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 of Au/PPS/n-type Si operates as an efficient stable surface-emitting cold cathode. 1.5 mu m of an nondoped polysilicon layer is formed on an n-type (100) 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 tungsten lamp from a distance of 20 cm. Subsequently, a PPS layer is oxidized in 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 the PPS layer as a positive electrode and an ohmic contact is formed at the back 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 electrons. No electron emission is observed in the negatively biased region. Emission current is about 10(-4) A/cm(2) at a 20 V bias. It is further demonstrated 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 simplified model of emission and energy distribution of electrons are proposed and it can explain the experimental results. (C) 1999 American Vacuum Society. [S0734-211X(99)05003-9].