Effect of Impurities on Pentacene Thin Film Growth for Field-Effect Transistors

TL;DR

This study investigates how impurities, specifically pentacenequinone, affect the growth and electrical performance of pentacene thin films used in transistors, revealing impurity-induced changes in mobility and grain structure.

Contribution

It provides a detailed analysis of impurity effects on film morphology and electrical transport, highlighting the impact of impurity concentration on mobility and grain nucleation.

Findings

Mobility decreases fourfold at low impurity levels without morphological changes.

Impurities influence transport either as defects or at grain boundaries.

Higher impurity levels lead to smaller grains and further mobility reduction.

Abstract

Pentacenequinone (PnQ) impurities have been introduced into a pentacene source material at number densities from 0.001 to 0.474 to quantify the relative effects of impurity content and grain boundary structure on transport in pentacene thin-film transistors. Atomic force microscopy (AFM) and electrical measurements of top-contact pentacene thin-film transistors have been employed to directly correlate initial structure and final film structures, with the device mobility as a function of added impurity content. The results reveal a factor four decrease in mobility without significant changes in film morphology for source PnQ number fractions below ~0.008. For these low concentrations, the impurity thus directly influences transport, either as homogeneously distributed defects or by concentration at the otherwise-unchanged grain boundaries. For larger impurity concentrations, the continuing strong decrease in mobility is correlated with decreasing grain size, indicating an impurity-induced increase in the nucleation of grains during early stages of film growth.