Chemical vapor deposition of gallium nitride from the GaCl3+NH3 system.: Theoretical study of the structure and thermodynamics of potential intermediates formed in the gaseous phase

Quantum chemical calculations at the B3P86/6-311G(d,p) level have been performed on potential intermediate molecules in the chemical vapor deposition (CVD) of GaN from the GaCl3 + NH3 system. The investigated molecules included the monomer (ClxGaNHx, x = 1-3) and oligomer species (Cl2GaNH2)(n) with n = 1-3 and (ClGaNH)(n) with n = 1-4 as well as the respective chain dimers and trimers. The calculations revealed the importance of intramolecular Cl...H hydrogen bonding and dipole-dipole interactions in determining the conformational properties of the larger species. Except for the ClGaNH monomer, the Ga-N bonding has a single bond character with a strong ionic contribution. Our thermodynamic study of the composition of the gaseous phase supported the predominance of the Cl3GaNH3 complex under equilibrium conditions. Additionally, the calculated Gibbs free energies of various GaCl3 + NH3 reactions imply the favored formation of "saturated" chain and cyclic oligomers below 1000 K.