Fabrication and optical behavior of graded-index, moth-eye antireflective structures in CdTe

A simple and scalable method, based on dip-coat colloidal lithography, mask reduction, and plasma-based pattern transfer, is presented to create graded-index, moth eye-inspired antireflective features on II–VI semiconductors. Hexagonal arrays of isolated conical frusta with tunable geometry (top diameter = 200–1300 nm, pitch = 310–2530 nm, and height = 790–7100 nm) were realized by isotropic etching of various size silica colloid masks before pattern transfer into the underlying substrate. Substantial increases in single-side direct and total infrared (IR) transmission across the 4–20 μm range (9%–15% for CdTe thin films and 18% for bulk CdTe) were achieved, in excellent agreement with transfer matrix calculations and finite difference time domain optical simulations. The fabrication method presented can be used to enhance efficiency in multiple IR application areas including photovoltaics, optical system components, detectors, and focal plane array imagers.