Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 28 WEDNESDAY AFTERNOON
JS1-WeA-P.8 ON THE INFLUENCE OF TE EXCESS ON THE OPTICAL PROP-
ERTIES OF VACUUM EVAPORATED ZNTE THIN FILMS. P. Prepeliţă, M.Rusu, C.Baban,
G.I.Rusu. Faculty of Physics “Al. I. Cuza” University, B-dul Carol I, No.11, Iasi, Romania. (e-mail:
prepelita@stoner.phys.uaic.ro)
ZnTe thin films are intensively studied due to their interesting properties such as high transmission
coefficient, large energy bandgap, low electrical resistivity, etc. An important factor that influences
the properties of these films is the deviation from their stoichiometric composition. In present paper,
the influence of tellurium excess on the optical properties of evaporated ZnTe thin films is investigated.
The studied films (d = 0.700 µm - 1.300 µm) were deposited onto unheated glass substrates by
evaporation under vacuum of ZnTe powder at source temperature ranged between 900 K and 1200
K. The structural analysis of the films was performed by XRD and AFM techniques. The optical parameters
(refractive index and absorption coefficient) both for as deposited and heat treated samples
were determined from transmission spectra in the spectral range 340 nm - 1400 nm.
It was found that the studied films present a polycrystalline zinc blende structure with preferential
orientation of (111) planes parallel to the substrate. An excess of tellurium atoms which aggregate in
crystallite form during film annealing was observed. This Te excess determines a significant increase
of the absorption coefficient near the fundamental absorption edge and of refractive index in the infrared
domain. Depending on Te content, the optical bandgap energy, E g , calculated from the absorption
spectra, ranged between 1.9 eV and 2.4 eV.
The results are discussed in correlation with film structure and the impurity levels introduced by the
Te excess.
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