The cold electron emission, characteristics of nanocrystalline porous polysilicon (PPS) diodes have been investigated for two PPS diodes prepared under different conditions. The origin of the difference in the emission efficiency and electron energy distribution between the two samples is analyzed in relation to the respective photoluminesccnce properties. The photoluminescence spectrum in the efficient electron emitter consists of red and blue emission bands corresponding to nanocrystalline silicon and interfacial oxide, respectively, while that in the low-efficiency emitter consists only of a blue band. Too much oxidation results in a reduction of the emission efficiency due to increased electron scattering. It is evident that both the formation of nanocrystalline silicon and its appropriate surface oxidation are key issues for obtaining efficient ballistic emission. These results are consistent with the emission model that electrons are accelerated in the PPS layer by multiple tunneling through interfacial oxide barriers between interconnected silicon nanocrystallites. (C) 2004 American Vacuum Society.