Thin layer interference effects on optical properties of layered BiI₃

When precise measurement of optical properties in very thin systems, such as 2D materials, is required, thin layer interference effects play a crucial role. This is particularly important when a thickness-dependent characterization is needed. Contrary to intuition, these kind of effects can take place even when the investigated thicknesses are well below the probing wavelength scale.

In our work we have studied the layer-dependent optical properties of the archetypal 2D semiconductor BiI₃, with thicknesses varying from the monolayer to the mesoscale. This material is of high interest for possible applications in optoelectronics, photovoltaics and X-Ray detection systems.

This study, based on transmission and photoluminescence measurements, allowed us to estimate how a strongly bound exciton in the material causes a giant stokes shift. A parallel thin layer interference analysis allowed us to disentangle the intrinsic material properties from simple optical effects in the measured phenomena.