The defect structure of hydrogenated amorphous Si thin-films was studied by positron annihilation spectroscopy, whereas the density of states below the Fermi level was measured by constant photocurrent method. Divacancies and large vacancy clusters were identified as the main defects present in these films, with relative concentrations strongly dependent on the rf-power. Correlation between positron annihilation spectroscopy, constant photocurrent method results and I(V) characteristics of solar cells suggested the creation of energy levels above the Fermi energy, not observable by constant photocurrent method, related to large vacancy clusters.

Positron Annihilation and Constant Photocurrent Method Measurements on a-Si:H Films - a Comparative Approach to Defect Identification. P.M.Gordo, M.F.F.Marques, C.L.Gil, A.P.de Lima, G.Lavareda, C.N.de Carvalho, A.Amaral, Z.Kajcsos: Radiation Physics and Chemistry, 2007, 76[2], 220-3