Numerical Simulation And Optimization Of Parasitic Deposition In Large-scale HVPE Reactor

GaN is the most important wide-bandgap semiconductor material and Hydride Vapor Phase Epitaxy?HVPE?is the principal method to grow GaN homogeneous substrate.During the growth of GaN homogeneous substrate by HVPE,severe parasitic depositions occur on the reactor walls,which will decrease the growth rate and the quality of films.In this study,numerical modelings are conducted for the parasitic depositions of GaN growth in a large-sized vertical HVPE reactor.Through comparison of modeling results with experimental data,the distribution of the parasitic deposition on reactor walls and the GaN growth rate are investigated,especially,the relationship between the flow rate of N₂ carrier gas and the parasitic deposition are determined.In order to further reduce the parasitic deposition,the difference between the original model and the new one are conducted by changing the geometric model of the reaction chamber.On this basis,the effects of different operating parameters on the parasitic deposition and growth rate are discussed.The main conclusions are as follows:1.At the base condition,the top wall parasitic deposition rate decreases gradually from center to edge,in agreement with the experimental result.For the side wall deposition there are eight high parasitic deposition zones,corresponding to GaCl nozzle tubes,indicating that the deposition mainly depends on the GaCl mass transport.The predicted growth rate at graphite susceptor is lower than the experimental one,but the trend is consistent.2.Keeping other conditions unchanged,increasing the flow rate of the NH₃ carrier gas N₂,the parasitic deposition rates and distribution areas of both top and side walls increase,while the growth rate on graphite susceptor decreases and uniformity increases;increasing the flow rate of the GaCl carrier gas N₂,the parasitic deposition rate and the distribution area are reduced both on top and side walls,while the growth rate on graphite susceptor increases and uniformity decreases.After increasing the rotation rate of the tray,there is little effect on the distribution of parasitic deposition on the top wall,which has a great influence on the side wall and can significantly increase the growth rate.3.Accounting for the current reaction chamber structure,parasitic deposition is still serious through the adjustment of parameters.To further reduce the parasitic deposition,change the geometry model of the reactor with the original top wall into an isolated N₂ inlet and simulate again.In order to further reduce the parasitic deposition,the geometry model of the reactor is changed,with the original top wall adding additional isolation N₂ inlet,and the simulation is carried out again.The modeling results show that:?1?After the improvement of the geometricmodel of the reaction chamber,the additional introduction of N₂ as the shielding gas between GaCl and NH₃ can effectively reduce the parasitic deposition;?2?Increasing the flow rate of isolation N₂,the parasitic deposition rates and distribution areas of side walls decrease.Accordingly,the growth rate on graphite susceptor decreases,while uniformity increases.?3?Increasing the flow rate of the GaCl carrier gas N₂,the parasitic deposition rate and the distribution area are reduced on side walls,while the growth rate on graphite susceptor increases and uniformity increases too.?4?Increasing the flow rate of the NH₃ carrier gas N₂,the parasitic deposition rate and the distribution area increase on side walls,while the growth rate on graphite susceptor are reduced and uniformity increases.?5?This article attempts to change the direction of gravity vector,the parasitic deposition rate and distribution area on side walls increase,while the growth rate decreases and the uniformity increases.?6?It is combined with the actual situation,when the inlet temperature is lower than the theeoretical temperature,the parasitic deposition rate decreases on side walls,and the growth rate decreases with the uniformity unchanged.