Electrical properties of ZnO thin films and optical properties of ZnO-based nanostructures

We have grown ZnO thin films and nanopillars using pulsed laser deposition. Semi-insulating and n-conducting layers of various types can be fabricated. High-quality Pd Schottky contacts on the thin films have a high rectification ratio (similar to 10(4)) and are analyzed in detail. The temperature-dependent I-V characteristics can be explained by assuming a lateral fluctuation sigma=134 +/- 5 meV of the mean barrier height Phi(B,m)=1.16 eV. The dominating shallow donor is found to be Al. A degenerately doped ZnO:Al back-contact allows depletion layer spectroscopy up to 10 MHz. In our thin films, deep donor levels at E-C-100 meV (E1) and E-C-300 meV (E3) are found. The optical modes in ZnO nanopillars with hexagonal cross-section and various widths are found to be whispering gallery modes (WGM). Experimental spectra from polarization-resolved microphotoluminescence and theoretical simulations agree very closely without adjustable parameters. The comparison of TE and TM modes allows us to determine the birefringence in single nanopillars. (C) 2005 Elsevier Ltd. All rights reserved.