Numerical Simulation Of Growth Process Of Large AlN Crystals By Physical Vapor Phase Transfer Method

As the representative of the third generation of wide band gap semiconductor materials,aluminum nitride(AlN)crystals have the advantages of wide band gap,high breakdown electric field,high thermal conductivity,high electron saturation rate,and high radiation resistance.It has broad application prospects in the preparation of hightemperature,high-frequency,high-power electronic devices.The research and development of high-quality single-crystal aluminum nitride substrates and the manufacture of downstream related devices will greatly promote the development of communications,new energy,aerospace,national defense and other aspects.At present,the preparation technology of AlN substrates is still in the technical research and development stage worldwide,and the products are scarce and expensive.Many domestic research institutions and units have carried out related research,but in terms of crystal size,crystal quality and substrate device applications,there is a clear gap with the international advanced level.The physical vapor phase transfer(PVT)method is recognized as the mainstream technology that can produce high-quality,large-size AlN single crystals.However,due to limited testing methods,it is not possible to visually observe various conditions during crystal growth,and it is difficult to timely feedback for process adjustment.This paper uses the method of combining computer simulation technology and experiment to study the AlN crystal growth process.In this paper,the simulation software VR-PVT AlN is used to study the physical and chemical processes involved in the growth process,through the establishment of a crystal growth furnace simulation model and the setting of process parameters,including temperature field distribution,air flow transmission mode,heat conduction,heat radiation and crystal shape evolution,etc.Through the built-in calculation tools of the simulation software,the simultaneous solution of the enthalpy change equation,turbulence equation,thermodynamics and kinetics equations,and the iterative calculation of the convergence values of various parameters are performed to visually study the entire crystal growth process.On the basis of completing the establishment of the crystal furnace model,design simulation schemes for different factors that affect the crystal growth quality,and simulate the crystal growth process under different schemes.By adjusting the relative position of the heater and the crucible,the influence of different temperature gradients on the crystal growth and the growth rate are explored.And adjust the parameters that affect the temperature field distribution,such as the position of different temperature control points,power fitting and module thermal conductivity,to obtain a temperature field distribution structure that matches the experiment.Different schemes were designed for the factors affecting the crystal growth,such as the raw material state,inlet pressure,adhesive sheet material and cooling methods,to explore the effects on the crystal growth rate,thermal stress distribution,interface morphology changes,and dislocation distribution.Based on the simulation analysis results,the preparation of experimental materials was carried out,and the process scheme was applied to the actual long crystal process,and aluminum nitride single crystals with diameters greater than 52 mm were successfully prepared.Through the actual operation of the furnace body and the characterization results of the obtained crystal slices,it is proved that the orientation of the obtained crystal is(0002)direction,the internal thermal stress is low,the grain size is large and the crystallinity is high,and it has a high-quality structure.The experimental results verify the correctness of the fitting scheme,which shows that the simulation technology has important guiding significance for the research of aluminum nitride crystal growth process.