Size-dependent absorption and defect states in CdSe nanocrystals in various multilayer structures

Area of Science:

• Materials Science
• Nanotechnology
• Solid State Physics

Background:

• Germanium disulfide (GeS2) and cadmium selenide (CdSe) are semiconductors with potential applications in optoelectronics.
• Superlattices and composite films offer tunable electronic and optical properties through controlled nanostructure fabrication.

Purpose of the Study:

• To investigate the optical absorption and carrier confinement effects in GeS2-CdSe superlattices and composite films.
• To understand the influence of varying CdSe layer thickness and nanocrystal size on material properties.

Main Methods:

• Preparation of GeS2-CdSe superlattices and composite films via consecutive thermal evaporation.
• Optical absorption studies using spectral photocurrent and constant photocurrent methods.
• Transient photoconductivity measurements to analyze charge transport dynamics.

Main Results:

• A blueshift in optical absorption was observed with decreasing CdSe layer thickness in superlattices, attributed to 1D quantum confinement.
• Absorption spectra of composite films showed features related to 3D confinement in CdSe nanocrystals and Urbach tail states.
• Transient photoconductivity in SiOx-CdSe superlattices indicated multi-trapping transport via deep defects.

Conclusions:

• Quantum confinement effects significantly influence the optical band gap of CdSe in GeS2-CdSe nanostructures.
• The observed phenomena are consistent with carrier confinement in both 1D and 3D regimes, depending on the material architecture.
• Disorder and deep defects play a role in the electronic transport properties of these semiconductor heterostructures.