Abstract
The current-voltage characteristics of Ni contacts with the surfaces of ZnO thin films as well as single crystal (0001) ZnO substrate are investigated. The ZnO thin film shows a conversion from Ohmic to rectifying behavior when annealed at 800°C. Similar findings are also found on the Zn-polar surface of (0001) ZnO. The O-polar surface, however, only shows Ohmic behavior before and after annealing. The rectifying behavior observed on the Zn-polar and ZnO thin film surfaces is associated with the formation of nickel zinc oxide (Ni1-xZnxO, where x = 0.1, 0.2). The current-voltage characteristics suggest that a p-n junction is formed by Ni1-xZnxO (which is believed to be p-type) and ZnO (which is intrinsically n-type). The rectifying behavior for the ZnO thin film as a result of annealing suggests that its surface is Zn-terminated. Current-voltage measurements could possibly be used to determine the surface polarity of ZnO thin films.
Highlights
In recent years, development in optoelectronic devices using ZnO has attracted great interest as this semiconducting material has a wide bandgap (,3.4 eV), a high exciton binding energy (,60 meV) and a relatively non-toxic nature [1]
The Ni metallic layer is evaporated on the ZnO thin film as well as on both the Zn- and O-polar surfaces of the single crystal (0001) ZnO
The annealing temperature was chosen after considering the XRD data which indicated that as-deposited ZnO thin films annealed at 800uC experienced a decrease of,1.4% in the c lattice constant to values comparable to the strainfree lattice constant (,0.5205 nm)
Summary
Development in optoelectronic devices using ZnO has attracted great interest as this semiconducting material has a wide bandgap (,3.4 eV), a high exciton binding energy (,60 meV) and a relatively non-toxic nature [1]. The electrical behavior of metal contacts on the different surfaces of ZnO may exhibit Ohmic, near-linear or rectifying behavior.
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