Comparison of nano holes and nano pillars moth eye structures for mid-wave infrared

Abstract

Subwavelength moth eye structures are the nanostructures arranged uniformly whose feature size is less than the incident optical wavelength. These structures are promising to reduce the reflection of any material by creating a refractive index gradient profile at the interface surface. Mid-wave infrared (MWIR) is an important wavelength to investigate the moth eye structures for various applications like photovoltaic, solar cells and display technologies. In this paper, we fabricated two different moth eye structures Nano pillars and Nano holes using the simple and robust lithography technique. Using silicon dioxide as a hard mask, structures are transferred onto gallium arsenide substrate using different etching conditions. We compared the transmission of nanoholes and nanopillars structures and find out that nanoholes structures shows better transmittance in MWIR. We also obtained theoretical transmission data using rigorous coupled wave analysis (RCWA) which agrees with our experimental data. Moreover, Nano holes structures has an advantage over nanopillars structure as the former are resistant against contamination which therefore will not lead to decrease in transmission performance. The characterization results of the structures are obtained from SEM which shows the morphologies of the structures. Our approach is reproducible and can be easily applied to any optical devices which require antireflective property.