High transparent mid-infrared silicon “window” decorated with amorphous photonic structures fabricated by facile phase separation

High transparency in the infrared (IR) region is desirable for most common IR materials and devices, due to their high interfacial reflectance, resulting from the high refractive indices of constituent substances. Herein, a new strategy, with using phase-separated polystyrene (PS)/polymethylmethacrylate (PMMA) blends as masks, is proposed to fabricate subwavelength structures for Si with significantly enhanced mid-IR transmission. Maximum transmittance approaching to 70% and 90% are achieved with single and double-side structured Si respectively. The fabricated subwavelength structures are short-range ordered amorphous photonic structures (APSs). By using different spin-coating speeds and molar ratios of PS to PMMA and by adjusting the etching duration time, tunable enhanced transmission are also obtained. The good performance of high transmission is confirmed by mid-IR thermal imaging experiments. Furthermore, the enhanced transmission is effective over a wide range of incident angles up to 50° and well maintained at high temperatures up to 600 °C.