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Preparation of micro - and nanocrystalline CdSe and CdS thin films suitable for sensor applications

D. NESHEVA1,* , Z. ANEVA1, S. REYNOLDS2,3, C. MAIN3, A. G. FITZGERALD3

Affiliation

  1. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
  2. Institut für Photovoltaik, Forschungszentrum Jülich GmbH, D-52425 Jülich, Germany
  3. University of Dundee, Division of Electronic Engineering and Physics, Dundee DD1 4HN, UK

Abstract

Thin films of CdS (30-200 nm) and CdSe (10-100 nm) are prepared by physical vapour deposition using one-step (for CdS and CdSe) or step-by-step (for CdSe only) approach. Atomic force microscopy measurements reveal a grain size decrease with decreasing layer thickness. The effect is strongest in the step-by-step CdSe layers. Raman scattering measurements show an anticipated gradual increase of the scattered light from CdS layers with thickness and a non-monotonous change in the CdSe group, the intensity is strongest for the ’50 nm’ ‘step-by-step’ CdSe layer. This observation is ascribed to a size induced increase of the optical band gap of a part of the microcrystals whose estimated size is ~ 8 nm. Room temperature investigations of the effect of exposure to a set of vapours (water, ethanol, ammonia, acetone, iodine) on the dc dark and steady state photoconductivity of CdS layers show a reasonable response of all CdS layers to water vapour. CdSe layers are rather insensitive with the exception of the ’50 nm’ layer, as the ‘step-by-step’ layer shows the best sensitivity to all vapours. The observed good gas-sensitivity of the ‘step-by-step’ CdSe layers is ascribed to a much greater integral interface area between nanocrystals and indicates that ‘step-by-step’ deposition of CdSe layers is quite promising for gas sensor applications..

Keywords

Thin films of CdS and CdSe, Physical vapour deposition, Atomic force microscopy, Dark and photoconductivity, Gas sensitivity.

Submitted at: Oct. 10, 2006
Accepted at: Nov. 2, 2006

Citation

D. NESHEVA, Z. ANEVA, S. REYNOLDS, C. MAIN, A. G. FITZGERALD, Preparation of micro - and nanocrystalline CdSe and CdS thin films suitable for sensor applications, Journal of Optoelectronics and Advanced Materials Vol. 8, Iss. 6, pp. 2120-2125 (2006)