Multi-barrier field-emission behavior in PBTTT thin films at low temperatures.

Evan S H Kang,Eunseong Kim

doi:10.1038/srep08396

Evan S H Kang, Eunseong Kim

Open Access

https://doi.org/10.1038/srep08396

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Abstract

We investigated the low-temperature transport mechanism for poly[2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT). The temperature-dependent transport behavior was studied by varying the drain–source electric field and gate bias. The results suggest that low-temperature charge transport is dominated by direct tunneling at low electric fields, while field emission is prevailing for high electric fields with high carrier densities. However, the obtained barrier heights are remarkably greater than expected in a conventional field emission. We propose a simplified model of field emission through quasi-one-dimensional path with multiple barriers which shows good agreement with the results more clearly. Field emission across the domain boundaries may assist in overcoming the transport barriers induced by the interchain disorder, which results in the weak temperature dependence of conductivities and nonlinear current–voltage relation at low temperatures.

Highlights

The results suggest that low-temperature charge transport is dominated by direct tunneling at low electric fields, while field emission is prevailing for high electric fields with high carrier densities
Field emission across the domain boundaries may assist in overcoming the transport barriers induced by the interchain disorder, which results in the weak temperature dependence of conductivities and nonlinear current–voltage relation at low temperatures
We found that field emission is the dominant low-temperature transport mechanism at high carrier density and high electric fields, whereas direct tunneling is prominent at low fields

Summary

Introduction

We investigated the low-temperature transport mechanism for poly[2,5-bis(3-alkylthiophen2-yl)thieno(3,2-b)thiophene] (PBTTT). The results suggest that low-temperature charge transport is dominated by direct tunneling at low electric fields, while field emission is prevailing for high electric fields with high carrier densities. Yuen et al reported that the low-temperature transport in poly[2,5-bis(3-alkylthiophen-2-yl)thieno(3,2-b)thiophene] (PBTTT) at high carrier densities can be described by the one-dimensional (1d) Luttinger liquid (LL) theory, rather than in the framework of the classical transport theory[3]. We found that field emission is the dominant low-temperature transport mechanism at high carrier density and high electric fields, whereas direct tunneling is prominent at low fields. Assuming that the penetration of the series of quasi-domains becomes a dominant transport mechanism at high fields, we employ a simple model describing the field emission through multiple domain www.nature.com/scientificreports boundaries.

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