Various kinds of defect state distributions dominating electron trapping and recombination in a-Si:H films from different laboratories were studied by analyzing modulated photocurrent measurements obtained by varying the frequency or the bias light level. The characteristic features of the experimental modulated photocurrent spectra were compared with those predicted theoretically and a clear physical meaning was obtained. Two kinds of defect states were extracted directly from the spectra without prior assumptions about the form of the density of states. The energetic distributions of these defect states at the quasi-Fermi level and above it were calculated and their magnitude was found to differ by about an order of magnitude, while their capture coefficients differ by as much as 2 to 3 orders of magnitude. The 2 kinds of defect were attributed to Si dangling bonds with 3 back-bonded Si atoms and Si dangling bonds where one back-bond was replaced by H.

Various Defect States in a-Si:H Studied by Modulated Photoconductivity Spectroscopy. P.Kounavis: Physical Review B, 2002, 65[15], 155207 (9pp)