Sublimation Growth of GaN and AIN

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 this Datareview, bulk growth of GaN and AIN by a sublimation method and of GaN by a sublimation sandwich method is described. The source powder was analysed. The bulk GaN obtained was characterised by XRD (X-ray diffraction), TEM (transmission electron microscopy), and so on. 

FIGURE 2 Bulk GaN obtained by the sublimation method, (a) Bulk GaN grown on sapphire substrate, (b) Free-standing bulk. 

FIGURE 4 XRD pattern of source powder (a) before and (b) after using for growth. 

FIGURE 5 Time dependence of each QMS peak. Ga-related compounds were exhausted. 

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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. 

Tanaka et al. (13) have investigated AIN single crystal growth by the sublimation method devised by Slack and McNelly (12) in order to produce substrates for GaN-based diodes. They reported that the morphology of AIN crystals depended on the sublimation temperatures. 

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