This phenomenon is known as Poole-Frenkel effect .
It is well known that the classical Poole-Frenkel effect  concerns to the emission of a trapped charge from a single Coulomb trap to the conduction band in one-dimensional model.
So, the process of charge emission in our samples of PVK is bulk limited and seems to be governed by a mechanism like the Poole-Frenkel effect.
Victor Koldyaev and titled, "A Leakage Current Model for SOI based Floating Body Memory that Includes the Poole-Frenkel Effect
(PFE)," describes for the first time how the leakage current of SOI based floating body memory has been modeled and compared to experimental Z-RAM data, taking into account oxide/SOI Dit and PFE.
Ammar Nayfeh paper title: "A Leakage Current Model for SOI based Floating Body Memory that Includes the Poole-Frenkel Effect