Highly doped evaporated amorphous silicon by alkali implantation

Evaporated films of amorphous silicon can be doped interstitially by implantation of alkali ions. Room temperature conductivity values as high as σ=2×10−3 (Ω cm)−1 and activation energies of σ as low as 0.25 eV are obtained by implantation of 1% potassium in films prepared with a low rate of deposition. The doped state is stable up to 320 °C. Results from stepwise doping with sodium indicate a rather constant density of localized states in the gap of the order 3×1019/cm3 eV for rapidly evaporated films.