Hole mobility in organic single crystals measured by a "flip-crystal" field-effect technique

TL;DR

This paper introduces a novel 'flip-crystal' method for fabricating high-mobility organic single-crystal FETs, minimizing damage and enabling accurate measurement of intrinsic charge transport properties.

Contribution

The study presents a new 'flip-crystal' technique that improves device quality and allows precise extraction of intrinsic and contact resistances in organic single-crystal FETs.

Findings

Achieved hole mobilities of 10.7, 1.3, and 1.4 cm^2/Vs for rubrene, tetracene, and pentacene.

The method reduces crystal handling damage and improves reproducibility.

Four-terminal measurements enable separation of channel and contact resistances.

Abstract

We report on single crystal high mobility organic field-effect transistors (OFETs) prepared on prefabricated substrates using a "flip-crystal" approach. This method minimizes crystal handling and avoids direct processing of the crystal that may degrade the FET electrical characteristics. A chemical treatment process for the substrate ensures a reproducible device quality. With limited purification of the starting materials, hole mobilities of 10.7, 1.3, and 1.4 cm^2/Vs have been measured on rubrene, tetracene, and pentacene single crystals, respectively. Four-terminal measurements allow for the extraction of the "intrinsic" transistor channel resistance and the parasitic series contact resistances. The technique employed in this study shows potential as a general method for studying charge transport in field-accumulated carrier channels near the surface of organic single crystals.