Mechanism Of Heat Transport Of SiC Growth By PVT

As the wide band-gap semiconductor,silicon carbide single crystal has been widely applied in the areas of high temperature,high power,high frequency and strong radiation baecuse of its outstanding physical properties.Thus far, the grown SiC crystals don't meet the evering-increasing demands on the crystal size and quality, therefore, the SiC-based devices make slow progress in their widespread application.How to grow large diameter and high quality SiC bulk single crystal is a urgent research task with definite application value.As for growth method of SiC bulk single crystals,physical vapor transport,aslo known as the modified Lely method, is one of the most widely used growth techniques.But there are many technical issues that have not been effectively solved.A main issue in SiC bulk single growth is that it is very difficult to accurately measure the temperature and control the thermal field inside the crucible under the growth condition.Therefore,it is very important and urgent to investigate the basic physics of heat transport during SiC growth process in order to further know the temperature distribution, to understand the mechanism of SiC crystal growth more exactly, to modify the growth system more effectively,and to optimize the process parameters more efficiently.The SiC growth process involves multi-phase,multi-component,and multi-mode of heat transport.Based on the thermadynimics and growth kinetics,this thesis firstly investigates the effects of temperature and temperature gradient on equilibrium partial pressures of vapor species and the ratio of the number of Si atoms to that of carbon.The influences of thermal condition on the graphitization of the powder source are also investigated,and an analytical mode is developed to describle the ralationship between the growth rate and temperature.Secondly,the heat transport mode involved in the different parts ot the growth system are investigated and an order-of-magnitude study is carried out with the motivacation of achieving a basic understanding of the complex thermal transport phenomena in the growth system.Thirdly,a thermal resistance analysis mode of the growth system is developed to estimate the temperatures of the key nodes.This mode has the advantages of simplicity and quick feedback.It can provide a better understanding of the thermal behavior of the furnace as well.Fourthly, a program of physics vopor transport SiC crystal growth heat transport finite element analysis system has been worked out.Compared with experimental measurements from three aspects,the numerically predicted results are satisfying.Finally,the distributions of magnetic vector potential,inducting current,and the Joule heat as well as the time evolution of the thermal field in the growth system are analysed.The effects of input power,operating frequency,coupling-clearance,space of turns of coil,thickness of the crucible wall,shape inside crucible,and different coil positions on the SiC growth are investigated.In addition,the impacts of the different length of grown crystal and the seed mouting method on the SiC growth are also considered.