Siddha Pimputkar, Paul Von Dollen, Thomas Malkowski, Steven Griffiths,
Andrew Espenlaub, Sooyoung Moon, James S.Speck, Shuji Nakamura
Growth of large area, bulk gallium nitride (GaN) single crystals is of interest due to its wide spread application as a substrate for optoelectronic and electronic devices. Commercially available GaN substrates are currently grown using hydride vapor phase epitaxial (HVPE) methods, providing 2-inch diameter c-plane oriented substrates with threading dislocation (TD) densities of 106—108 cm-2 and c-plane lattice curvatures < 10 m. To further improve device performance and longevity, lower TD density material with flatter lattice planes are needed – in addition to large area non-polar and semi-polar substrates. A viable pathway to achieve these targets is the ammonothermal method.
This talk will provide an overview of bulk, single crystal GaN growth, with a particular focus on the basic ammonothermal method. Recent advances in our understanding of the basic ammonothermal growth environment, including the equilibrium concentration of ammonia present at typical growth conditions (P ~ 250 MPa, T ~ 600 ºC), will be presented and their significance in improving the method will be highlighted. Improvements in growth rate and purity due to the introduction of a silver capsule within a traditional Ni-Cr superalloy autoclave will be demonstrated.