MOCVD OF GAAS IN A HORIZONTAL REACTOR - MODELING AND GROWTH

Metalorganic chemical vapor deposition (MOCVD) of GaAs in a horizontal reactor was performed and the process mathematically modeled in two dimensions. Growth was performed at pressures of 1.0 and 0.1 atm. The mass flow rates of the reactants, trimethylgallium (TMG) and arsine, were held constant in all runs with the hydrogen carrier gas comprising the remainder of the flow. An advanced computational fluid dynamics code enhanced for chemically reacting non-isothermal flows was used to model the deposition process. Parameters used in the model included: reactor geometry and operating pressure; thermal boundary conditions; ratio of reactants; chemical reactions; total inlet gas flow rate; and molecular weights, thermal conductivities, heat capacities, viscosities, and binary diffusion coefficients of the gas-phase species. Densities were calculated from the ideal gas law. Heats of reaction were obtained from the enthalpies of formation of the individual species. A single surface reaction Ga(CH3)3+AsH3 --> GaAs(s)+3CH4 was assumed. Film thickness profiles predicted by the model were compared with those of the GaAs thin films grown in the modeled reactor. The predictions and data are in good agreement over the entire length of the deposition region for the low pressure and high flow rate run. At the lower flow rate and at atmospheric pressure, the model predicted much more uniform deposition profiles than were obtained experimentally. These results and possible explanations for the discrepancies between the model and the data will be presented. Work is in progress to refine the model by including additional chemical reactions, Soret diffusion, and three-dimensional simulations.