Specific features of the luminescence and conductivity of zinc selenide on exposure to X-ray and optical excitation

The set of experimental data on the X-ray-excited luminescence and X-ray induced conductivity of ZnSe are compared to the data on the photoluminescence and photoconductivity. It is experimentally established that the current-voltage characteristics and the kinetics of phosphorescence and current relaxation depend on the type of excitation. It is found that the external electric field influences the intensity and shape of bands in the luminescence spectra. It is shown that the character of excitation defines the kinetics of recombination, charge carrier trapping, and conductivity in wide-gap semiconductors.Comment: 7 pages, 7 figures, published in Fizika i Tekhnika Poluprovodnikov, 2010, Vol. 44, No. 5, pp. 594-59

Purification of molybdenum oxide, growth and characterization of medium size zinc molybdate crystals for the LUMINEU program

The LUMINEU program aims at performing a pilot experiment on neutrinoless double beta decay of 100Mo using radiopure ZnMoO4 crystals operated as scintillating bolometers. Growth of high quality radiopure crystals is a complex task, since there are no commercially available molybdenum compounds with the required levels of purity and radioactive contamination. This paper discusses approaches to purify molybdenum and synthesize compound for high quality radiopure ZnMoO4 crystal growth. A combination of a double sublimation (with addition of zinc molybdate) with subsequent recrystallization in aqueous solutions (using zinc molybdate as a collector) was used. Zinc molybdate crystals up to 1.5 kg were grown by the low-thermal-gradient Czochralski technique, their optical, luminescent, diamagnetic, thermal and bolometric properties were tested.Comment: Contribution to Proc. of Int. Workshop on Radiopure Scintillators RPSCINT 2013, 17-20 September 2013, Kyiv, Ukraine; to be published in EPJ Web of Conferences; expected to be online in January 2014; 6 pages, 6 figures, and 3 table

Kinetics of Charge Transport in Wide-Band Semiconductors at the Detection of X-Ray Radiation

As a result of absorption of X-ray quantum in a semiconductor, the generation of electron-hole pairs takes place in a small volume (diameter < 0.5 μm). Their surplus energy is lost due to the scattering on phonons of the crystal lattice. Spatial distribution of the charge carriers makes the form of current pulse on electrodes of the crystal complicated when an external electric field is applied. We present a logical chart of construction of basic kinetic model of X-ray conductivity (XRC) in semiconductors that uses the successive in time calculation of the spatial distribution of free charge carriers and the diffusive-drift model of motion of free carriers in a solid. The basic form of current pulse in an external circle was obtained in the analytical kind for the case of an ideal semiconductor, e.g. that does not contain deep traps and recombination centers, as well as for the case of a crystal with dominant shallow or deep traps of electrons and holes

Kinetics of Charge Transport in Wide-Band Semiconductors at the Detection of X-Ray Radiation

As a result of absorption of X-ray quantum in a semiconductor, the generation of electron-hole pairs takes place in a small volume (diameter < 0.5 μm). Their surplus energy is lost due to the scattering on phonons of the crystal lattice. Spatial distribution of the charge carriers makes the form of current pulse on electrodes of the crystal complicated when an external electric field is applied. We present a logical chart of construction of basic kinetic model of X-ray conductivity (XRC) in semiconductors that uses the successive in time calculation of the spatial distribution of free charge carriers and the diffusive-drift model of motion of free carriers in a solid. The basic form of current pulse in an external circle was obtained in the analytical kind for the case of an ideal semiconductor, e.g. that does not contain deep traps and recombination centers, as well as for the case of a crystal with dominant shallow or deep traps of electrons and holes

Dose Dependences of the Conductivity and Luminescence in ZnSe Single Crystals

The studies of time-resolved dose dependences of conductivity and luminescence in ZnSe crystals at various temperatures (8, 85, 295, and 430 K) under X-ray and UV-excitation have revealed that dose dependences under X-ray excitation build up much more slowly and are more informative in comparison with UV-excitation. It is due to high penetrating depth of X-ray radiation and respective involvement of a large sample volume in the kinetic processes. Also, due to the local inhomogeneity of the excitation in the absorption of X-quantum, a significant share of the generated electron-hole pairs recombine in this local area creating a scintillation pulse, and not participating in the conductivity. The delay in the onset of the X-ray conductivity buildup at 8 K for several seconds is due to the high efficiency of the localization of free carriers in the traps, all of which become deep at this temperature. The different buildups of various bands of luminescence of irradiation time can be explained by not only different concentration of luminescence centers but also by their localization in various sections of free charge carriers. Dose dependences of the luminescence and conductivity also show that the scintillation pulse amplitudes and the current pulse amplitudes of the X-ray conductivity are not constant during irradiation of the ZnSe crystals