Sublimation growth source materials

The source material will release excess silicon in the beginning of the growth cycle and be more carbon-rich in the end due to preferential depletion of silicon. This is a known problem and it is a matter of detailed control and an understanding of the dynamic transport mechanisms in combination with thermodynamics. Nevertheless, the result is invariably that SiC boules grown by seeded sublimation growth are Si-rich in the beginning and C-rich near the end, which creates yield issues. Simulation of the process is necessary to improve the situation. 

One of the prime advantages of the HTCVD approach is the resulting crystal properties. Due to the high purity of the gases, the material comes out intrinsically semi-insulating. Also, since the source material is produced on demand, the stoichiometry can always be kept the same, unlike the case with seeded sublimation growth. This will improve the yield of the grown material. 

The rubrene source material was purchased from Aldrich (purity > 98%) and purified by threefold sublimation under dynamic vacuum conditions. The rubrene layers were evaporated in a standard HWE reactor on freshly cleaved 2Mi muscovite mica. Two different growth rates were used by employing different... 

Aluminium contamination is seldom observed for low temperature vacuum sublimation. Aluminium has a low capture coefficient at low temperatures and it does not form refractory carbides with a low vapour pressure. Therefore, traces of aluminium can be easily removed by annealing the furnace in vacuum even if contamination occurs. However, if the material source is insufficiently pure, it can result in noticeable aluminium contamination, especially at elevated growth temperatures. For the bulk crystal growth, aluminium contamination is always observed when abrasive silicon carbide is used as source material [20,22]. The abrasive material usually is highly contaminated [1,22]. 

Sublimation method with spontaneous nucleation (mass crystallization). Crystal growth is carried out in cylindrical graphite crucibles (Fig. 14). Powder silicon carbide is used as a source material. Crucibles are heated in cylindrical furnaces with resistive or inductive heating. Growth proceeds in an inert atmosphere (argon, helium) at a temperature of 2500-... 

Sublimation is one of the main methods of growing silicon carbide. This method is employed for growth of the material for abrasive applications as well as for the growth of single crystals and epitaxial layers for use in semiconductor electronics. The idea of the method is fairly simple, and is based on material transport from a hot source of material to a substrate which rests at a somewhat lower temperature. The transport is performed by the intrinsic vapour of the material at a high temperature, usually in the range 1600-2700 °C. 

A new approach to the directed crystallisation of silicon carbide has been proposed by Vodakov and Mokhov [6]. Their idea was to exclude the conditions which could permit any uncontrolled nucleation. They employ a nearly flat source positioned close to the substrate and perform the growth under near-equilibrium conditions. This has ensured a high quality of the grown material. The method was named the sublimation sandwich method and it appeared to be very effective. 

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