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Study of photo- and thermally-induced changes in Ge-As-S thin films by spectroscopic ellipsometry♣

V. PAMUKCHIEVA1,* , A. SZEKERES1, D. ARSOVA1

Affiliation

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

Abstract

The effect of illumination and post-illumination annealing on the optical properties and thicknesses of thin (~ 150 nm) films of Ge 30.8As 5.7S 63.5 and Ge 32 As 5S 63 glasses belonging to Ge2S3-AsS 3 system was studied by means of spectroscopic ellipsometry in the spectral range 300 - 820 nm. The amorphous films were prepared by thermal evaporation onto glass substrates. The ellipsometric measurements were performed after each technological step, i.e. on the freshly deposited samples and after their UV-illumination and subsequent thermal annealing at a temperature of 350 o C. Illumination of the films caused a considerably increase in the film thickness (12-13 %) and a large change in the optical constants. An effect of photo-bleaching was observed; the increase in the optical gap energy Eg was as large as ΔE g = 240 meV and 400 meV for the Ge 30.8As5.7S 63.5 and Ge32As 5S 63 films, respectively. Annealing lead to a further increase of the E g value, by ~100 meV, and to a contraction of the film volume. The observed effects were attributed to photo-induced structural change in the Ge-As-S amorphous network..

Keywords

Chalcogenide thin films, Spectroscopic ellipsometry, Photoindused changes, Optical properties.

Submitted at: Nov. 5, 2008
Accepted at: Sept. 9, 2009

Citation

V. PAMUKCHIEVA, A. SZEKERES, D. ARSOVA, Study of photo- and thermally-induced changes in Ge-As-S thin films by spectroscopic ellipsometry♣, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 9, pp. 1249-1252 (2009)