“…In 1992, Nakamura et al suggested a thermal annealing method above 700 • C [10], which is currently adopted by most chip makers to activate p-GaN layers. Since then, several modified methods have been suggested, such as KrF excimer-laser activation [11][12][13], multiple-step annealing [14], thermal annealing in an oxygen gas mixture [15], utilization of hydrogen-storage metal electrodes [16], and annealing with minority carrier injection [17,18]. Little achievement in hole concentration has been achieved by these methods, but these have basically not been suitable for mass production.…”