CFD and reaction computational analysis of the growth of GaN by HVPE method

GaCl synthesis reaction during hydride vapor phase epitaxy (HVPE) growth of GaN in horizontal flow reactor has been analyzed using computerized fluid dynamics (CFD) and molecular estimates of the reaction rates. Finite element code FIDAP (commercially available from Fluent Inc.) [Fidap User Manual, Fluent Inc. [1]] has been used to obtain the flow pattern in the GaCl synthesis section of the HVPE reactor. As in the typical HVPE design, it was assumed that the flow pattern is weekly dependent on the temperature distribution in the reactor, i.e. the system in this part is virtually isothermal. The HCl+Ga(l) surface reaction rate has been estimated using ideal gas approximation for HCl impingement flux and predefined sticking coefficient for HCl adsorption on liquid Ga surface. In parallel, Ga evaporation process and transport has been accounted in the simulations.Using Ga evaporation rates, the total flux of transporting Ga has been obtained. The flux includes GaCl resulting from the surface reaction rate, and the Ga evaporation flux. The GaCl synthesis rate was obtained in function of the pressure, flow velocity and geometry of the reactor. The HCl to GaCl conversion degree in function of the above parameters was obtained for the several selected values of the sticking coefficient of HCl on liquid Ga surface. It was shown that for the typical design of the reactor, for the sticking coefficient below 0.01, the conversion rates depend on the sticking coefficient. For higher values of the coefficient the GaCl synthesis reaction is diffusion controlled and independent on the surface reaction kinetics.The calculations were made for the temperatures range of 800–1000 °C for which the Ga/GaCl ratio was determined. It was shown that, even in case of relatively low values of sticking coefficient for HCl, such as 0.01, gallium transport is dominated by GaCl for temperatures up to 1300 K. These results suggest that for the temperatures up to 1500 K Ga vapor transport by direct evaporation is inefficient, i.e. the sublimation growth of GaN is inefficient in this temperature range.