Influence of different metallic contacts on porous silicon electroluminescence

We will present data about current-induced light emission from a solid state contact between porous silicon and a metal. The contact metal consists of a mixture of gold and a second metal, which are coevaporated onto the porous substrate. The quantum efficiency and the spectrum of the fabricated device strongly depend on the second metal used for deposition. The highest quantum efficiency is achieved by adding indium to the gold. The spectral peak positions are at 455 nm, 520 nm, 555 nm and 700 nm for indium, gallium, tin and antimony, respectively. The sample with pure gold emits at 530 nm. The electroluminescence is observed after first applying high reverse voltage and then switching into a.c. operation. A discussion on the origin of light emission is given in terms of defect centre luminescence in the oxide.