Effects of annealing in oxygen on electrical properties of AlGaN/GaN heterostructures grown on Si

We investigated the effects of oxygen annealing on electrical characteristics of AlGaN/GaN heterostructures grown on Si by metalorganic chemical vapor deposition. It was shown that such treatment suppresses parasitic tunneling leakage current due to surface states or dislocations, decreases the threshold voltage corresponding to depletion of the two-dimensional electron gas at the AlGaN interface, and increases the effective interdevice isolation resistance. The suppression of the leakage current is explained by oxygen passivation of the empty states at the surface of the AlGaN barrier. Oxygen diffusion along dislocations and passivation of dislocation related states also could play a role. The decreased threshold voltage is attributed to the increased concentration of possibly oxygen related deep traps near the AlGaN/GaN interface. The increase in the GaN buffer resistivity after annealing is ascribed to the annihilation of the 0.38 eV deep electron traps believed to be introduced at the surface of GaN during mesa formation by dry etching.