Semiconductor surface and interface passivation by cyanide treatment

Cyanide treatment which simply involves immersion of semiconductors in cyanide solutions can passivate interface states as well as surface states. When Si surfaces are treated with KCN solutions, a surface photovoltage greatly increases, and the surface recombination velocity is calculated to be decreased from ∼3000 cm/s to less than 200 cm/s. When the cyanide treatment is applied to ultrathin SiO2/single-crystalline Si structure, interface states are passivated. The passivation of the SiO2/Si interface states increases the energy conversion efficiency of 〈indium tin oxide (ITO)/SiO2/Si〉 MOS solar cells to 16.2% and decreases the leakage current density for 〈aluminum (Al)/SiO2/Si〉 MOS diodes to 1/3–1/8. When the cyanide treatment is performed on polycrystalline (poly-) Si, defect states in Si up to at least 0.5 μm depth from the surface are passivated, resulting in a vast increase in the energy conversion efficiency of 〈ITO/SiO2/poly-Si〉 solar cells and a decrease in the dark current density of 〈Al/SiO2/poly-Si〉 MOS diodes to 1/100–1/15 that without cyanide treatment. The defect passivation is attributed to the formation of SiCN bonds from defect states. SiCN bonds are found not to be ruptured by heat treatment at 800 °C and AM 1.5 100 mW/cm2 irradiation for more than 1000 h. Density functional calculations show that the thermal and irradiation stability results from strong SiCN bonds with the bond energy of 4.5 eV. When the cyanide treatment is performed on oxide/GaAs(1 0 0) structure, the interface state density decreases to ∼50%. The cyanide treatment can also passivate defect states in Cu2O films, resulting in increases in the carrier density and the band-to-band photoluminescence intensity.