The covalent bond of gallium nitrid

The covalent bond of gallium nitride (GAN) is very large (E = 9.12ev / atom). The decomposition pressure at the melting point of 2500 ℃ is about 4.5GPa. When the decomposition pressure is lower than 4.5GPa, Gan will decompose directly without melting [11]. In order to make Gan stable at higher temperature, the pressure must be increased. Some typical equilibrium methods, such as Czochralski lifting method and Bridgman directional solidification method, are not suitable for the growth of GaN single crystal. At present, only some special methods can be used to produce long bulk single crystals. It mainly includes sublimation method [12], high temperature and high pressure method [13], melting crystallization method [14] and hydride gas phase epitaxy method [15, 16]. Among them, the first three methods have strict requirements on equipment and technology, and it is difficult to achieve large-scale single crystal, which can not meet the requirements of commercialization. The latter method, hydride vapor phase epitaxy (HVPE), is the mainstream of current research. Most of the homogeneous substrates that can be commercialized to provide Gan are produced by this method. [17, 18]. This technology has the advantages of simple equipment, low cost and fast growth speed. It can grow uniform and large-scale thick film as the substrate for further growth of device structure with MOCVD. At present, technology has become the most effective method for epitaxial thick films, and the grown thick films can be peeled off from the substrate by polishing or laser stripping, as the substrate of homoepitaxial further growth device structure [17, 18].