Extraordinary transmission in the ultraviolet band in a (Al_<i>x</i>Ga_1-<i>x</i>)₂O₃/Al nanopore array

Abstract

The Finite Difference Time Domain method was used to compute the transmission of periodic triangular-lattice Al nanopore arrays on (Al_<i>x</i>Ga_1-<i>x</i>)₂O₃ thin film substrates. The impact of Al component <i>x</i> in(Al_<i>x</i>Ga_1-<i>x</i>)₂O₃ substrate, as well as the thickness, aperture and period of Al nanopore array on its optical transmission behavior was studied systematically.<br>The numerical results indicate there are two strong transmission peaks at 263 nm and 358 nm when <i>x</i>=0. As x increases, the transmission peak at 263 nm exhibits a slight blue-shift with an initial increase followed by a decrease in intensity. Meanwhile, the transmission peak at 358 nm demonstrates a noticeable blue-shift and its intensity strengthens continuously. The change of Al component <i>x</i> has a significant effect on the peak position of the transmission peak in the longer ultraviolet band and the peak transmission in the shorter ultraviolet band. If the periodic structure of the nanopore array keeps unchangeable, the two prominent transmission peaks appear near 244 nm and 347 nm respectively as the air column apertures enlarge. Remarkably, these dual peaks initially undergo a red-shift, and subsequently a blue-shift, all while the transmission rises steadily and the reflectivity diminishes. The change in aperture size can significantly affect the peak transmission, and by controlling the aperture size appropriately, the transmission intensity can be significantly enhanced. With the expansion of the period, the two strong transmission peaks are located at 249 nm and 336 nm respectively, and the two transmission peaks show obvious red-shift. The former transmission peak is redshifted to 304 nm, and the latter one is redshifted to 417 nm. Moreover, the transmission at these peaks continues to decrease. The change in period can significantly affect the central wavelength of the transmission peak, and the periodicity of the array plays a dominant role in modulating the peak position over a large wavelength range. As Al thickness increases, a blue-shift of the transmission peak at 380 nm occurs, and the transmission decreases continuously. The change in thickness significantly affects the transmission intensity of the transmission peak in the longer ultraviolet band and the visible light region, but it is not as pronounced as the effect of aperture size on transmission intensity.<br>Through reasonable design and optimization of structural parameters of Al nanopore array/(Al_<i>x</i>Ga_1-<i>x</i>)₂O₃, the peak position of transmission peak can be effectively regulated and the extraordinary transmission in ultraviolet band can be achieved.