White electroluminescence from ITO/porous silicon junctions

A DC magnetron is used to sputter highly conductive ITO on the surface of porous silicon to form LEDs that not only emit the usual red-orange light in one bias direction, but stable white light when biased in the opposite direction. The direction of the bias required for white light emission depends on whether p- or n-type silicon is used. The white light is clearly visible to the naked eye and stable for >2 h of continuous operation. The likely source of the white light emission is from the intra- or inter-band transitions of hot carriers generated in an avalanche process.