High efficiency blue–green electroluminescence and scanning tunneling microscopy studies of porous silicon

Schottky barrier porous silicon diodes have been fabricated showing electroluminescence peaking at 500 nm, with an internal efficiency for blue–green emission of about 0.1%. The structures, on low-resistivity n-type silicon, operate in reverse bias. Scanning tip light emission measurements show a peak emission at 630 nm, closer to that of photoluminescence from the identical surface at 700 nm than that of the electroluminescence. The latter is concluded to arise from nonquantum effects, at the metal interface. The threshold for visible light emission is at 0.2 mA/cm2, and for infrared light is an order of 10 higher. The lifetime in air is short when unencapsulated, but longer in vacuum.