Wavelength-switchable ultraviolet light-emitting diodes.

Dual-wavelength ultraviolet light-emitting diodes (UV-LEDs) exhibiting two discrete emission peaks of comparable intensities are reported in this work. Furthermore, this is the first report where complete switching between these two peaks was achieved by simply changing the duty cycle of the pulsed-mode excitation. While earlier reports on dual-wavelength emission were based on complex multi-stage devices, our device layer-structure was nominally similar to single-wavelength LEDs, and the special properties were realized solely through the use of specifically designed AlGaN alloys. The molecular beam epitaxy (MBE) method was chosen for this work, which can operate at significantly wider growth-parameter ranges than other more commonly used techniques. The dual-wavelength nature of our LEDs was brought about by the deliberate incorporation of nanometer-scale alloy fluctuations in the quantum well based active regions by modulating the relative surface diffusion rates of Ga/Al adatoms. The wavelength selectivity was linked to the variation in thermally assisted carrier delocalization, transport, and subsequent recombination processes in regions of different compositional inhomogeneities.