Condensed matter physics, Optics

Previous and Current Research

Future Projects and Goals

The main scientific activity is aimed at creating a diagnostic system of experimental and theoretical studies of semiconductor materials for their use as detectors of ionizing radiation. In particular, the processes of generation and drift of free charge carriers in semiconductors after the absorption of X-ray quanta are studied in detail. Particular attention is paid to the theoretical study of the kinetics of X-ray conductivity and photoconductivity in broadband semiconductors. The main disadvantages of ZnSe crystals for their use as spectrometric detectors of ionizing radiation are studied in parallel.

The conductivity and luminescence characteristics of a series of high-resistance ZnSe single crystals were comprehensively studied in the works of research group's members. First of all, studies of dark conductivity confirmed that the electrical contacts used are ohmic and found that the conductivity is due to free electrons. The obtained luminescence spectra of these crystals at different temperatures and different intensities of X-ray and UV excitation showed that the shape of the spectra does not depend on the nature of the excitation. Conducted volt-ampere studies of X-ray and photoconductivity at different temperatures and different excitation intensities showed their nonlinear nature. It is established that the temperature dependences of the X-ray and photoconductivity current are caused, first of all, by the temperature dependence of the mobility of free electrons. The obtained lux-ampere and lux-luminescent characteristics of ZnSe crystals at different temperatures under X-ray and UV excitation are almost linear. Experimental studies of conduction current relaxation, phosphorescence, thermostimulated conductivity and luminescence show the presence of a whole range of traps. The main parameters of these traps are set. All the obtained experimental dependences are consistent with the kinetic theory. A large amount of necessary data will be provided by studies of IR-absorption and Raman and luminescence excitation spectra. Further study of the physical processes of X-ray conductivity and X-ray luminescence of ZnSe crystals will have a logical continuation in the formulation of recommendations for their practical use as semiconductor detectors of ionizing radiation.

The complex installation for carrying out experimental researches is used, which is in laboratory 338 of Experimental physics department, Faculty of Physics of Taras Shevchenko National University of Kyiv. The block diagram of the experimental setup is shown in Fig. 1.

Fig.1 The block diagram of the experimental setup. 1 – sources of excitation; 2 – cryostat; 3 – registration system blocks.

Design features of such a complex installation for spectral-luminescent and opto-electrical studies of optical materials (laser elements, scintillators, phosphors, semiconductors, etc.) and their radiation resistance make it possible to use a large number of experimental techniques, the main of which are:

• photo- and X-ray luminescence spectra (PL, XRL) in the region of 200-1200 nm;

• photo- and X-ray conductivity (PC, XRC) (voltage up to 1000 V, current of 1 pA);

• luminescence excitation spectra and photoconductivity;

• temperature dependences of PL, XRL, PC, XRC;

• dose dependences of PL, XRL, PC, XRC;

• thermally stimulated luminescence and conductivity;

• optically stimulated luminescence and its kinetics;

• optical absorption and reflection spectra (200-1200 nm);

• additional optical absorption by UV or X-ray irradiation;

• temperature and optical destruction of color centers;

• temperature and volt-ampere dependences of dark conductivity, PC, XRC;

• lux-ampere dependences of PL, XRL;

• kinetics of phosphorescence and relaxation of conduction current.

One part of these methods is implemented according to the scheme shown in Fig. 1, and for the second part of the experimental methods it is necessary to swap optical excitation sources with a quartz capacitor with PEM. The installation is an open system, i.e. there is an opportunity to introduce new research methods, such as XRL excitation spectra. Practice of work on this installation shows that in several hours of work it is possible to receive up to 20 experimental dependences.

Group leader: Volodymyr Degoda, Dr. Sci. (Phys.&Math.), Prof.

h-index: 14, https://www.scopus.com/authid/detail.uri?authorId=54915236500

The team:

Dr.Sci Doroshenko I., h-index: 12;

https://www.scopus.com/authid/detail.uri?authorId=6701318684 ;

PhD Podust G., h-index: 3;

https://www.scopus.com/authid/detail.uri?authorId=55371683100 ;

PhD Pavlova N., h-index: 4;

https://www.scopus.com/authid/detail.uri?authorId=56406180100 ;

Kogut Ya., h-index: 6;

https://www.scopus.com/authid/detail.uri?authorId=56117538400 ;

In collaboration with:

PhD Losytskyy M., h-index: 21;

https://www.scopus.com/authid/detail.uri?authorId=6603498681 ;

Dr.Sci. Danevich F., h-index: 42;

https://www.scopus.com/authid/detail.uri?authorId=6701545407 ;

Methodological and Technical Expertise

• spectroscopy of semiconductor structures;
• semiconductor detectors of ionizing radiation;
• kinetics study of X-ray luminescence and conductivity of broadband semiconductors and dielectrics;
• kinetic theory of X-ray luminescence and conductivity of crystal phosphors;
• study of photoelectric properties of semiconductor materials;

Member of two specialized scientific councils D26.001.08 та D26.001.23 in Taras Shevchenko National University of Kyiv (Faculty of Physics).

Selected Publications

1. V.Ya. Degoda, M. Alizadeh, Ya.P. Kogut, N.Yu. Pavlova, S.V. Sulima,  The influence of UV excitation intensity on photoconductivity and luminescence in ZnSe crystals. Journal of Luminescence. 2019. V. 205. No 1. P.540-547

2. V.Ya. Degoda, M. Alizadeh, N.O. Kovalenko, and N.Yu. Pavlova, The Dependencies of X-Ray Conductivity and X-Ray Luminescence of ZnSe Crystals on the Excitation Intensity. Advances in Condensed Matter Physics. 2018. Volume 2018, Article ID 1515978, 8 pages. https://doi.org/10.1155/2018/1515978

3. V.Ya. Degoda, M. Alizadeh, N.V. Martynyuk, N.Yu. Pavlova, Dose Dependences of the Conductivity and Luminescence in ZnSe Single Crystals. ACTA PHYSICA POLONICA A. 2018. V. 133. No. 4. P.984-989. DOI: 10.12693/APhysPolA.133.984.

4. V.Ya. Degoda, M. Alizadeh, N.O. Kovalenko, and N.Yu. Pavlova  V-I characteristics of X-ray conductivity and UV photoconductivity of ZnSe crystals. J. of Appl. Phys. 2018. V. 123. 075702  doi.org: 10.1063/1.5012597

5. V.Ya. Degoda, Ya.P. Kogut, I.M. Moroz, F.A. Danevich, S.G. Nasonov, E.P. Makarov, V.N. Shlegel,  Temperature dependence of luminescence intensity in ZnMoO4 crystals. Materials Research Bulletin. 2017. V. 89. P.139-149 (doi: 10.1016/j.materresbull.2017.01.010)

6. Degoda V.Ya., Pivovarenko V.G., Moroz I.M., Shilov D.Yu.  The concentration dependence for X-ray excited luminescence in liquid phosphors. J. Luminescence. 2015. V. 165. P. 174-178.

7. Degoda V. Ya., Pavlova N. Yu., Podust G.P., Sofiienko A.O.  Spectral structure of the X-ray stimulated phosphorescence of monocrystalline ZnSe. Physica B: Condensed Matter. 2015. V. 465. P. 1-6.

8. M.S. Brodin, V.Ya. Degoda, B.V. Kozhushko, A.O. Sofiienko, V.T. Vesna  Monocrystalline ZnSe as an ionising radiation detector operated over a wide temperature range. Radiation Measurements. 2014. V. 65. P.36-44.

9. Degoda V.Ya., Sofiienko A.O. Effect of traps on current impulse from X-ray induced conductivity in wide-gap semiconductors. Physica B. 2013. V. 426. P.24-30.

10. Sofiienko A.O., Degoda V.Ya. X-ray induced conductivity of ZnSe sensors at high temperatures. Radiation Measurements. 2012. V. 47. № 1. P.27-29. 

https://orcid.org/0000-0001-7984-8589

https://www.scopus.com/authid/detail.uri?authorId=54915236500

Contacts

degoda@univ.kiev.ua