Growth of Single Crystals and Fabrication of GaN and AlN Wafers

摘要

GaN thin films were grown on (0001) sapphire substrates at 1050 deg C by controlled evaporation of Ga metal and reaction with NH3. Transport of Ga species from source-to-substrate during this process and the influence of ammonia-liquid Ga reaction on Ga transport were investigated. Experimental results were compared to theoretical predictions to quantify the mechanism of transport in the vapor growth technique. In presence of NH3 Ga transport far exceeded the predicted upper limit for the vapor phase transport. Visual observations confirmed that a significant amount of Ga left the source in a cluster rather than atomic form. Pure N2 was flowed directly above the molten Ga source. This prevented direct contact and reaction between the molten Ga and NH3 and prevented Ga spattering and GaN crust formation on the source surface. It enhanced Ga evaporation rate and enabled control of Ga transport and V/III ratio in the system. The results showed that the process was mass transport limited and the maximum growth rate was controlled by transport of both Ga and reactive ammonia species to the substrate surface.