Enhancement of electrical and structural properties of GaN layers grown onvicinal-cut, a-plane sapphire substrates

We report the observation of significant enhancement in the electrical and crystalline properties of GaN layers grown on vicinally cut, a-plane sapphi re substrates. Room-temperature Hall mobility and x-ray rocking curve data show a nearly twofold improvement, independent of the processing conditions , for layers grown on substrates having vicinal angles of 1.5 degrees compa red to on-axis substrates. Transmission electron microscopy shows reduced e dge dislocation density and better alignment of the grains in layers grown on vicinally cut substrates. Preliminary photoluminescence measurements als o indicate pronounced differences in the yellow band spectra between the on -axis and off-axis cut substrates. These findings contrast the relatively m odest improvements observed in layers grown on c-plane substrates with vici nal angles as high as 10 degrees. [S0003-6951(98)00831-6].