Decrease in gap states at ultrathin SiO2/Si interfaces by crown-ether cyanide treatment

A simple method to passivate interface states at ultrathin ${\mathrm{SiO}}_{\mathrm{2}}\mathrm{/Si}$ interfaces is developed. In this method, ultrathin ${\mathrm{SiO}}_{\mathrm{2}}$ -covered Si is immersed in a KCN solution containing crown-ether, followed by a rinse in water at 25 °C. The conductance–voltage measurements show that the interface state density is decreased to ∼1/10 by this crown-ether cyanide treatment. The capacitance–voltage measurements show that contamination by ${\mathrm{K}}^{\mathrm{+}}$ ions is effectively avoided by the inclusion of crown-ether. These results demonstrate that crown-ether molecules effectively capture ${\mathrm{K}}^{\mathrm{+}}$ ions and consequently ${\mathrm{CN}}^{\mathrm{-}}$ ions effectively may react with defect states, probably forming Si–CN bonds. The passivation of interface states by the cyanide treatment improves the electrical characteristics of metal–oxide–semiconductor tunneling diodes.