Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-Treatment
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Au/n-ZnO Rectifying Contacts Fabricated with Hydrogen Peroxide Pre-Treatment Qilin Gu1, Chi-Chung Ling1, Chor-Keung Cheung1, Jiaming Luo1, Xudong Chen1, Aleksandra Djurisic1, Gerhard Brauer2, Wolfgang Anwand2, Wolfgang Skorupa2, Helfried Reuther2, and Hock-Chun Ong3 1 Department of Physics, The University of Hong Kong, Hong Kong, China, People's Republic of 2 Institut f®πr Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf, Dresden, Germany 3 Department of Physics, The Chinese University of Hong Kong, Hong Kong, China, People's Republic of ABSTRACT Au contacts were fabricated on pressurized melted grown n-type ZnO single crystal samples pre-treated with boiling organic solvent and hydrogen peroxide. Contacts fabricated without any pre-treatment and with boiling organic solvent pre-treatment were found to have ohmic behavior. For the samples pre-treated with hydrogen peroxide, the Au contacts were found to have rectifying property. Systematic investigation was performed to study the dependence of the Schottky barrier height and the reverse bias leakage current on the temperature and the duration of the pre-treatment. Positron annihilation spectroscopy (PAS), Xray photoemission (XPS) and scanning electron microscope (SEM) were also used to understand how the vacancy type defect, contamination and surface morphology would influence the electrical property of the fabricated contacts. INTRODUCTION ZnO is a direct wide band gap semiconductor (with band gap ~3.3eV at 300K) that has recently attracted great deal of attention because of its many different potential applications in optoelectronic and spintronic fields.1-3 Although fabricating good quality Schottky contact is an essential step in developing ZnO device technology, there were relatively few literature reports on successful fabrication of rectifying metal contacts on ZnO.4-16 Surface pre-treatments on ZnO substrate like wet chemical etching (hydrogen peroxide, phosphoric acid and hydrochloric acid, etc.), ozone cleaning and plasma cleaning were reported to have the effects of improving the rectifying property of the fabricated metal/ZnO contact, or converting the fabricated metal/ZnO contact from ohmic to rectifying. With the aim to fabricate Schottky contact with low leakage current and ideality factor close to one, we have carried out a series of systematic investigation on how the H2O2 pretreatment would influence the rectifying properties of the fabricated Au/n-ZnO contacts. PAS, XPS and SEM studies were also performed to understand how the vacancy type defect, surface contamination and morphology would affect the electrical properties of the Au/n-ZnO contacts. EXPERIMENT The substrate used in the present study was melt grown undoped ZnO (0001) single crystal obtained from the Cermet Inc., U.S. The carrier concentration was measured to be
5×1016cm-3. The substrate was firstly cleaned by acetone, ethanol and then rinsed in de-ionized water. Large-area ohmic contact was then fabricated by depositing Al onto the substrate. The H
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