First-Principles Modeling of the "Clean-Up" of Native Oxides during Atomic Layer Deposition onto III-V Substrates

The use of III-V materials as the channel in future transistor devices is dependent on removing the deleterious native oxides from their surface before deposition of a gate dielectric. Trimethylaluminium has been found to achieve in situ "clean-up" of the oxides of GaAs and InGaAs before atomic layer deposition (ALD) of alumina. Here we propose seven reaction mechanisms for "clean-up", featuring exchange of ligands between surface atoms, reduction of arsenic oxide by methyl groups, and desorption of various products. We use first-principles density functional theory (DFT) to determine which mechanistic path is thermodynamically favored. We also discuss the statistical likelihood of the interdependent pathways. "Clean-up" of an oxide film is shown to strongly depend on electropositivity of the precursor metal, affinity of the precursor ligand to the oxide, and the redox character of the oxide. The predominant pathway for a metalloid oxide such as arsenic oxide is reduction, producing volatile molecules or gettering oxygen from less reducible oxides. We therefore predict that "clean-up" of III-V native oxides mostly produces As-4 gas, but also GaAs solid or InAs solid. Most C is predicted to form C2H6 but with some C2H4, CH4, and H2O. An alternative pathway is nonredox ligand exchange, which is a pathway that allow nonreducible oxides to be cleaned up.