An Overview of Gallium Nitride Substrate Materials Developments for Optoelectronic and Microelectronic Applications
The hydride vapor phase epitaxy technique has been used to grow bulk GaN crystals for processing into free-standing substrates for optoelectronic and micro-electronic applications. Substrates up to 2 inches in diameter were fabricated and tested for materials properties and device applications. Defect densities as low as 5x104 cm-2 were measured via CL imaging. Semi-insulating electrical behavior was achieved through Fe doping with room temperature resistivity measurements as high as 2×109 Ω·cm measured using COREMA. Schottky diodes with >600V breakdown voltage and 20 ns reverse recovery time were fabricated. AlGaN/GaN HEMTs were fabricated and tested, resulting in an output power density of 5.0 W/mm at 2 GHz with a power- added efficiency of 35% and an associated gain of 14.5 dB. This constitutes the first report of significant power density from MBE-grown HEMTs on free-standing HVPE GaN substrates.