Published online by Cambridge University Press: 26 February 2011
The energy distribution of localized states above the Fermi level in undoped a-Si:H and a-SiGe:H has been determined by phase shift analysis of modulated photocurrents. (1) A peak in the DOS with 0.56 – 0.65 eV activation energy has been found, reflecting the D− -state of isolated dangling bonds. A second peak with 0.35 eV activation energy has been detected which is attributed to the T3+-state of T3+-T3− -pairs or to the antibonding state of weak Si-Si bonds, respectively. Strong illumination raises the lower peak and quenches the upper one supporting a shallow state - deep state conversion model. (2) From temperature-dependent measurements a shift of the dominant electron transport path into the tail with decreasing temperature - associated with tail state hopping - has been obtained.