title: Bipolar charge storage characteristics in copper and cobalt co-doped zinc oxide (ZnO) thin film.
abstract: The bipolar charge phenomenon in Cu and Co co-doped zinc oxide (ZnO) film samples has been studied using scanning probe microscopy (SPM) techniques. Those ZnO samples are made using a pulsed laser deposition (PLD) technique. It is found that the addition of Cu and Co dopants suppresses the electron density in ZnO and causes a significant change in the work function (Fermi level) value of the ZnO film; this results in the ohmic nature of the contact between the electrode (probe tip) and codoped sample, whereas this contact exhibits a Schottky nature in the undoped and single-element-doped samples. These results are verified by Kelvin probe force microscopy (KPFM) and ultraviolet photoelectron spectroscopy (UPS) measurements. It is also found that the co-doping (Cu and Co) can stabilize the bipolar charge, whereas Cu doping only stabilizes the positive charge in ZnO thin films.
authors.affiliation: Department of Mechanical Engineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576.
authors.forename: Amit
authors.initials: A
authors.lastname: Kumar
authors.forename: Tun Seng
authors.initials: TS
authors.lastname: Herng
authors.forename: Kaiyang
authors.initials: K
authors.lastname: Zeng
authors.forename: Jun
authors.initials: J
authors.lastname: Ding