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Structural characterization and photoluminescence of ZnSe nanolayers♣

D. NESHEVA1,* , M. J. ŠĆEPANOVIĆ2, Z. LEVI3, S. AŠKRABIĆ2, Z. ANEVA1, A. PETROVA4, Z. V. POPOVIC2

Affiliation

  1. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria
  2. Institute of Physics (IF), Pregrevica 118, Belgrade 11080, Serbia and Montenegro
  3. Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee Blvd., 1784 Sofia, Bulgaria.
  4. Space Research Institute, Bulgarian Academy of Sciences, P.O. Box 799, 1000 Sofia, Bulgaria

Abstract

Single layers of ZnSe (30, 40, 50, 70, 100 nm and 1 μm thick) are deposited at room substrate temperature by thermal evaporation of ZnSe powder in vacuum. The film surface morphology and structure are investigated by Atomic Force Microscopy (AFM). The as-deposited films are smooth and homogeneous while the relaxed ones show pits on the surface and a root mean square roughness of 2 - 4 nm. It is assumed that as-deposited films are highly strained and the strain relaxation with time creates pits and increases the surface roughness. Optical transmission measurements on relaxed films (≤ 100 nm thick) show an energy dependence of the absorption coefficient typical of amorphous materials, but the AFM data indicate the presence of nanocrystals (apparent grain size 25 - 30 nm). Therefore, it is assumed that the layers contain two phases, amorphous and crystalline, and the portion of the crystalline phase decreases with decreasing thickness. Photoluminescence (PL) measurements carried out at various temperatures in the range 20 – 300 K reveal two bands in the spectra of all films, centred at ~ 500 and ~ 550 nm. The bands are related to radiative recombination in the crystal phase, via two kinds of deep acceptors which are not discrete but have certain energy distributions in the forbidden gap..

Keywords

Thin films, ZnSe, Thermal vacuum evaporation, Atomic force microscopy, Photoluminescence.

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

Citation

D. NESHEVA, M. J. ŠĆEPANOVIĆ, Z. LEVI, S. AŠKRABIĆ, Z. ANEVA, A. PETROVA, Z. V. POPOVIC, Structural characterization and photoluminescence of ZnSe nanolayers♣, Journal of Optoelectronics and Advanced Materials Vol. 11, Iss. 9, pp. 1351-1354 (2009)