DOPING OF AMORPHOUS-SILICON BY POTASSIUM-ION IMPLANTATION

Highly efficient n-type doping of hydrogenated amorphous silicon films has been achieved by ion implantation of potassium. A high dark conductivity, after implantation and annealing at the optimal temperature, could be obtained over the entire range of concentrations investigated (1018-4 × 1020cm-3). Post-hydrogenation with a Kaufmann ion source produced an increase in conductivity by a factor of up to four. The effect is opposite to that found in phosphorus-implanted samples, in which a decrease in dark conductivity after post-hydrogenation was observed. The highest conductivity obtained without microcry-stallization of the film was 1·6 × 10-l ?-1 cm-1. The conductivities of potassium-doped samples were higher than those of phosphorus-implanted samples by two orders of magnitude at high concentrations and four orders of magnitude at Iow concentrations. Thermal equilibration experiments were carried out on both annealed and post-hydrogenated samples which confirmed that the eauilibration behaviour of these interstitially doped films is analogous to that of substitutionally doped samples even though the mechanism of dopant activation and deactivation is different.