Poole-Frenkel excitations

The thickness of PS layer is also one of the factors that influence the contact behavior. As thin PS layer show rectifying characteristics while thick PS layer show an almost symmetric one, Ben-Chorin (Ben-Chorin et al. 1994) proposed that the rectifying barrier is at the interface between PS and the doped substrate. It was also suggested by them (Ben-Chorin et al. 1994) that the usual diode structure formed by a metal contact, a PS layer, and a doped substrate can be visualized as a series combination of a voltage-dependent resistance and a rectifying barrier. Their study shows that the temperature- and voltage-dependent conductivity relationship follows Poole-Frenkel (PF)-t3 e conduction, where transport mechanism in high fields involves field-enhanced thermal excitation from Coulombic traps ... 

Fig. 5 Schematic representation of photo excitation processes in an n-type oxide film (a) localized state to localized state, (b) localized state to conduction band, (c) valence band to localized state, (d) excitation to localized state followed by escape to conduction band by Poole-Frenkel effect, (e) excitation to localized state followed by electron tunneling into the electrolyte.

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