Carrier injection, transport, and their effects on photoinduced dielectric breakdown in single crystalline paraffin (n-C36H74)

Abstract

Carrier injection and transport in single crystalline paraffin (n-C36H74) have been investigated on the basis of time-of-flight data and dc-photo injection experiments. The undoped, high-quality molecular crystal under study represents an isoelectronic analog to polyethylene. Charge-carrier mobilities in the range μ≤0.1 cm2 V−1 s−1 at room temperature have been recorded for both electrons and holes at moderate external electric fields. A clear correlation has been found between transport properties and the molecular structure. Regarding defect properties, significant differences have been observed for both types of carriers in the material. The presence of intrinsic deep traps is crucial to the transport properties of electrons and dominates the overall behavior of the material, but are virtually absent for injected holes. A decrease of the electron mobility with increasing external fields has been observed for electrons, while the opposite behavior has been found for injected holes. Photoinduced avalanching is largely due to a trap-enhanced field effect, as reported in the literature, where the massive injection of holes from the counter electrode is initiated above a critical external field.