Electro-, photo- and scanning tunneling-luminescence studies of efficient light-emitting porous silicon

Porous silicon films as used in efficient blue-green electroluminescent dev ices (internal efficiency about 0.1%) were studied by scanning tunneling mi croscopy light emission spectroscopy (STMLES) as well as photoluminescence (PL) and electroluminescence (EL) spectroscopy. Areas of the n-type porous Si surfaces with small particles of about 5 nm dimensions gave STMLE, but a reas with larger structures gave no emission. Clear STMLE spectra gave a pe ak at 630 nm, quite different from the EL peak at 500 nm. Whereas the PL pe ak at 700 nm was consistent with the STM indication of quantised entities, the EL seemed more readily explicable in terms of defects at the metal cont act barrier.