Adsorption and Dissociation of Trimethylindium on an Indium Nitride Substrate. A Computational Study

Abstract

A computational study of the adsorption and dissociation of trimethylindium (TMI) on an indium nitride (InN) substrate was performed, as an essential component of InN epitaxy in high-pressure chemical vapor deposition. Gibbs free energies of reaction and reaction rate constants were calculated for the adsorption/ desorption of TMI and its derivatives onto four model substrates of InN, for temperatures between 300 and 1400 K, and pressures between 1 and 100 atm. Similar properties were calculated for the methyl dissociation of the adsorbed species. The four model substrates were designed to represent the nitrogen surface of InN with various degrees of coverage. The model-substrates were constructed as four-shell clusters, which were structurally optimized by energy minimization. The electronic energies for the gaseous species were estimated using density functional theory, whereas, for the adsorbate-cluster adducts, the hybrid approach ONIOM was used, based on semiempirical molecular-orbital calculations and density functional theory. Thermodynamic properties and reaction rate constants were estimated using Debye's approximation for solids, vibrational frequencies obtained from normal vibrational analyses, statistical thermodynamics, and transition-state theory. Validation of the clusters was based on the indium-nitrogen distances and on heat capacity. Systems of coupled differential equations were solved to compute the time progression of the species concentrations at various temperatures (from 500 to 1300 K) and pressures (from 1 to 25 atm).