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
N.A. Vlasenko, P.F. Oleksenko, Z.L. Denisova, M.A. Mukhlyo, L.I. Veligura

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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