Isothermal capacitance transient spectroscopy (ICTS) has been employed
to measure the energy dependence of the electron-capture cross sectio
n of continuously distributed defect levels in undoped a-Si:H film for
the first time, via the proposed novel structure. For undoped a-Si:H
films! experimental results show that the electron-capture cross secti
on of defect levels initially decreases exponentially, reaches a minim
um, and then increases exponentially with energy depth measured from t
he mobility edge of the conduction band. This v-shaped distribution of
the electron-capture cross section of continuously distributed defect
levels in undoped a-Si:H film is different from that in phosphorous-d
oped a-Si:H film. This means that mechanisms other than multiphonon em
ission can be dominant in the electron-capture process in the gap stat
es in undoped a-Si:H film.