Grain size dependent optical properties of CdI2 films

P. Tyagi; A. G. Vedeshwar

doi:10.1051/epjap:2002043

All issues

Volume 19 / No 1 (July 2002)

Eur. Phys. J. AP, 19 1 (2002) 3-13

Abstract

Issue		Eur. Phys. J. AP Volume 19, Number 1, July 2002


Page(s)		3 - 13
Section		Surfaces, Interfaces and Films
DOI		https://doi.org/10.1051/epjap:2002043
Published online		28 June 2002

Eur. Phys. J. AP 19, 3-13 (2002)
https://doi.org/10.1051/epjap:2002043

Grain size dependent optical properties of CdI₂ films

P. Tyagi and A. G. Vedeshwar

Thin Film Lab, Department of Physics & Astrophysics, University of Delhi, Delhi – 110 007, India

Corresponding author: agni@physics.du.ac.in

Received: 12 April 2001
Revised: 25 January 2002
Accepted: 4 April 2002
Published online: 28 June 2002

Abstract

The optical properties (refractive index and optical energy gap) were studied as a function of film thickness, substrate temperature and heat-treatment temperature for structurally, compositionally and morphologically well characterized CdI₂ films grown by thermal evaporation. The variation of residual stress in the film (determined by X-ray diffraction), grain size (D), refractive index (n) and optical energy gap (E_g) was observed to be different in the above three cases. Combining the results of all three experiments, the grain size dependence of n and E_g was derived. Variation of n with grain size may be attributed to the changing packing density of crystallites with grain size and its distribution consistent with SEM results. E_g was found to decrease with D non-linearly and the data fits well with the equation of the type either $E_{\rm g}(D)=3.61-0.023D-0.0034D^2$ or $E_{\rm g}(D)=3.59-\frac{0.075 D^2}{(2+D)}\cdot$ The variation of E_g with D could be attributed as due to the defect densities in the film.

PACS: 68.55.Jk – Structure and morphology; thickness; crystalline orientation and texture / 78.20.Ci – Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity) / 81.15.Ef – Vacuum deposition / 78.66.Nk – Insulators

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