A computational study of gas-phase and surface reactions in deposition and etching of GaAs and AlAs in the presence of HCl

Gas-phase and surface reaction mechanisms underlying MOCVD of AlAs and GaAs in the presence of HCl are studied using quantum chemistry. Density functional theory and conventional transition state theory are used to determine kinetic constants of gas-phase reactions following the dissociation of AI(CH3)(3) and Ga(CH3)(3) and the subsequent reactions with HCl. The developed kinetic schemes are then explored through sensitivity analysis. Adsorption energies of the most abundant gas phase molecules as well as activation energies of key reactions on GaAs and AlAs (1 0 0) surfaces are predicted quantum chemistry computations. The surface is modeled as semiconductor clusters of increasing size. Comparisons of predictions to available experimental data show that a cluster need to reproduce the beta2(2 x 4) surface reconstruction in order to successfully predict the surface reactivity. Surface and gas phase kinetic schemes are developed on the basis of the calculations as well as published data. These reaction schemes are linked with a two-dimensional computational fluid dynamic model to simulate experimental growth rates measured in different reactors. The simulations suggest that the AlAs gas phase and surface chemistry differ from that of GaAs. In particular, the mechanism for desorption of CH3 and Cl from an AlAs surface is different from that active for a GaAs surface. (C) 2004 Elsevier B.V. All rights reserved.