concerted electron delocalizations among those four atoms. It is shown that the reaction is endothermic by the amount of 30 kcal/mol and occurs through the four-centred transition state of “late-barrier” type. The activation energy is estimated to be 37–44 kcal/mol, which agrees well with the experimental value of 40–50 kcal/mol.