Lasing Characteristics of Nano-structured Zinc Oxide
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Lasing Characteristics of Nano-Structured Zinc Oxide Shou-Yi Kuo1, Wei-Chun Chen2, and Fang-I Lai3 1 Department of Electronic Engineering, Chang Gung University, 259 Wen-Hwa 1st Road, KweiShan Tao-Yuan,Taiwan,333, R.O.C, Tao-Yuan, 333, Taiwan 2 Instrument Technology Research Center, National Applied Research Laboratories, 20 R&D Road VI, Hsinchu Science Park, Hsinchu 300, Taiwan, Hsinchu, 300, Taiwan 3 Department of Electrical Engineering, Yuan-Ze University, 135, Far-East Rd., Chung-Li, Taoyuan, Taiwan, ROC, Tao-Yuan, 320, Taiwan
ABSTRACT Highy-quality nano-structured ZnO samples have been synthesized by simple chemical solution and post-thermal treatment. The samples were characterized by x-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), temperature-dependent photoluminescence (PL) spectra measurements. XRD patterns illustrated that there were no second phases in these ZnO samples, and the TEM results indicated that the ZnO samples are single crystalline with a hexagonal structure. Room-temperature PL spectra of ZnO thin films showed a strong UV near-band-edge (NBE) emission located at about 390 nm and a green defect-related (G) emissions, where the intensity ratio (INBE/IG) varies with the annealing temperatures. Meanwhile, the ZnO samples exhibited free exciton and very sharp exciton emissions at low temperatures. Particularly, room-temperature UV random lasing characteristic of ZnO films has been observed as well. It is shown that these nano-structured ZnO samples can exhibit random laser action depending on the growth condition. The threshold intensity for the lasing is comparable to earlier reported data. These results indicate that nanostructured ZnO samples prepared by simple techniques may be a promising material for further photonic devices. Possible lasing mechanism is discussed and further investigation to clarify the mechanism between the nano-structured ZnO samples is still underway.
INTRODUCTION Transparent conducting oxide layers have been studied extensively because of their broad range of application such as transparent electrodes in display and in photovoltaic devices. Amongst these TCO’s, zinc oxide (ZnO) is a very promising candidate for future thin-film technology, especially because of its low cost and because of the wide availability of its constituent raw materials.[1-3] Zinc oxide has been traditionally used in transparent conducting films, piezoelectric transducers, optical waveguides, varistors, acoustic wave devices and gas sensors. Especially, the large exciton binding energy at room temperature (~60 meV), which corresponds to 2.4 times the effective thermal energy at room temperature, ensures efficientultraviolet (UV) emission from the excitons. The significant binding energy can also be changed by changing structures. The stability of the exciton makes ZnO a promising material for the realization of excitonic laser gain at room temperature. The strong excitonic effect in ZnO is
expected to play an important role in t
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