Fabrication of inverted zinc oxide photonic crystal using sol–gel solution by spin coating method
© Huang et al.; licensee Springer. 2013
Received: 4 March 2013
Accepted: 20 April 2013
Published: 2 July 2013
Inverted zinc oxide photonic crystal structures were fabricated from polystyrene sphere (PSS) template using the sol–gel solution of ZnO by spin-coating method. It is easily able to control and fabricate the photonic crystal structures using the self-organized PSS with a size of 193 nm. The inverted ZnO photonic crystal structures observed show the (111) tendency of the hexagonal compact arrangement formation. The resulting structures possess the photonic band gaps in the near-ultraviolet range and exhibit an enhanced photoluminescence spectrum. The technology can effectively increase the light output intensity or efficiency for the applications of optoelectronic devices.
Since photonic crystals (PhCs) were first proposed in 1987 by Yablonovitch  and John , they have been studied with great interest as a means of localizing light and modifying the emission properties of embedded light sources . Material infiltration of three-dimensional (3D) polystyrene sphere (PSS) PhC has been a versatile method to fabricate the so-called inverted structure, which has long-range order, high filling fraction, and refractive index contrast required to exhibit a photonic band gap. Infiltration has been recently achieved by various methods, including chemical bath deposition , electrodeposition , and low-pressure chemical vapor deposition . To achieve both high filling fractions and good luminescence properties of this material has been proven difficult . In spite of the few studies regarding the sol–gel method, this method has some advantages, such as the easy control of chemical components and fabrication of thin film at low cost to investigate the structural and optical properties of ZnO thin films. Several groups have, therefore, studied the emission properties of lasing dyes or quantum dots infiltrated into inverted opal backbones . Teh et al. reported that the optical gain of the 3D ZnO inverse opal fabricated by electrodeposition is further enhanced due to the localized defect modes within the primary photonic pseudogap. Teh et al. reported the room-temperature ultraviolet lasing and the mechanisms of lasing modes in 3D ZnO inverse opals fabricated via colloidal templating with electrochemical infiltration. They further investigated the mechanisms of lasing modes and deduced that periodic structures would facilitate strain-induced change in lasing energy and provide modulation in refractive index for enhanced light confinement as well as optical feedback. They concluded that the periodic photonic structure plays a role, i.e., the modulation in refractive index would enhance the light confinement as well as the optical feedback . The inverted ZnO PhC possesses a wide electronic band gap (3.2 eV at room temperature) and high exciton binding energy (60 meV), which makes it an efficient short-wavelength light source in the near ultra-violet (NUV) spectrum. Its refractive index (2.26) is too low to produce a full (i.e., omnidirectional) photonic band gap but sufficient for the formation of directional pseudogaps. In this article, we report the fabrication of inverted ZnO PhC using sol–gel solution by spin coating method and demonstrate the morphology, reflection spectra, and luminescence in the NUV region for the examination of the process on inverted ZnO PhCs.
Summary and conclusions
We have successfully fabricated the inverted ZnO PhC structure using the sol–gel solution of ZnO by spin coating method. Sol–gel is capable of producing high filling fraction inverted opal materials with very good crystalline quality. The results of the inverted ZnO structure exhibit clear strong NUV photoluminescence at the wavelength of 378 nm, which makes them interesting candidates for studying the characteristics of modified spontaneous and stimulated emission in active ZnO PhCs. The combination of aqueous chemical growth and nanosphere lithography is expected to provide a facile, large-scale, and low-cost fabrication method at low temperatures, which shall be of significant value for practical applications of the grown PhCs.
The financial support from National Science Council (101-2218-E-007-007 and 100-2221-E-007-084-MY3) is deeply appreciated.
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