DOI: 10.5176/2301-3516_OPAP16.14
Authors: W.Maryam, N.Fazrina, M.R. Hashim, M.M. Halim, H.C. Hsu
Abstract:
Strong scattering and gain in disordered zinc oxide (ZnO) materials leading to the formation of random lasing has been reported since the late 90’s [1], [2]. In the recent decade, random lasing have been reported in ZnO nanostructures prepared by various methods [3]–[5], however, in our knowledge, no reports of random lasing created by Chemical bath deposition techniques have been reported up to date. In this paper, we report on the size dependence of random lasing threshold from ZnO nanostructures grown on glasss substrates using a simple and environmental friendly chemical bath deposition (CBD) technique at an optimal temperature of 96oC and stayed in the solution for 4 hours [6]. To improve its optical properties, these ZnO nanostructures were annealed at 600 oC with oxygen (O2) ambient atmosphere. Micro-photoluminescence (μ-PL) was utilised to analyse the optical properties of the ZnO nanostructures under the excitation of a 266-nm Nd: YAG pulsed laser. The lasing intensities of three different rod diameters of the ZnO nanostructures, 58 nm, 63 nm and 100 nm respectively, were investigated with different excitation densities to observe the threshold of random lasing in these structures. At threshold, only the nominal photoluminescence peak was observed centered around 380 nm. Above the threshold condition, a sharp peak start to appear and in one case, after a particular value of excitation power more than one mode appeared. These peaks, attributed to random lasing, increased non linearly with excitation power. The width of the spectral line of the lasing peak was less between 0.20 nm and 0.26 nm, depending on the size of the nanostructure, giving a high Q-factor of about 1,900 and 1480, calculated using Q = λ / δλ, where λ is the peak wavelength, which is higher than some other ZnO structures [7]. The lowest threshold was observed at 0.15 mW excitation power for ZnO nanorods with average diameters of 58 nm with a spectral line width of 0.20 nm providing a Q-factor of about 1900. Moreover, possible steady state region was observed after 0.4 mW of excitation power. Overall, nanorods having average diameters of 58 nm showed the lowest threshold compared to nanorods with diameters of 63 nm and 100 nm whereas random lasing was also observed in 50 nm nanrods however it was not strong enough to observe threshold behaviour. Hence we conclude that size does play a role in achieving steady state and random lasing as well as in lowering the threshold condition for ZnO nanostructures grown using low cost techniques. This unique optical characteristic may facilitate the development of high-efficiency random lasers grown using low cost methods for future devices.
Keywords: Random lasing, ZnO nanostructures, chemical bath deposition, random lasing threshold
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