Layer-dependent optical and dielectric properties of CdSe semiconductor colloidal quantum wells characterized by spectroscopic ellipsometry

Abstract Semiconductor colloidal quantum wells (CQWs) with atomic-precision layer thickness are rapidly gaining attention for next-generation optoelectronic applications due to their tunable optical and electronic properties. In this study, we investigate the dielectric and optical characteristics of CdSe CQWs with monolayer numbers ranging from 2 to 7, synthesized via thermal injection and atomic layer (c-ALD) deposition techniques. Through a combination of spectroscopic ellipsometry (SE) and first-principles calculations, we demonstrate the significant tunability of the bandgap, refractive index, and extinction coefficient, driven by quantum confinement effects. Our results show a decrease in bandgap from 3.1 to 2.0 eV as the layer thickness increases. Furthermore, by employing a detailed analysis of the absorption spectra, accounting for exciton localization and asymmetric broadening, we precisely capture the relationship between monolayer number and exciton binding energy. These findings offer crucial insights for optimizing CdSe CQWs in optoelectronic device design by leveraging their layer-dependent properties.