The effect of ion bombardment on some properties of a-Si 0.8Ge 0.2:H alloys prepared by ion beam-assited reactive evaporation

Abstract

Amorphous hydrogenated silicon germanium thin films with 20% Ge content (a-Si 0.8Ge 0.2:H) were deposited by ion beam-assisted deposition (IBAD), using SiH 4 as the source gas. Moderate ion energies of ∼ 125 to 135 eV and an ion-to-atom ratio of ∼1, produced samples with a reduced number of SiH 2 and (SiH 2) n bonding configurations, an increased hydrogen content and a decreased porosity compared with non-bombarded samples. This reduces the disorder in the a-SiGe network as well as the defect density. The preferential attachment coefficient for these films is near unity. The optical and electrical properties of the a-SiGe:H alloy have been studied as a function of the ion beam energy and the ion-to atom ratio at the substrate. The best films had a photosensitivity of σ ph σ d = 1.7 × 10 4 and E g = 1.65 eV. The ion beam increased the optical gap, lowers the dark conductivity and increases the electrical activation energy.