Anomalous capacitance change in low-temperature grown ZnO thin-film transistors

Department of Electrical and Computer Engineering, Ajou University, Suwon, 443-749, Korea

Corresponding author: jungyol@ajou.ac.kr

Received: 21 February 2010
Revised: 9 May 2010
Accepted: 23 July 2010
Published online: 17 September 2010

Abstract

We studied capacitance-voltage characteristics of ZnO thin-film transistors (TFT's), grown by metalorganic chemical vapor deposition (MOCVD). We compared two ZnO TFT's: one grown at 450 °C and the other at 350 °C. ZnO grown at 450 °C showed smooth capacitance profile with electron density of 1.5×10²⁰ cm^-3. In contrast, ZnO grown at 350 °C showed a capacitance jump when gate voltage was changed to negative voltages. Current-voltage characteristics measured in the two samples did not show much difference. We explain that the capacitance jump is related to p-type ZnO layer formed at the SiO₂ interface. Current-voltage and capacitance-voltage data support that our ZnO films have anisotropic conductivity.