  We present a hybrid light-emitting diode structure composed of an n-type
gallium nitride nanowire on a p-type silicon substrate in which current is
injected along the length of the nanowire. The device emits ultraviolet light
under both bias polarities. Tunnel-injection of holes from the p-type substrate
(under forward bias) and from the metal (under reverse bias) through thin
native oxide barriers consistently explains the observed electroluminescence
behaviour. This work shows that the standard p-n junction model is generally
not applicable to this kind of device structure.
