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SIZE EFFECTS AND LATTICE DISORDER IN GeS2/CdSe NANOSTRUCTURES

D. Nesheva1,* , Z. Levi1, Z. Aneva1

Affiliation

  1. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria

Abstract

This article summarizes results on GeS2/CdSe superlattices (SLs) and composite films (CFs) which are prepared by consecutive thermal evaporation of CdSe and GeS2 in vacuum. An overall blue shift of the absorption spectra of SLs is observed with decreasing CdSe layer thickness related to a size-induced increase of the optical band gap of CdSe due to one dimensional carrier confinement in the continuous nanocrystalline CdSe layers. This assumption is proven by the results of photoreflectance measurements. A number of features are observed in the absorption spectra of CFs. They are discussed in terms of three dimensional carrier confinement and considered as a manifestation of excited electron states in CdSe nanocrystals. Resonant Raman effects are observed in the CFs and related to resonant absorption in the excited electron states. Electronic defects in CdSe nanocrystals of SLs and CFs are investigated by transient and spectral photocurrent investigations. Two wide bands of localized states centred at 0.55 eV and 0.50 eV below the conduction band edge are seen and identified with defects in the nanocrystal bulk and defects at the GeS2/CdSe interface, respectively. The effect of CdSe nanocrystal incorporation on the level of disorder in the GeS2 matrix of CFs is also investigated. It is observed that the presence of CdSe nanocrystals with average diameter >2.5 nm in the GeS2 matrix impedes the photoinduced structural changes in GeS2..

Keywords

CdSe thin films, Photoconductivity, Thermally stimulated currents, Defect states.

Submitted at: May 11, 2005
Accepted at: July 21, 2005

Citation

D. Nesheva, Z. Levi, Z. Aneva, SIZE EFFECTS AND LATTICE DISORDER IN GeS2/CdSe NANOSTRUCTURES, Journal of Optoelectronics and Advanced Materials Vol. 7, Iss. 4, pp. 1837-1846 (2005)