A reaction-transport model for AlGaN MOVPE growth

We present a systematic study of the complex chemistry and transport phenomena underlying metalorganic vapor phase epitaxy (MOVPE) of AlGaN; in particular, the mechanism underlying growth rate reduction at high temperatures and pressures. Thermodynamics and kinetics of formation of Lewis acid-base adducts of the organometallic precursors [TMGa-NH3 and TMAl-NH3] and the subsequent elimination of methane are investigated using hybrid density functional theory and transition state theory. The adduct pathway leads to the formation of stable dimer and trimer ring species containing Ga, Al, and N which strongly influence growth behavior in the reactor. Results from these studies, combined with reported data for gas-phase decomposition of TMGa and TMA1, are used in macroscopic, finite element reactor modeling studies to develop a reaction-transport model for AlGaN MOVPE growth. The model predicts growth rates in excellent agreement with experimental data for growth of AlGaN in different reactor configurations, including horizontal and 'close-spaced-injector' reactors. Formation of dimers and trimers is identified as the major pathway for decreased growth efficiency with increasing pressure. A pathway involving nucleation and growth of oligomers from dimers and trimers, and ultimately particle formation, is consistent with decreased growth efficiency for increasing temperature. (C) 1998 Elsevier Science B.V. All rights reserved.