Influence of Copper Dopants on the Resistivity of ZnOFilms

✍ Scribed by Hartmann, A.; Puchert, M. K.; Lamb, R. N.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 424 KB
• Volume: 24
• Category: Article
• ISSN: 0142-2421
• DOI: 10.1002/(sici)1096-9918(19960916)24:9<671::aid-sia165>3.0.co;2-d

✦ Synopsis

Copper 2p,,, x-ray photoemission spectroscopy (XPS) measurements and near-edge x-ray absorption spectroscopy (NEXAFS) studies of copperdoped ZnO thin films were carried out in order to understand the role of the dopants in increasing the 6lm resistivity. c-Axis-oriented ZnO films (thickness 120 nm) were deposited by r.f. sputtering on Cr-coated SiOJSi substrates and subsequently implanted with metallic copper (0.5 at.%). After implantation, XPS results indicated that the dopant consists of a mixture of Cu' and Cuo. The c-axis film resistivity was found to decrease to 7 x lo' Q,cm (prior to implantation: 5 x 10" Q, * cm). Oxygen annealing resulted in complete oxidation of the dopants in the film surface and bulk (Cuz+) as indicated by XPS and bulk-sensitive fluorescence NEXAFS. The film resistivity increased to 2 x 10" 51cm, which can be explained in terms of electron trapping by Cu 3d hole states of Cu". The NEXAFS results suggested that the copper dopants after oxygen annealing have preferred orientations in the ZnO matrix. Additional vacuum annealing reduced Cuz' ions to Cu', which demonstrated that the observed decrease in film resistivity from 2 x 101'-107 51-cm is due to the Cu' oxidation state.