Highly efficient, spectrally pure 340 nm ultraviolet emission from Al _xGa1-xN nanowire based light emitting diodes

High crystal quality, vertically aligned Al_xGa1-xN nanowire based double heterojunction light emitting diodes (LEDs) are grown on Si substrate by molecular beam epitaxy. Such Al_xGa1-xN nanowires exhibit unique core-shell structures, which can significantly suppress surface nonradiative recombination. We successfully demonstrate highly efficient Al _xGa1-xN nanowire array based LEDs operating at ∼340 nm. Such nanowire devices exhibit superior electrical and optical performance, including an internal quantum efficiency of ∼59% at room temperature, a relatively small series resistance, highly stable emission characteristics, and the absence of efficiency droop under pulsed biasing conditions.