Mechanism of efficient and stable surface-emitting cold cathode based on porous polycrystalline silicon films

It is demonstrated that a porous polysilicon (PPS) diode with a structure o f Au/PPS/n-type Si operates as an efficient stable surface-emitting cold ca thode. 1.5 mu m of an nondoped polysilicon layer is formed on an n-type (10 0) silicon wafer and anodized in a solution of HF (50%): ethanol = 1:1 at a current density of 10 mA/cm(2) for 30 s under illumination by a 500 W tung sten lamp from a distance of 20 cm. Subsequently, a PPS layer is oxidized i n a rapid thermal oxidation furnace for 1 h at a temperature of 700 degrees C. A semitransparent thin Au film (about 10 nm thick) is deposited onto th e PPS layer as a positive electrode and an ohmic contact is formed at the b ack side of the silicon wafer as a negative electrode. When a positive bias is applied to the Au electrode in vacuum, the diode uniformly emits electr ons. No electron emission is observed in the negatively biased region. Emis sion current is about 10(-4) A/cm(2) at a 20 V bias. It is further demonstr ated that electrons are quasiballistically emitted from a PPS diode due to a significantly reduced electron scattering in the PPS layer. As a result, the diode can emit fluctuation-free stable electron emission. The simplifie d model of emission and energy distribution of electrons are proposed and i t can explain the experimental results. (C) 1999 American Vacuum Society. [ S0734-211X(99)05003-9].