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Photo-ESR and optical studies of Cr photoionization transition in CdZnSe:Cr crystals

Krzysztof Swiatek 2Marek Godlewski 2,3Tanya Surkova 1

1. Russian Academy of Sciences, Ural Division, Institute of Metal Physics, 18 S.Kovalevskaya str., GSP-170, Ekaterinburg 620219, Russian Federation
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. Cardinal Stefan Wyszynski University, College of Science, Warszawa, Poland


Excitation processes of radiative recombination of transition metal ions, which are doped in wide band-gap II-VI semiconductors, are of great interest because of possible application for novel optical devices. Recent studies have shown that the Cr2+ + hν -> Cr1+ + hVB photoionization transitions (hν > 2.2 eV) is an efficient channel for excitation of the Cr2+ intra-ion infra-red emission and laser action in ZnSe:Cr. Since common used semiconductor diode lasers emit light in energy range of 1.9 - 2.0 eV, it is interesting to investigate the same problem in a host system with a bit smaller band gap energy than in case of ZnSe.

In this work we study 2+ -> 1+ and 1+ -> 2+ photoionization transitions of chromium ions in CdxZn(1-x)Se:Cr bulk crystals (0=<x=<0.3) in wide temperature range (2 - 300 K). By monitoring changes of the Cr1+ ESR (electron spin resonance) signal under external illumination we are able to determine energies of Cr2+ -> Cr1++ hVB and Cr1+ -> Cr2++ eCB transitions in different CdxZn(1-x)Se host crystals. At low temperature we observe metastable population of photo-excited Cr1+ centers. Free holes created in the valence band (VB) under the 2+ to 1+ ionization of chromium, are efficiently trapped by shallow acceptor centers. We observe also appropriate photoionization bands in low temperature absorption spectra.
Moreover, obtained by us values of the chromium PT energy in CdxZn(1-x)Se agree well with predictions of the universal-level-model and band offsets in CdZnSe/ZnSe heterostructures.


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Presentation: poster at E-MRS Fall Meeting 2003, Symposium A, by Krzysztof Swiatek
See On-line Journal of E-MRS Fall Meeting 2003

Submitted: 2003-05-26 13:22
Revised:   2009-06-08 12:55