Study On Chemical Reaction Mechanism Of Aln Grown By High Temperature Mocvd

AlN is a kind of III-V nitride material with the excellent properties,and is widely used in many fields like high power devices,UV and deep UV electronic devices.Metal Organic Chemical Vapor Deposition（MOCVD）is a key technology for preparing AlN materials,the gas phase reaction of which determines the growth rate and uniformity of the films,and the surface reaction determines the surface morphology and growth quality of the films.However,due to the serious parasitic pre-reaction in the gas phase reaction and the low mobility of Al adsorbed atoms on the growth surface,the epitaxy of high-quality AlN films on sapphire substrates by MOCVD technology still faces severe challenges.To increase the growth temperature can enhance the transverse mobility of Al atom surface so that the quality and surface morphology of AlN crystal can be improved.Therefore,we choose to use MOCVD technology to grow AlN at high temperature.With the improvement of computer computing ability,the complex chemical reaction mechanism can be simulated by computational chemistry,so that the specific growth mechanism of AlN can be studied in depth,and suitable growth parameters can be determined in the subsequent practical process so as to produce the high-quality and high-performance AlN films.The main contents of this paper are as follows:（1）This paper applies the quantum chemical calculation software Gaussian,makes the thermo dynamical calculation of the adduct pathway,pyrolysis pathway and parasitic pathway of aminoacid polymerization and decomposition of AlN grown by MOCVD,analyzes the effects of temperature on the above pathways and judges the probability of occurrence of each reaction pathway.The results showed that TMAl and NH3 will spontaneously generate the adduct TMA1:NH₃ when NH₃ is excessive and the temperature T was less than 268 ^oC and then produce amino compounds by the elimination reaction,it is impossible for DMAlNH₂ to recombine NH₃ molecules at high temperature.TMAl:NH₃will be decomposed again when T is more than 300 ^oC.When NH₃ is excessive,the generated adduct TMA1:NH₃ will continue to bind to a NH₃ molecule,forming hydrogen bond adduct is more likely than coordination bond adduct.The pyrolysis of TMAl and MMAL requires high temperature activation.When T is more than 1000 ^oC,the pyrolysis of MMAl from DMAl will proceed spontaneously.Among the parasitic reactions of AlN,（MMAlNH）₂ and（MMAlNH）₃ are the most probable end-gas precursors.（2）This paper adopts the density functional theory to calculate the molecular structure and energy,combines the transition state theory to estimate the reaction rate and activation energy of gas-phase reaction,and selects seven surface reactions as surface reaction models.The surface reaction mechanism here does not consider the adsorption and reaction of NH3 and trimer on the surface,and the surface products are only adsorbed on the surface of Al（s）and AlN（s）,thus a relatively complete chemical reaction kinetics model of AlN-MOCVD is determined at high temperature.（3）Based on the above analysis results of growth characteristics and reaction mechanism of AlN,grove growth rate model of AlN films grown by MOCVD method is proposed and established.This model takes into account the gas chemical reaction of the growth source in the boundary layer.Based on grove model,the growth rate models were validated at different temperatures and pressures.The comparison results showed that the growth rate models at different substrate temperatures（400-900 ^oC）were in good agreement with the experimental values at constant pressure of 85 torr,with an average error of 4.34%;when the temperature is 600 ^oC the simulated values of the growth rate models under different pressure（30-270 torr）are in accordance with the experimental values,with an average error of 8.66%.