Total absorption of visible light in ultra-thin weakly-absorbing semiconductor gratings

TL;DR

This paper demonstrates that ultra-thin, weakly-absorbing semiconductor gratings can achieve near-perfect visible light absorption, enabling efficient optoelectronic devices without exotic materials.

Contribution

It introduces a method to realize total light absorption in ultra-thin, conventional semiconductor gratings, challenging the need for exotic materials or thick structures.

Findings

Achieved 99.3% absorption in a 41 nm antimony sulphide grating

Theoretical and experimental absorption are in excellent agreement

Absorption is primarily within the semiconductor, with minimal loss in the mirror

Abstract

The perfect absorption of light in subwavelength thickness layers generally relies on exotic materials, metamaterials or thick metallic gratings. Here we demonstrate that total light absorption can be achieved in ultra-thin gratings composed of conventional materials, including relatively weakly-absorbing semiconductors, which are compatible with optoelectronic applications such as photodetectors and optical modulators. We fabricate a 41 nm thick antimony sulphide grating structure that has a measured absorptance of A = 99.3% at a visible wavelength of 591 nm, in excellent agreement with theory. We infer that the absorption within the grating is A = 98.7%, with only A = 0.6% within the silver mirror. A planar reference sample absorbs A = 7.7% at this wavelength.