Amorphous-like Density of Gap States in Single Crystal Pentacene

TL;DR

This study reveals that highly purified single crystal pentacene exhibits amorphous-like density of gap states, with broader band tails than inorganic amorphous solids, affecting electronic properties near the dielectric interface.

Contribution

It introduces a method to measure the density of states in pentacene crystals and compares optical, electrical, and FET data to understand disorder effects.

Findings

Pentacene crystals have broader band tails than inorganic amorphous solids.

Gap state density is significantly higher within 5-10 nm of the dielectric interface.

Optical and electrical measurements can effectively characterize the density of states.

Abstract

We show that optical and electrical measurements on pentacene single crystals can be used to extract the density of states in the HOMO-LUMO bandgap. It is found that these highly purified crystals possess band tails broader than those typically observed in inorganic amorphous solids. Results on field effect transistors (FETs) fabricated from similar crystals are also compared. The FET data imply that the gap state density is much larger within 5-10 nm of the gate dielectric. These results are discussed in terms of both crystal phase domains and structural disorder mechanisms.