Simulation Optimization Study Of Mist-CVD Growth Of α-Ga₂O₃

As a typical wide bandgap semiconductor,gallium oxide（Ga₂O₃）has a wide bandgap（4.9 eV-5.3eV）,ultra-high Baliga’s figure of merit,and a super-high critical breakdown field,which means that Ga₂O₃ has great advantages in the field of high-voltage,high-power,high-frequency,and low-power electronics,making it a preferred material for new power devices and a current research hotspot.α-Ga₂O₃,as one of its polymorphs,is a metastable phase with a relatively widest bandgap（5.3 eV）,higher Baliga’s figure of merit（6726）,critical breakdown field（10 MV/cm）,and high transparency to ultraviolet light.After solving the material preparation problem,α-Ga₂O₃ is expected to have even greater potential in the preparation of high-power,low-power,and good pressure-resistant devices,and in ultraviolet photodetectors.Due to its hexagonal crystal structure similar to sapphire and gallium nitride,and the small lattice mismatch withα-Al₂O₃ in the a-axis and c-axis directions,it is promising to grow high-qualityα-Ga₂O₃ films on sapphire substrates by epitaxy.Therefore,the preparation of high-qualityα-Ga₂O₃ materials has become a current research hotspot.The Mist Chemical Vapor Deposition（Mist-CVD）method has attracted significant attention as a low-cost,energy-efficient technique for the preparation of gallium oxide（Ga₂O₃）due to its simplicity and efficiency.Achieving high growth rates and uniform growth ofα-Ga₂O₃ thin films in practical growth experiments requires tedious optimization and fine-tuning of various parameters.Therefore,this study employs numerical simulation software to investigate the Mist-CVD epitaxial growth ofα-Ga₂O₃ thin films.Existing simulations have only been conducted in a steady-state manner,allowing observation of the flow field under stable conditions but providing no information about the temporal variation of the flow inside the chamber.However,in thin film growth experiments,the nucleation stage in the early stages of epitaxy significantly affects the crystal quality.To analyze the flow field and reaction during the early growth stage,this study combines transient and steady-state simulations.By controlling parameters such as growth temperature and substrate angle,the growth process is simulated,providing scientific guidance for experiments.This approach saves considerable time and cost,greatly enhancing experimental efficiency,and providing support for Mist-CVD growth ofα-Ga₂O₃ thin films.1.This paper establishes a 2D Mist-CVD system chamber model to simulate and simulate the epitaxial growth ofα-Ga₂O₃thin films.Acetylacetone gallium is used as the precursor and N₂ as the carrier gas.The latent heat,specific heat,and saturated vapor pressure of liquid acetylacetone gallium are estimated at different temperatures.At the same time,parameters such as specific heat capacity,viscosity,and thermal conductivity of gaseous acetylacetone gallium are estimated.In addition,an approximate value of the binary diffusion coefficient that affects the diffusion ability between the mixed gases in the chamber is calculated.2.At a growth temperature of 450℃,a detailed analysis was conducted on the deposition rate distribution ofα-Ga₂O₃ thin films on the substrate during Mist-CVD growth,considering the temporal variation of acetylacetone gallium gas.By varying the growth temperature and referring to existing literature reports,a growth temperature of 550℃was selected for the analysis of other relevant parameters.Subsequently,adjustments were made to the substrate angle and position,and from the simulation results,it was observed that larger substrate angles and closer substrate positions to the outlet led to higher relative non-uniformity of the thin film.Furthermore,variations in N₂ flow rate in the chamber model were studied,and it was found that in order to achieve stable flow and better relative uniformity on the substrate,an N₂ flow rate of approximately 0.1 m/s should be chosen.After a series of simulation studies,optimized simulation conditions were obtained:substrate temperature of 550℃,substrate angle of 26.5°,substrate position at a distance of 78 cm from the outlet,and N₂flow rate at approximately 0.1 m/s.3.A transient simulation was conducted to investigate the mist chemical vapor deposition（Mist-CVD）growth ofα-Ga₂O₃ thin films.The simulation results revealed that the number of droplets in the quartz tube decreased from the bottom to the top,while the average diameter of the droplets increased from the top to the bottom of the tube.This distribution led to a significantly higher number of droplets at the front end of the substrate than at the middle and rear ends.The droplets located at the front end of the substrate climbed towards the rear end under the effect of the Leidenfrost phenomenon and their diameter gradually decreased.When the growth temperature was increased to550℃,the acetylacetone gallium droplets in the chamber experienced a region of negative pressure.The average diameter of the droplets on the substrate surface decreased overall and completely vaporized before reaching the rear end of the substrate.When the substrate angle was increased,the peak of the number of droplets on the substrate surface shifted towards the rear and a peak also appeared at the rear end.The average diameter of the droplets was larger in the area with a higher number of droplets.