Effect of sulfur passivation of silicon (100) on Schottky barrier height: Surface states versus surface dipole

Aluminum and nickel contacts were prepared by evaporation on sulfur-passivated n - and p -type Si (100) substrates. The Schottky diodes were characterized by current-voltage, capacitance-voltage, and activation-energy measurements. Due to the passivation of Si dangling bonds by S, surface states are reduced to a great extent and Schottky barriers formed by Al and Ni on Si (100) substrates show greater sensitivity to their respective work functions. Aluminum, a low work function metal, shows a barrier height of <0.11 eV on S-passivated n -type Si (100) and ∼0.80 eV on S-passivated p -type Si (100), as compared to 0.56 and ∼0.66 eV for nonpassivated n - and p -type Si (100), respectively. Nickel, a high work function metal, shows ∼0.72 and ∼0.51 eV on S-passivated n and p -type Si (100), respectively, as compared to ∼0.61 and ∼0.54 eV on nonpassivated n and p -type Si (100), respectively. Though a surface dipole forms due to the adsorption of S on Si (100), our experimental results indicate that the effect of surface states is the dominant factor in controlling the Schottky barrier height in these metal-Si systems.