THEORETICAL-STUDY OF THE CL DESORPTION REACTION INDUCED BY H-2 IN THECHLORIDE ATOMIC LAYER EPITAXY

The chloride ALE (atomic layer epitaxy) technique is now common to gro w GaAs crystals, where the GaCl molecule is used to supply Ga atoms fo r the As dangling bond site. The present ab initio molecular orbital c alculations predict that Cl atoms are desorbed as HCI by the single-si te reaction which is induced by H-2. The reaction scheme is represente d as > GaCl + H-2 --> > GaH + HCI, which is driven by the concerted el ectron delocalizations among those four atoms. It is shown that the re action is endothermic by the amount of 30 kcal/mol and occurs through the four-centred transition state of ''late-barrier'' type. The activa tion energy is estimated to be 37-44 kcal/mol, which agrees well with the experimental value of 40-50 kcal/mol.