Semiconductor Physics, Quantum Electronics & Optoelectronics. 2007. V. 10, N 3. P. 087-090.
Thermofield Cr+ →Cr 2+ recharging resulting in anomalous
intensification of Cr2+ emission in ZnS:Cr thin-film
electroluminescent structures
V. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine
41, prospect Nauky, Kyiv 03028, Ukraine
Abstract. For the first time, an anomalous strong increase of the Cr 2+ emission intensity
(I) with increasing the applied voltage (V) has been discovered in ZnS:Cr thin-film
electroluminescent structures (TFELS) instead of the I(V) dependence saturation typical
of TFELS of the MISIM type, where M is an electrode, I is an insulator layer and S is an
EL film. The dependence of I on the transferred charge (Q) is very superlinear, whereas
the luminance of the emission of hot electrons, which takes place simultaneously with the
Cr 2+ emission, increases proportionally to Q as it happens usually in TFELS. The
increase of I and Q is accompanied by rising the sample temperature up to 30 – 50 °C.
However, the emission spectrum that is inherent to the 5 E → 5 T 2 transition in the 3d shell
of a Cr 2+ ion is not changed in this case. The above effects are explained by Cr + → Cr 2+
thermofield recharging, which results in an increase of the number not only of free
electrons, but also of Cr 2+ radiation centers. The most probable mechanism of such a
recharging is the Frenkel-Pool field-stimulated thermal ionization of Cr + ions, whose
ionization energy is 0.65…0.82 eV.
Keywords: electroluminescence, thin films, ZnS:Cr, thermofield ionization, Cr +→ Cr 2+
recharging.
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