Electrical Study of Trapped Charges in Copper-Doped Zinc Oxide Films by Scanning Probe Microscopy for Nonvolatile Memory Applications.

Ting Su,Haifeng Zhang,Yogendra Kumar Mishra

doi:10.1371/journal.pone.0171050

Abstract

Charge trapping properties of electrons and holes in copper-doped zinc oxide (ZnO:Cu) films have been studied by scanning probe microscopy. We investigated the surface potential dependence on the voltage and duration applied to the copper-doped ZnO films by Kelvin probe force microscopy. It is found that the Fermi Level of the 8 at.% Cu-doped ZnO films shifted by 0.53 eV comparing to undoped ZnO films. This shift indicates significant change in the electronic structure and energy balance in Cu-doped ZnO films. The Fermi Level (work function) of zinc oxide films can be tuned by Cu doping, which are important for developing this functional material. In addition, Kelvin probe force microscopy measurements demonstrate that the nature of contact at Pt-coated tip/ZnO:Cu interface is changed from Schottky contact to Ohmic contact by increasing sufficient amount of Cu ions. The charge trapping property of the ZnO films enhance greatly by Cu doping (~10 at.%). The improved stable bipolar charge trapping properties indicate that copper-doped ZnO films are promising for nonvolatile memory applications.

Highlights

Ferroelectric thin films have attracted much attention due to their potential application of nonvolatile random-access-memory devices [1]
Original surface potential of the undoped zinc oxide (ZnO) and copper-doped ZnO film were measured before charge injection
The difference in the Kelvin probe force microscopy data can be understood in terms of the doping-induced shift of the Fermi level

Summary

Introduction

Ferroelectric thin films have attracted much attention due to their potential application of nonvolatile random-access-memory devices [1]. Copper-doped ZnO is one of the most promising because its excellent versatility in electrical properties [2,3]. Mishra et al [4,5] successfully reported direct growth of freestanding ZnO tetrapod networks for multifunctional applications. Tiwari et al [6] reported the observation of room temperature ferromagnetism in Cu-doped ZnO films, which are very important findings. The electrical property of the ZnO film is dominated by doped atom incorporated during production and growth processes. An efficient way of improving the properties of ZnO films is the addition of certain dopants. Kumar et al [7,8] reported tailoring of extrinsic dopants provide interesting enhancement in electronic transport properties of ZnO films. The interesting features of ZnO:Cu have inspired us to PLOS ONE | DOI:10.1371/journal.pone.0171050 January 30, 2017

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Results

Conclusion