| The hydride vapor phase epitaxy of GaN in a vertical flow reactor was studied in this paper by finite element method, which based on the theory of numerical simulation. The grid was meshed by the unstructured and adaptable grid.The influence of the substrate height (the vertical distance between GaCl outlet and the substrate) on the distribution of GaCl and NH3 concentration was studied with two-dimension and three-dimension simulation. The molar concentration vector of GaCl and NH3 and XY Plot Figure analysis showed that the distributions of GaCl and NH3 concentration on the substrates were affected by the vertical distance between GaCl outlet and the substrate. It is suggested that the the distance of the transported gas to the surface of substrate changed with the substrate height, inducing the gas diffusion or whirlpool with the increase of distance. The distance between 10mm to 20mm is preferable for the distribution of GaCl and NH3 on the substrates and the uniformity of GaN epilayer.The influence of the inlet velocity of main carrier gas N2 was studied with two-dimension and three-dimension simulation. The inlet velocity has little influence on GaCl and NH3 concentration above the substrate by two-dimension calculation. But in the three-dimension calculation, it is found that the influence is higher because of the asymmetrical NH3 pipe. After adding one NH3 pipe in the symmetrical position and two N2 pipes, the uniformity of NH3 and GaCl is improved.Three-dimensional simulation of the rotating substrate can be achieved. The impact of speed of substrate rotation was studied with three-dimension simulation. GaCl concentration on the substrates has a weakly dependence on the speed of substrate rotation, NH3 concentration on the substrates has a stronger dependence on that. It has been suggested using a small rotation velocity during GaN growth.CFD simulation is cost-saving, and provides theoretical basis for the optimizing GaN growth process and also guide the actual experiment. |
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