Novel Method for High Speed SiC Vapor Growth
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0911-B05-09
Novel Method for High Speed SiC Vapor Growth Xiaolin Wang1, Cai Dang1, Hui Zhang1, and Michael Dudley2 1 Mechanical Engineering, Stony Brook University, Stony Brook, NY, 11794 2 Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794
ABSTRACT A comprehensive numerical model combining heat transfer, sublimation, species transport, and powder porosity evolution of SiC sublimation growth process is developed. The mechanism of vapor transport is described, in which a driving force is introduced to explain vapor transport. A new method to increase crystal growth rate is proposed based on the model. The new method includes changing the initial powder porosity and creating a hole in the packed powder. Simulation results for the case with a central hole and without hole are presented. The results show that the powder sublimation rate increases by creating a hole, and it is also validated by experiments. The results also reveal that the mass of the as-grown crystal increases if the powder sublimation rate increases. Finally, the powder geometry is optimized using numerical simulations. INTRODUCTION Silicon carbide is an important promising semiconductor material for electrical and optoelectronic applications in the area of high power, high temperature, high frequency and intense radiation[1, 2]. SiC crystals are typically produced by the sublimation method from SiC source at a temperature above 2000 oC under an argon environment. Sublimation growth process consists of the following steps: sublimation of source material, transport in the gas phase, impingement of atoms at the seed surface, surface diffusion and surface adsorption/desorption[3]. In the past decades, many research groups have worked on growing SiC bulk crystals and improving the crystal growth rate[4]. Traditional approaches are to increase furnace temperature or change pressure to enhance the growth rate. However, high cost of inert crucible at high temperature and impurity caused by crucible degradation set limit on the maximum growth rate. Furthermore, certain chemical species in the crucible material may alter the crystal growth habit by changing the fastest growth direction. Stresses and defects may be caused in the crystal via incorporation of impurities from crucible. Moreover, existing crucible and other components in the furnace are no longer passive at high temperatures as their vapor pressure may be significant, or they may react with the source material (SiC powder). The effect of pressure on growth rate is less significant compared with temperature. Heat and mass transport in the powder source plays an important role on sublimation rate. However, little has been known about the mechanism of species transport inside the powder until recently. Because the sublimation growth is operated at extreme high temperatures in a closed
enclosure, it is very difficult to perform the measurement and understand the growth process. To understand powder sublimation, porosity evolution during sublimation and its impacts on s
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