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 (∼104) and are analyzed in detail. The temperature-dependent I-V characteristics can be explained by assuming a lateral fluctuation σ=134±5meV of the mean barrier height ΦB,m=1.16eV. 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 EC-100 meV (E1) and EC-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.