THE FABRICATION AND CHARACTERIZATION OF NICKEL-OXIDE FILMS AND THEIR APPLICATION AS CONTACTS TO POLYMER POROUS SILICON ELECTROLUMINESCENT DEVICES/

Porous silicon electroluminescent devices have been fabricated from n- type substrates using indium tin oxide, hole-transporting poly(9-vinyl carbazole) and p-type nickel oxide films as hole injecting contacts. The addition of the polymer layer, which increases the contact area by penetrating into the porous microstructure, leads to an increase in t he device quantum efficiency of two orders of magnitude. The replaceme nt of indium tin oxide by nickel oxide, formed by a thermal evaporatio n process, lowers the device switch-on voltage from 55-60 V to 10-15 V . The p-type nature of the nickel oxide film allows holes to be inject ed from the valence band of the contact, and hence at a lower applied voltage than that required for indium tin oxide contacts. The luminesc ence power output from both devices is similar, and we suggest that th e limiting factor in the luminescent output is the rate of carrier flo w throughout the device nanostructures.