Crystal growth seeded sublimation

There are similarities between seeded sublimation growth and HTCVD in that solid particles sublimate in the reactor and the vapor condenses on a seed crystal maintained at a lower temperature. However, the differences are quite dramatic and the outcome even more so. Take, for instance, the dynamics governing the growth... 

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. 

Since 1990 high quality SiC wafers of 35 mm diameter are commercially available from single crystal 6H-SiC boules, produced via a seeded-sublimation growth technique [134]. In this process, nucleation occurs on a SiC seed crystal located at the top or bottom of a cylindrical growth cavity. As in the Lely process [135], SiC sublimes from a polycrystalline source at temperatures >2200°C under vacuum to form Si, Si2C, and SiC2 vapors... 

On the other hand, bulk crystals of 4H-SiC and 6H-SiC are made by a physical vapor transport (seeded sublimation growth) technique known as the modified-Lely method [32]. High-quality bulk materials (threading dislocation... 

One of the methods of growing bulk GaN is a sublimation method [1-3], In this method, the source GaN powder and a seed crystal or a substrate facing the source are loaded in a crucible. Upon heating the crucible, the source powder sublimates and recrystallises onto the seed crystal or on the substrate. When a system needs a reaction gas such as NH3 for growth, the system is not a sublimation but a VPE system. Now, a 4-inch SiC wafer grown by a sublimation method is commercially available [4],... 

In 1978, Tairov and Tsvetkov [24] reported a sublimation technique to produce SiC boules for device application. They produced an 8 mm diameter by 8 mm long boule of SiC on a seed crystal placed within a graphite crucible. In a further study, growth of SiC boules up to 14 mm diameter and 18 mm in length were obtained [15]. 

Transport mechanisms in sublimation growth are complicated. Growth rate increases with increasing source temperature, increasing source to seed distance, decreasing pressure, and decreasing crystal-source distance [19,20,27-33]. 

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