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Dynamics of charge carrier trapping in NO 2 sensors based on ZnO field-effect transistors

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Author: Andringa, A.-M. · Vlietstra, N. · Smits, E.C.P. · Spijkman, M.-J. · Gomes, H.L. · Klootwijk, J.H. · Blom, P.W.M. · Leeuw, D.M. de
Source:Sensors and Actuators, B: Chemical, 171-172, 1172-1179
Identifier: 462984
Keywords: Electronics · Activation energy · Charge carrier trapping · Field-effect transistor · NO 2 sensors · Stretched-exponential · Thermally stimulated current · Threshold voltage shift · Analytical description · Characteristic temperature · Charge carrier trapping · De-trapping · Functional dependence · Nitrogen dioxides · Operating temperature · Pressure window · Real time sensors · Sensor response · Stretched-exponential · Temporal behavior · Thermally activated · Thermally stimulated current · Threshold voltage shifts · Time dependence · Trap depth · ZnO · Activation energy · Charge carriers · Charge trapping · Dynamics · Field effect transistors · Optimization · Sensors · Thermoluminescence · Threshold voltage · Zinc oxide · Nitrogen oxides · Industrial Innovation · Mechatronics, Mechanics & Materials · HOL - Holst · TS - Technical Sciences


Nitrogen dioxide (NO 2) detection with ZnO field-effect transistors is based on charge carrier trapping. Here we investigate the dynamics of charge trapping and recovery as a function of temperature by monitoring the threshold voltage shift. The threshold voltage shifts follow a stretched-exponential time dependence with thermally activated relaxation times. We find an activation energy of 0.1 eV for trapping and 1.2 eV for detrapping. The attempt-to-escape frequency and characteristic temperature have been determined as 1 Hz and 960 K for charge trapping and 10 11 Hz and 750 K for recovery, respectively. Thermally stimulated current measurements confirm the presence of trapped charge carriers with a trap depth of around 1 eV. The obtained functional dependence is used as input for an analytical model that predicts the sensor's temporal behavior. The model is experimentally verified and a real-time sensor has been developed. The perfect agreement between predicted and measured sensor response validates the methodology developed. The analytical description can be used to optimize the driving protocol. By adjusting the operating temperature and the duration of charging and resetting, the response time can be optimized and the sensitivity can be maximized for the desired partial NO 2 pressure window. © 2012 Elsevier B.V. All rights reserved.