Bulk growth of group III nitrides by the chemical vapor reaction process and the ammonothermal method

Single-crystalline GaN and AlN wafers are in strong demand to improve state-of-the-art III-Nitride optoelectronic and electronic devices. However, due to their high melting points and high equilibrium N2 over pressures at high temperatures, growth of bulk GaN and AlN is extremely challenging. Although free-standing GaN wafers fabricated by hydride vapor phase epitaxy (HVPE) are commercially available, vapor-phase growth in an open reactor is not cost effective to grow bulk GaN ingots. AlN ingots can be grown by the physical vapor transport (PVT) method; however, a vapor phase approach to grow semi-bulk AlN wafers must be developed until the PVT method overcomes multi-grain and impurity problems.; In this research, the chemical vapor reaction process (CVRP) of AlN and ammonothermal growth of GaN were investigated to present more cost-effective ways to realize III-Nitride wafers. It was shown that the CVRP is a competitive method to grow relatively thick films of AlN. The structural quality of AlN films was improved from AlN templates grown by metalorganic chemical vapor deposition. Growth on grooved sapphire resulted in AlN domains with their c-axis perpendicular to the sidewalls of the grooves. The top portion of these domains showed reduced dislocation density, as low as 8 x 108 cm-2.; The fundamental characteristics of so-called ammonothermal growth of GaN were studied. The effects of mineralizers on phase selection of GaN formation and solubility of GaN in supercritical ammonobasic solutions were investigated in detail. GaN films were successfully grown on GaN seed crystals via fluid transport of a Ga nutrient. A maximum thickness of 45 mum, a maximum growth rate of 88 mum/day, and a maximum growth area of 3 x 4 cm2 were demonstrated. A free-standing GaN platelet separated from a seed showed a featureless surface and threading dislocation density on the order of low-10 9 cm-2. Growth of GaN films from a polycrystalline GaN nutrient was also demonstrated, which solves a problem of the growth saturation caused by depletion of a Ga nutrient.