Properties of MIS capacitors using the atomic-layer-deposited ZnO semiconductor and Al(2)O(3) insulator

Abstract

This paper reports the fabrication and characterization of metal-insulator-semiconductor (MIS) capacitors using a ZnO semiconducting layer and Al(2)O(3) insulating layer deposited by plasma-enhanced atomic layer and thermal atomic layer deposition, respectively. The sample stack structure is Al(2)O(3)/ZnO/ITO. The effects of the ZnO deposition conditions, such as plasma power, film thickness, and oxygen flow rate, on the electrical characteristics of the MIS capacitors were investigated. The thicknesses of the ZnO and Al(2)O(3) layers were changed independently in order to examine the influence of full depletion of carriers on the capacitance -voltage (C-V) characteristics. It was found that the electrical properties of the ZnO thin films changed according to their thickness. This was attributed to a chemical interaction with the under-indium-tin-oxide (ITO) layers during the long growth time (over2 ), which made it difficult to determine the semiconductor parameters, such as the carrier density. During the process of Al(2)O(3) film deposition, an interfacial layer was grown between the ZnO and Al(2)O(3) films. This interfacial layer deteriorated the C-V characteristics of the MIS capacitors because of the interface state increment. It was found that there was a certain range of ZnO and Al(2)O(3) thicknesses where the optimal properties were achieved. (C) 2008 The Electrochemical Society.