Study On Gas-Phase Reaction And Reactor Optimization In GaN HVPE Growth

GaN is an important wide bandgap semiconductor material,which is widely used in semiconductor lighting and power electronic devices.HVPE has the characteristics of high growth rate and strong controllability,so it is an ideal method for preparing GaN homoepitaxial substrates.Due to the severe gas phase parasitic reactions in the GaN growth of HVPE,it is very crucial to understand the gas-phase reaction pathway for controlling and optimizing the film growth.In this thesis,the gas phase reaction path of GaN growth by HVPE has been systematically studied by the density functional theory of quantum chemistry.On the basis of optimizing the molecular configuration of the gas phase reaction,the frequency and energy of the molecule are calculated,to judge whether the chemical reaction can proceed spontaneously from thermodynamics.The vertical HVPE reactor was optimized by CFD simulation,and the effects of different nozzle structures and process parameters on GaN growth and transport were discussed.The main results are as follows:1.In the HVPE reactor,for the six reactions between GaCl and NH₃,all have?G>0,indicating that GaCl can not react with NH₃.For GaCl₃:NH₃,only the reaction of eliminating one HCl in the molecule can be spontaneously carried out at a temperature higher than 1240 K,and the intramolecular elimination and the intermolecular elimination reaction of the remaining GaCl₃:NH₃ cannot be spontaneously carried out.2.Using the thermodynamic phase equilibrium theory,calculate the vapor pressure of Ga in the HVPE reactor with temperature change,and find that the Ga vapor pressure increases with the increase of temperature.When T=1300 K,the vapor pressure of Ga is 1.15 Pa.Therefore,the influence of gaseous Ga can not be ignored in the gas phase reaction.3.Gaseous gas easily reacts with HCl to form H radical.H radical is easy react with NH₃ to produce NH₂ radical.GaCl can react with NH₂ to form GaClNH₂ and GaCl?NH₂?₂.Two GaClNH₂reacts to form?GaClNH₂?₂,and then?GaClNH₂?₂ can react with NH₂ in sequence to form?GaCl?₂?NH₂?₃ and?GaCl?₂?NH₂?₄.Ga can continuously react with NH₂ to form GaNH₂,Ga?NH₂?₂,and Ga?NH₂?₃.4.The reaction rate constants of gaseous Ga with HCl and NH₃ with H were calculated by using the transition state theory.Combined with computational fluid dynamics simulation,it was found that both reactions were very rapid.Therefore,as long as gaseous Ga enters the HVPE reaction chamber,NH₂ is rapidly generated,and NH₂ activity is high,resulting in parasitic reactions in the HVPE reactor.5.The optimization design of HVPE reactor was carried out by CFD simulation.Discuss the effects of different nozzle structures and operating parameters on the transport process within the reactor.The results show that the concentration of NH₃ and GaCl above the substrate can be increased by reducing the import area of group III and V.Adding a group of N₂ inlets at the GaCl inlet center can optimize the concentration uniformity of NH₃ and GaCl.As the N₂₁ inlet rate and NH₃ flow in the NH₃₁ inlet increase,the uniformity of GaCl and NH₃ concentration increases.