Properties Of Centimeter-long ZnO Whiskers Prepared By Thermal Evaporation Of ZnO Powders

As a compound semiconductor with the band-width of 3.37eV and the exiton binding energe of 60meV at room temperature. ZnO has many potential applications in short-wavelength optoelectronic devices, including light emitting diodes(LEDs), laser diodes(LDs), ultraviolet detectors, high frequency and high power devices etc. There are only several laboratories abroad that have the capability to produce bulk-quality ZnO single-crystal in the world and no domestic report about preparation of bulk-quality ZnO single-crystal was published. Centimeter-long ZnO Whiskers have been prepared by our team with the simple technique of the reductant-enhanced thermal evaporation of ZnO powders.The ZnO whiskers prepared in graphite crucible were characterized by SEM (Scanning Electron Microscopy) , TEM (Transparent Electron Microscopy), SAED ( Selected Area Electron Diffraction) and XRD(X-Ray Diffraction) at first. These whiskers are single crystal and have the hexagonal wurtzite structure, the average length of 2cm with the range of 1 -4cm and the average diameter of 15μm with the range of 5-20μm. Then Carbon powders were employed as reductant and the result shows Carbon powders have the same reduction as well as griphte crucible. So a kind of reductant with excellent property and low price was found and can be used in the large-scale manufacture of ZnO in the future. The growth of ZnO whiskers is determined mainly by two considerations: one is the supersaturation of ZnO above the substrates, and the other is the crystallization habit of ZnO material itself. The supersaturation of ZnO above the substrats can be determined by controlling the concentration of Zn vapor above substrates and the grads of temperature between resource and substrates. The morphology of ZnO whiskers were affected by the ratio of ZnO:C and the cooling mechanism. Under the condition of the ZnO:C in the ratio of 1:2 and the air cooling mechanism, the ZnO whiskers with the desired quality were obtained.Room-temperature photoluminescence(PL) measurement were carried out to characterize the optical properties of ZnO whiskers using an excitation wavelenghth of 325nm. Only a narrow and strong excition that corresponds to the near band-edge emission is observed at 377nm and illuminates the ZnOwhiskers have good crystallinity and few defects. In addition, these ZnO whiskers are of voltage-dependent characteristic. They have high resistance properties under low voltage (9V), and the measured value is infinite. Under high voltage (600V) their resistance decreases dramatically and the measured resistance is 4.6x10"3I>cm.