Development of Commercially Viable Growth Rates for Bulk

We propose to develop AlN substrates for III-nitride epitaxy which will be superior to all substrates currently available commercially. In particular, the AlN substrates have significantly superior chemical compatibility, lattice/crystal structure match, thermal expansion match, and thermal conductivity when compared to sapphire substrates that are currently being extensively used for epitaxial growth. Production of bulk crystals of AlN will be easier than production of GaN or InN crystals due to the higher crystal growth rates possible for comparable nitrogen pressures. In addition, the higher thermal conductivity, larger band-gap energy and higher thermal stability of AlN will be attractive for many nitride applications. Our approach to bulk AlN crystal growth will be based on the sublimation- recondensation technique first developed for this material by Slack and McNelly. However, a significant reduction in the cost of individual substrates could be achieved if the growth rate is increased from the 0.3 mm/hr demonstrated in Slack's prior work. Here we propose to develop techniques to increase the growth rate to over 1 mm/hr based on our prior studies of the growth kinetics. In addition, we will demonstrate an appropriate substrate polishing technique during Phase I of this proposal using our existing AlN substrates.