Metalorganic chemical vapor deposition of ZnO(0001) thin films on GaN(0001) templates and ZnO(0001) substrates

We investigated the properties of ZnO layers grown by metalorganic chemical vapor deposition on GaN(0001) templates and ZnO(0001) bulk substrates. Steps and hexagonal pits were observed on the surfaces of the ZnO/GaN films as revealed by atomic force microscopy. The root-mean-square roughness was 2.6 nm over 20×20 mm2. The surfaces of the homoepitaxially grown ZnO films were smooth and featureless with a rootmean-square roughnesses of 0.12 nm over 6×6 mm2. Full width at half maximums of ω-scans for the on-axis (0002) and the off-axis (201) reflections were 0.091° and 0.159°, respectively. The corresponding values for the ZnO/ZnO films were 0.025° and 0.035°, respectively. Reciprocal space maps for the (105) reflection revealed that the ZnO films grown on GaN were fully relaxed and that the peaks of the homoepitaxially grown ZnO layers were indistinguishable from the ZnO substrate peaks. Ga-doped ZnO layers were grown at 300 °C on (In,Ga)N light emitting diodes as transparent electrodes and for wafer bonding to ZnO substrates in order to enhance the light extraction. The forward voltage was 4.5 V at 20 mA. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)