Investigation of the electronic and optical properties of bilayer CdS as a gas sensor: first-principles calculations

Abstract

Phonon dispersion curves of pristine CdS bilayer.

II–VI Semiconductor-Based Conductometric Gas Sensors: Is There a Future for These Sensors?

“…Many similarities in the behavior of metal oxides and II–VI compounds are also observed during their interaction with gas and water vapor [ 27 , 28 , 29 ]. It is shown that, as in the case of metal oxides, the interaction of II–VI semiconductors with molecules of toxic gases occurs through physisorption and chemisorption, which cause significant changes in the electronic properties of semiconductors, in particular the total and partial density of states and surface charge, which is a necessary condition to observe gas-sensitive effects in materials intended for conductometric gas sensors.…”

“…For example, the interaction of CdS with SO 2 , H 2 S, and SO is stronger compared to CO and CO 2 . While CO 2 and CO showed strong physical adsorption on the CdS layer, SO 2 , H 2 S, and SO molecules showed chemisorption with higher adsorption energies [ 27 ]. Just as for metal oxides, the surface Fermi level ( E F ) shifts towards the midgap with the adsorption of oxygen for II–VI semiconductors, which results in an upward band bend for n-type semiconductors (ZnS, CdS, and ZnSe) [ 25 , 30 ] and a downward band bend for p-type semiconductors (ZnTe) [ 25 ].…”