Emission, Defects and Structure of ZnO Nanocrystals obtained by Electrochemical method
- PDF / 822,255 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 61 Downloads / 201 Views
Emission, Defects and Structure of ZnO Nanocrystals obtained by Electrochemical method Tetyana Torchynska1,* Brahim El Filali2, Georgiy Polupan3 and Lyudmula Shcherbyna4 1
Instituto Politécnico Nacional, ESFM, México D.F.07738, MEXICO Instituto Politécnico Nacional, UPIITA, México D.F.07320, MEXICO 3 Instituto Politécnico Nacional, ESIME, México D.F.07738, MEXICO 4 V. Lashkaryov Institute of Semiconductor Physics at NASU, Kyiv, 03028, UKRAINE 2
ABSTRACT The impact of different annealing temperatures on the crystal structure, emission and radiative defects in ZnO nanocrystals (NCs) has been investigated by means of the scanning electron microscopy (SEM), Energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and photoluminescence (PL) techniques. ZnO NCs were prepared by the anodization of zinc sheets in an electrolyte and thermal annealed at the various temperatures: 200, 240, 280, 320, 360 and 400oC for two hours in ambient air. The XRD study indicates that ZnO NCs are characterized by the hexagonal wurtzite structure. The study of annealing temperature impact on the morphology of ZnO NCs has shown that the NC size enlarges and the film crystallinity improves with increasing annealing temperatures from 200oC up to 400oC. But in the temperature range of 360-400oC the dissolution of oxygen atoms raises essentially in ZnO NC films as it follows from EDS data. Simultaneously, the near band edge (NBE) emission intensity falls down, XRD parameters of ZnO NCs change and the intensity of defect related orange and green PL bands increases owing to increasing the defect concentrations. The optimal temperatures for the ZnO NC oxidation, together with keeping the high NBE emission intensity, are estimated as 360 oC. The nature of native defects responsible for orange and green emissions in ZnO NCs has been discussed. INTRODUCTION Zinc oxide nanocrystals (NCs) have been attracted enormous attention in the last two decades owing to their exceptional physical properties that promises a great variety of applications in optoelectronics and photonics. ZnO NCs are characterized by more elevated chemical and thermal stability, a wide direct band gap of 3.37eV and large exciton binding energy of 60meV at 300K, non-toxicity and its low price [1]. Other advantages of ZnO NCs are related to interesting electro-optic [2], piezoelectric [3], electromechanical and magnetic [4,5] properties. ZnO is a promising semiconductor for higher temperature applications such as: thin film transistors, UV lasers, white light emitting diodes, acoustic devices, biomedical sensors, actuators, solar cells, devices of high data storage density, etc. [6,7]. Regardless on the deposition method used, the thermal annealing, as a rule, was applied to improving the ZnO film crystallinity after the film growth. Thermal annealing is accompanied by raising the ZnO NC sizes, increasing ZnO energy band gap and film transparency [8, 9]. The temperature for this annealing varies in a wide temperature range from 100-400oC [10] or 250550oC up to 650-900oC [8]. Unfo
Data Loading...
