Characteristics of Surface-Emitting Cold Cathode Based on Porous Polysilicon

It is demonstrated that porous polysilicon (PPS) diode fabricated on the silicon substrate operates as efficient and stable surface-emitting cold cathode. A 1.5 pm of non-doped polysilicon layer is formed on n-type (100) silicon wafer and anodised in a solution of HF(50%): ethanol = 1:1 at a current density of 10 mA/cm2 for 30 seconds under illumination by a 500W tungsten lamp from a distance of 20 cm. Subsequently, PPS layer is oxidized in a rapid thermal oxidation(RTO) furnace for one hour at a temperature of 700°C. A semi-transparent 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 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/cm2 at 20V bias, and no fluctuation of emission current is observed as a function of time. Emission current is not affected by a surrounding pressure up to around 10 Pa. It is envisaged that mechanism of this emission is attributed to hot electron tunnelling.