Field-induced charge transport at the surface of pentacene single crystals: a method to study charge dynamics of 2D electron systems in organic crystals

TL;DR

This paper introduces a method to measure surface charge transport in pentacene single crystals, revealing temperature-dependent mobility and insights into charge trapping mechanisms in organic crystals.

Contribution

A novel technique for injecting and measuring surface charge transport in organic crystals, minimizing damage and enabling detailed study of charge dynamics.

Findings

Surface mobility ranges from 0.1 to 0.5 cm^2/Vs

Mobility is temperature-independent above ~150 K

Mobility becomes thermally activated at lower temperatures

Abstract

A method has been developed to inject mobile charges at the surface of organic molecular crystals, and the DC transport of field-induced holes has been measured at the surface of pentacene single crystals. To minimize damage to the soft and fragile surface, the crystals are attached to a pre-fabricated substrate which incorporates a gate dielectric (SiO_2) and four probe pads. The surface mobility of the pentacene crystals ranges from 0.1 to 0.5 cm^2/Vs and is nearly temperature-independent above ~150 K, while it becomes thermally activated at lower temperatures when the induced charges become localized. Ruling out the influence of electric contacts and crystal grain boundaries, the results contribute to the microscopic understanding of trapping and detrapping mechanisms in organic molecular crystals.