Schottky-barrier heights of single-crystalNiSi2on Si(111): The effect of a surfacep-njunction

Abstract

Current-voltage, capacitance-voltage, and activation-energy measurements obtained for epitaxial nickel silicides grown on Si(111) have exposed the importance of the temperature used to flash-evaporate oxide off the surface prior to metal deposition. Near-ideal behavior is found for Schottky barriers grown on substrates cleaned at ∼820 °C in ultrahigh vacuum. The Fermi-level positions at the interfaces of single-crystal type-A and type-B ${\mathrm{NiSi}}_2$ are shown to differ by greater than 100 meV. Transmission electron microscopy demonstrated the epitaxial perfection of these silicide layers. At a cleaning temperature of 1050 °C, the apparent Schottky-barrier heights increased substantially for substrates with a doping concentration of $N_D$ less than approximately ${10}^{15}$ ${\mathrm{cm}}^{\mathrm{-}3}$. This increase is due to the conversion of the n-type semiconductor surface region to p type during the 1050 °C anneal. The presence of this p-n junction results in a high apparent Schottky-barrier height (≳0.75 eV) which no longer bears an immediate relationship to the interface Fermi-level position. Recent discrepancies reported by different groups concerning the barrier heights of ${\mathrm{NiSi}}_2$ on Si(111) are attributed to this effect.