An EXAFS and XANES study of MBE grown Cu-doped ZnO

The wide bandgap semiconductor, ZnO, is intrinsically n-type and one of the remaining hurdles to be overcome before it can be used for optoelectronic applications is achieving p-type doping. A potential candidate for a p-type dopant is Cu. Towards this end, X-ray near-edge absorption (XANES) has been used to determine changes in valency of Cu in molecular beam epitaxial grown ZnO as a function of growth parameters. Growth parameters varied include the Cu flux which was varied over roughly three orders of magnitude T-Cu = 800-1000 degreesC and two substrate temperatures: 300 and 600 degreesC. XANES measurements confirmed that Cu was in the +1 valence state for all as-grown samples. Preliminary EXAFS measurements also demonstrated that Cu incorporated into a Zn-atom position substitutionally. X-ray diffraction also indicated significant phase separation with the presence of both metallic Cu and CuO indicated for Cu concentrations > 3 x 10(21) cm(-3). (C) 2002 Elsevier Science B.V. All rights reserved.