Bulk crystal growth, methods

Overview of Unit Operations. To maximize the electron or hole (carrier) mobility and thus device speed, ICs are built in single-crystal substrates. Methods of bulk crystal growth are therefore needed. The most common of these methods are the Czochralski and float-zone techniques. The Czochralski technique is a crystal-pulling or melt-growth method, whereas the float-zone technique involves localized melting of a sintered bar of the material, followed by cooling and, thus, crystallization. 

The studies of growth by the sandwich method have provided a better understanding of the sublimation growth peculiarities and they have formed the basis of the new approach to the bulk crystal growth of silicon carbide. The first successful results in this direction were reported by Tairov and Tsvetkov [7,8]. Currently, similar studies are being performed by a number of research groups and rather impressive progress has been achieved thus far see Datareview 8.1. 

Alternatively, boron contamination can cause serious problems. Unintentional boron doping is observed both for epitaxial layer growth and for bulk crystal growth. Boron forms a highly stable carbide with a very low vapour pressure. Once introduced into the furnace, it is difficult to remove. Boron contamination can result from the graphite parts of the furnace, from the source material and from evaporation from the reverse side of the substrate as well as from occasional sources. The boron content can be decreased by long anneals at elevated temperatures, although this method is not always effective. 

Fig. 44. Progress in production of high-quality bulk single crystals connected with understanding crystal growth phenomena and subsequent technological improvements of crystal growth methods.

In addition to induction time measurements, several other methods have been proposed for determination of bulk crystallization kinetics since they are often considered appropriate for design purposes, either growth and nucleation separately or simultaneously, from both batch and continuous crystallization. Additionally, Mullin (2001) also describes methods for single crystal growth rate determination. 

Bulk growth of GaN and AIN has been achieved by a sublimation method and a sublimation sandwich method. Bulk GaN and AIN bulk crystals were proved to have high crystallinity. It will improve the quality of nitride-based optoelectronic devices, if these bulk crystals are used as substrates for homoepitaxial growth. The size of the bulk GaN, however, is not large enough at this moment, and enlargement of bulk GaN may be necessary. 

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