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Charge transport in amorphous InGaZnO thin-film transistors

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Author: Germs, W.C. · Adriaans, W.H. · Tripathi, A.K. · Roelofs, W.S.C. · Cobb, B. · Janssen, R.A.J. · Gelinck, G.H. · Kemerink, M.
Type:article
Date:2012
Source:Physical Review B - Condensed Matter and Materials Physics, 15, 86
Identifier: 465833
Article number: 155319
Keywords: Physics · High Tech Systems & Materials · Industrial Innovation · Mechatronics, Mechanics & Materials · HOL - Holst · TS - Technical Sciences

Abstract

We investigate the mechanism of charge transport in indium gallium zinc oxide (a-IGZO), an amorphous metal-oxide semiconductor. We measured the field-effect mobility and the Seebeck coefficient (S=ΔV/ΔT) of a-IGZO in thin-film transistors as a function of charge-carrier density for different temperatures. Using these transistors, we further employed a scanning Kelvin probe-based technique to determine the density of states of a-IGZO that is used as the basis for the modeling. After comparing two commonly used models, the band transport percolation model and a mobility edge model, we find that both cannot describe the full properties of the charge transport in the a-IGZO semiconductor. We, therefore, propose a model that extends the mobility edge model to allow for variable range hopping below the mobility edge. The extended mobility edge model gives a superior description of the experimental results. We show that the charge transport is dominated by variable range hopping below, rather than by bandlike transport above the mobility edge. © 2012 American Physical Society.