Excitonic Features in the Optical Response of Layered Gallium Sulphide

Lately, interest in phase-change materials has been renewed in order to design a new generation of active optical reconfigurable devices in combination with plasmonic technologies to achieve low consumption and ultrafast characteristics for a wide range of applications spanning from optical switches, photonic memories, logical gates, etc. Within the possible candidate materials, gallium sulphide exhibits desirable properties as a marked change in the optical properties between crystalline and amorphous phases, low losses at visible frequencies, stability in environmental conditions, to name a few. Therefore, an accurate description of its optical response is desirable to predict the behavior subject to external excitations. In this contribution we present the modelling of the dielectric function of crystalline GaS from ab-initio calculations, including excitonic effects to achieve quantitative agreement with experimental results.