AVS 53rd International Symposium
    Electronic Materials and Processing Tuesday Sessions
       Session EM-TuM

Paper EM-TuM10
Carrier Dynamics of ZnO Thin Films - Degeneracy, Inhomogeneity and Multiple Carriers

Tuesday, November 14, 2006, 11:00 am, Room 2003

Session: Zinc Oxide
Presenter: W.C.T Lee, University of Canterbury, New Zealand
Authors: W.C.T Lee, University of Canterbury, New Zealand
C.H. Swartz, University of Canterbury, New Zealand
M. Cheung, University at Buffalo
A.N. Cartwright, University at Buffalo
S. Chandril, West Virginia University
T.H. Myers, West Virginia University
S.M. Durbin, University of Canterbury, New Zealand
Correspondent: Click to Email
Though mobility measured by conventional Hall effect systems has long been used as a figure of merit for the electronic quality of semiconductors, many factors such as multiple layers and inhomogeneity can affect the accuracy and validity of the technique. This is particularly true for ZnO thin films, where many studies report very low electron (and hole) mobility values. Thin films are complicated by degenerate interface layers arising from poor substrate wetting and/or low-temperature buffer layer. By varying the magnetic field strength and temperature in a Hall effect measurement system, it is possible to separate the different carriers. For example, where single-field Hall effect yields a mobility of less than 50 cm@super 2@/Vs for one molecular beam epitaxy (MBE) grown ZnO/sapphire sample, the variable field technique shows a low-mobility degenerate layer in parallel with a bulk layer having a mobility of 200 cm@super 2@/Vs, approaching the best reported bulk values. Another useful probe of electronic properties is time-resolved photoluminescence (TRPL), which yields carrier lifetime as a figure of merit. For samples with an electron concentration of 10@super 19@ cm@super -3@, a parabolic temperature dependence of carrier lifetime was observed, with a decrease in lifetime as the temperature increases from 14 K up to 150 K, followed by an increase for further increases in temperature. On the other hand, concentrations of 10@super 18@ cm@super -3@ yield lifetimes that increase monotonically as the temperature increases. Taken together, these two techniques offer a more detailed picture of the characteristics of the bulk film, which cannot be adequately evaluated by a simple single-field Hall effect measurement. This work is funded in parts by The MacDiarmid Institute for Advanced Materials and Nanotechnology, University of Canterbury and Tertiary Education Comission Doctoral Scholarship (W.C.T.L).