Realization of high-resistance GaN by controlling the annealing pressure of the nucleation layer in metal-organic chemical vapor deposition

The influence of the annealing pressure of the nucleation layer (NL) on the resistance of GaN films grown on sapphire by means of metal-organic chemical vapor deposition has been investigated. It is found that the sheet resistance of GaN increases significantly with decreasing the annealing pressure. When the annealing pressure is 10 kPa, GaN with sheet resistance higher than 1011 Ω/sq is achieved. It is determined that the edge-component threading dislocations (ETDs) rather than the screw-component ones are the dominant structural feature responsible for the resistance variation. Based on the analysis of in-situ reflectance and atomic force microscopy, it is believed that the island density and island size in the NL are the key factors accounting for the resistance variation in GaN. The high island density and small island size in the NL not only lead to more ETDs in GaN, which introduce more acceptors to compensate the background electrons, but also enhance the rapid coalescence in GaN and thus effectively limit the diffusion of oxygen impurities into GaN epilayers from GaN/sapphire interfaces.