THE EFFECT OF ION-BOMBARDMENT ON SOME PROPERTIES OF A-SI0.8GE0.2-H ALLOYS PREPARED BY ION-BEAM-ASSISTED REACTIVE EVAPORATION

Amorphous hydrogenated silicon germanium thin films with 20% Ge conten t (a-Si0.8Ge0.2:H) were deposited by ion beam-assisted deposition (IBA D), using SiH4 as the source gas. Moderate ion energies of similar to 125 to 135 eV and an ion-to-atom ratio of similar to 1, produced sampl es with a reduced number of SiH2 and (SiH2)(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 coefficien t 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 sigma(ph)/sigma(d) = 1.7 x 10(4) and E(g)= 1.65 eV. The ion beam increases the optical gap, lowers the dark conductiv ity and increases the electrical activation energy.