Germanium implantation into amorphous silicon films

Abstract

The influence of the Ge + dose and post-implantation annealing on the dc dark-, photo conductivity and EPR of amorphous Si films have been investigated. Amorphous Si (a-Si) thin films have been deposited by evaporation. Doses ranged from 6 × 10 14 to 3 × 10 16 Ge cm −2 when increasing the Ge concentration to “critical” value (0.12-0.8 at.%) in a-Si and raising the annealing temperature to 400–450°C, a decrease of density of localized stated (DLS) was observed. It follows from the decrease of hopping conductivity contribution in dark conductivity as well as from the increase of photosensitivity σ photo σ dark up to 10 3 (AM1) and from the minimum-like dose dependence of spin density. We have found that B + and P + implantation into a-Si films predoped by 1.6 × 10 15 Ge cm −2 increased the dark conductivity in the 10 −9–10 −3 ω −1 cm −1 range, if samples were annealed at 400°C. The Fermi level location varied from ( E v + 0.2) to ( E c + 0.2) eV for the impurity valence respectively. Thus, a-Si with a critical concentration of Ge is similar to a-Si:H in its properties. The present results are discussed using the model of dangling bond self-saturation during random network structural relaxation that occurs due to Si and Ge atom size differences.