Calculation Optimization And Experimental Study On Hydride Vapor Phase Epitaxial Growth Of Thick Gallium Nitride Films

GaN is a wide band gap semiconductor with a very wide range of applications.GaN based devices are mainly produced by the hetero-epitaxial method due tolarge-size GaN single crystal materials are difficult to prepare. In recent years, hydridevapor phase epitaxy method become a research hot spot due to its larger growth rate andits supply of uniform and large-size thick GaN film. Numerical calculation have a greatadvantage in improving the growth system and optimize the growth process Itsco-ordination with the crystal growth experiment is expected to seek the optimizationprocess for the growth of high quality GaN crystalIn this thesis, firstly, the influence law include the distance between the gasinlet,GaCl carrier gas flow rate and main carrier gas N2flow rate to crystal growth havebeen investigated by using the HEpiGaNS code based on the finite element method. It isachieved mainly through studying one and two-dimensional concentration distributionimages near the substrate on the reaction gas GaCl and NH3,GaN growth rate atdifferent conditions, the flow field in the reaction chamber and Ⅴ/Ⅲ ratio near thesubstrate. Secondly, the stress and dislocations change in GaN growth process havebeen studied through studying various stress changes in different growth stages anddislocation values changes at different substrate height. Growth process parameterswhich is conducive to high-quality thick GaN film can be obtained by numericalcalculation. Lastly, HVPE-GaN growth experiments are conducted using theseparameters and its analysis of the structure and quality of the epitaxial film are carriedout through a series of characterization means such as XRD, SEM, EDS, RS and PL.The results are as follows: the distance between the gas inlet and the substrate havegreat influence on GaN crystal growth in vertical HVPE system, too long distance causetoo small growth rate and too short distance cause growth rate becomes large butextremely not uniform. It indicts that there is an optimal distance between the gas inletand the substrate at which the deposition features of GaN is best and analysis revealsthat this optimal distance is about80mm; The concentration distribution of GaCl gasand NH3gas near the substrate can be affected by GaCl carrier gas flow, theconcentration of the reaction gas is reduced with the decreases of GaCl carrier gas flowrate and the uniformity of the distribution is getting better, but the carrier gas flow isreduced to a certain level causes the deposition uniformity deteriorated.The experimentsreveal that GaN grow well under the GaCl carrier gas flow1200¹400sccm; Thereaction gas concentration distribution near the substrate are affected by N2gas flow,the main carrier gas in the reaction, and the instability of which may give rise to eddycurrent phenomenon in the reaction chamber, the experiments reveals that the optimalN2gas flow rate to the benefit of GaN crystal growth is about2800sccm; In HVPE growth system, the maximum of several kinds of thermal stress can be found in thecrystal growth edge, the dislocation density in crystal internal increases gradually withthe substrate height increasing.HVPE-GaN single crystal with high quality can be prepared by taking advantage ofoptimization of process parameters obtained by numerical calculation. We found theepitaxial film is GaN （002） monocrystalline with a hexagonal crystal structure and itsthickness is about4μm; We also prove the crystal with quite smooth has a high surfacequality; Small surface compressive stress was found in the crystal; We prove theFWHM of the rocking curve of （002） plane is160arcsec and the total dislocationdensity of the crystals is about7.7710⁸cm^-2; The defect emission peak with lowstrength was also found in the crystal.