Admittance frequency dependence of Schottky barriers formed on dc triode sputtered amorphous silicon: Hydrogen influence on deep gap state characteristics

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Abstract
The admittance of Schottky diodes formed on dc triode sputtered amorphous hydrogenated silicon has been measured as a function of frequency at zero dc bias. The electrical behavior of the device is modeled with an equivalent circuit taking into account the thermal response time of gap states and the transport of carriers in the conduction band. The theoretical frequency dependence of the admittance of the Schottky diode is derived in two limiting cases: whether the occupancy of the gap states is controlled mainly by their interaction kinetics with the extended states or by the transport of electrons in the conduction band. We reach the conclusion that, in our samples, the response to an ac modulation is limited by the interaction kinetics of the localized states with the extended states of the conduction band. We apply this analysis to samples exposed to different sputtering conditions. The results show that, with these samples, not only the density of deep gap states at the Fermi level but also their efficiency for the capture of electrons decreases with hydrogen incorporation. These variations correlate well with the evolution of the electron mobility-lifetime product obtained from independent photoconductivity measurements.