3-DIMENSIONAL MODELING OF HORIZONTAL CHEMICAL VAPOR-DEPOSITION .1. MOCVD AT ATMOSPHERIC-PRESSURE

In order to clarify the conditions for which 2D and 3D theoretical models can realistically account for the actual growth rate distributions in horizontal CVD reactors, we have performed a systematic numerical study for the MOCVD of gallium arsenide from trimethylgallium and arsine in hydrogen or nitrogen as carrier gas at atmospheric pressure. Full 3D, 3D parabolic and 2D solutions were obtained for the system of equations governing the steady-state heat, momentum and mass transport. In particular, 3D effects were explored for reactors with large and small cross-sectional aspect ratios. The calculated growth rate distributions were compared with experimental data of Van de Ven et al. [J. Crystal Growth 76 (1986) 352]. Furthermore, the effects on growth rate uniformity of tilting the susceptor were investigated for various input flow rates. We have found that for light carrier gases, thermal (Soret) diffusion, which leads to more uniform growth rate distributions, must be included in the model. Furthermore, depending on the aspect ratio and thermal boundary conditions on the sidewalls, buoyancy-driven 3D flow effects can greatly influence the growth rate distribution throughout the reactor, under conditions judged stable against natural convection rolls when using only criteria based on vertical temperature gradients (i.e. at "subcritical Rayleigh numbers"). The modelling results emphasize the importance of the proper design of the lateral thermal boundary conditions for obtaining layers of uniform thickness. This study also shows that the much higher computational costs associated with a full 3D model, compared to 3D parabolic solutions, are justifiable only for small aspect ratio reactors operated at low flow rates. © 1990.