The Numerical Simulation Study On Growth Of GaN Substrate Materal By Vertical HVPE System

Based on the CFD theory, growth of GaN with self-developed vertical HVPEsystem was simulated by the finite element analysis software.The temperature field distribution simulated by two-dimensional numericalsimulation showed that heating the substrate alone was not enough to meet thetemperature requirement of Ga boat, and the two temperature zones were able to meettheir temperature requirements when the graphite ring and substrate were heatedsimultaneously after a graphite ring was added around the gallium boat. In addition,the flow field distribution had significant impact on the temperature field. Suitableheating power of graphite ring was needed to ensure an appropriate temperaturedistribution in the reactor. The influences of the distance between GaCl inlet andsubstrate on velocity field and molar concentration of reactants were also describedqualitatively by two-dimensional simulation. It was shown that the flow field abovethe substrate was relatively stable and the molar concentration of reactants distributeduniformly when the distance was between10mm-25mm.Three-dimensional numerical simulation showed that flow field was stable whenthe distance between GaCl inlet and substrate was less than 15mm, and increased withdistance, the uniformity of molar concentration of reactants above the substrate wasimproved with the increase of distance. However, when the distance was above 15mmthe vortexes appeared near the substrate, and their size was increasing with theincrease of the distance, while the molar concentration of reactants decreased.Therefore the best height should be between 13mm-15mm.By changing the flow rateof reactants, it was found that surface deposition rate of GaN depend linearly on the GaCl flow rate, while nonlinear on the flow of NH3. Moreover, the flow rate of carriergases had significant impacts on velocity field and molar concentration of reactants.When the flow rate of N2, the main carrier gas, was below 0.25m/s, the flow field wasmore stable and the surface deposition rate of GaN was higher. Besides, in differentpipes and at different positions of the same pipeline, surface deposition rate of GaNvaried with the change of H2/N2. It is indicated that surface deposition rate of GaNdecreased at the position where the mass fraction of H2 is higher, while at the positionof lower mass fraction of H2, surface deposition rate of GaN increased. In addition,the rotation speed of substrate had no significant impact neither on flow field normolar concentration of reactants.In order to improve the uniformity of surface deposition rate, the HVPE reactorhad been optimized. The results showed that molar concentration of GaCl and thesurface deposition rate of GaN were more uniform than that in the original system,which provided a basis for further work.