Superior surface modification layer of poly(styrene) on SiO$_2$ gate insulator in rubrene single crystal field-effect transistor

TL;DR

This study compares the effectiveness of different polymeric surface modification layers on SiO$_2$ insulators in rubrene single crystal FETs, highlighting poly(styrene)'s superior ambipolar carrier transport performance.

Contribution

It introduces a comparative analysis of polymeric protection layers, demonstrating poly(styrene)'s enhanced ambipolar transport in rubrene FETs over traditional materials.

Findings

Poly(styrene) provides the most balanced ambipolar carrier transport.

Poly(styrene) outperforms PMMA in FET performance.

Carrier trap density is lower with poly(styrene) coating.

Abstract

We conduct comparative research on the density of states of electron- and hole- carrier trap levels (DTR(E)), dispersing inside the energy gap of a rubrene single crystal in a field effect transistor (FET) struction with Ca and Au hetero-electrodes for an ambipolar carrier injection mode, by using polymeric protection-layer materials on a Si substrate. Three different types of polymeric materials, poly(methyl-methacrylate) (PMMA), poly(styrene) (PS) and poly(chloro-styrene) (PCS) are employed. From the temperature (T)-dependent source-drain current and gate voltage (ISD-VG) transfer characteristics, the values of DTR(E) are evaluated. PS exhibits the most efficiently-balanced ambipolar carrier transport, which is superior to PMMA that is most typically used as the standard protection layer on a SiO$_2$/doped-Si substrate. Discussions are made in the framework of a carrier multiple trap and release (CMTR) model.