However, these techniques are still expensive, time consuming, and sophisticated, which block the penetration of commercial market.
In case of transparent glasses, although the importance of AR structures for improvement of optical efficiency, the cost issues have hindered the use of AR structures in applications such as photovoltaics and optoelectronics. In this letter, we present a simple, fast, and cost-effective method for fabricating AR grassy surfaces composed of tapered SWSs on glass substrates. Reactive ion etch (RIE) process of glasses with gas mixture of CF4 and O2 generates nanoclusters that can be used as an etch mask. Control of etch conditions provides optimal AR performance in the visible wavelength ranges. Methods Design and fabrication According to theoretical analysis,
the subwavelength structures BMS202 (SWSs) with high aspect ratio (i.e., fine period and tall height) and continuous tapered shape from the air to the substrate show the widest bandwidth and almost omnidirectional AR properties [1]. However, fine tuning of geometry increases process complexity and costs. It is essential to find the optimal geometry based on the theoretical calculation to obtain a reasonable AR performance. Figure 1 shows the color map of reflectance of the SWSs on glass substrates as a function of height ASP2215 mouse (0 to 400 nm) and wavelength (300 to 800 nm), calculated by a rigorous coupled-wave analysis method [16]. A model was designed in hexagonal lattices of 100 nm, which is small enough to satisfy zeroth order condition (Λ << λ). The dispersion of glass material (BoroFloat 33, Schott, Louisville, KY, USA) was taken into account in this calculation. The apex diameter was set to 50% of the base diameter. Lck The flat surface (height = 0 nm) of glass substrate shows the reflectance of approximately 4% as expected. This reflectance rapidly goes
down to 1% as the height increases from 0 to 150 nm. This is available only when the index difference is not quite big. For semiconductor materials such as silicon and GaAs, the height should be at least >300 nm to have broadband antireflection characteristics. In this study, the SWSs with height of approximately 150 nm were selected as a target value to maintain a low surface reflection. Figure 1 Contour plot of calculated reflectance of tapered SWSs as a function of height and wavelength. Inset indicates a calculated model. Uniform and high-density grassy surfaces were prepared by plasma etching in an RIE system with gas mixture of CF4 (40 sccm) and O2 (10 sccm), as illustrated in Figure 2. First, borosilicate glass substrates (2 × 2 cm2), which is commonly used as an optic component in various fields, were cleaned with acetone, isopropyl alcohol, and deionized (DI) water and loaded into the LY333531 solubility dmso chamber.