Studies of the Thermovoltaic Effect in Semiconductors in the Medium Temperature Range

Introduction. A conversion of thermal energy into electrical energy is an urgent task. The thermovoltaic effect (TVE) found in samarium sulfide (SmS ) makes it possible to solve a higher efficiency problem as compared with classical thermoelectric generators operating on the basis of the Seebeck effect. TVE in SmS, is manifested in an appearance of voltage pulses of 0.05 V in continuous mode when a sample is heated to 470 K. Generation of electromotive force (EMF) is associated with a presence of a concentration gradient of defective Sm ions in sulfur sublattice vacancies, with a change in their valence (Sm²⁺ ® Sm³⁺+e^-) and with electronic Mott transitions. TVE discovered subsequently in ZnO, Ge, Si, and in some complex semiconductors, reached only 0.01 V.

Aim. To increase the magnitude of the generated voltage and the operating temperature at TVE.

Methods and materials. By the method of synthesis from simple substances, raw materials were obtained from which SmS/Sm_1-xLn_xS sandwich-type heterostructures were created, where Ln = Eu, Yb. In addition, samples based on a classical thermoelectric PbTe with different degrees of doping of the layers obtained by pressing at high temperature in a vacuum were investigated. On the unique equipment, excluding temperature gradients in samples, TVE was studied.

Results. It was shown that an increase in the EMF value and in the operating temperature had been achieved due to the penetration of donor levels by doping. In doped samples on the basis of SmS, a generation of EMF up to 0.15 V was observed in continuous mode at T = 700 K. TVE detected in the n-type thermoelectric semiconductor heterostructure PbTe, make it possible to obtain the magnitude of the generated voltage of near 0.06 V in the medium temperature mode.

Conclusion. The achieved results exceed the previously known ones and give grounds to continue research with the aim of developing semiconductor converters operating on the basis of TVE.

1. Kaminskii V. V., Solov'ev S. M. The Emergence of an Electromotive Force with a Change in the Valency of Samarium Ions During the Phase Transition in SmS Single Crystals. Semiconductors/Physics of the Solid State. 2001, vol. 43, iss. 3, pp. 423-426. Available at: http://www.ioffe.rssi.ru/journals/ftt/2001/03/p423-426.pdf (accessed 15.12.2019) (In Russ.)

2. Groshev I., Polukhin I. Samarium Sulfide and the Latest Developments on its Basis. Components & Technologies. 2014, no. 8, pp. 150-157. Available at: https://www.kit-e.ru/articles/device/2014_8_150.php (accessed 19.12.2019) (In Russ.)

3. Strelov V. I., Baskakov E. B., Bendryshev Yu. N., Kanevskii V. M. Features of Obtaining Thin Films for Thermal Converters Based on SmS. Kristallografiya [Crystallography]. 2019, vol. 64, no. 2, pp. 281-284. doi: 10.1134/S0023476119020292 (In Russ.)

4. Kaminskii V. V., Lebedev A. O., Solov'ev S. M., Sharenkova N. V. SmS/SiC Heterostructure and Its Associated Thermovoltaic Effect. Technical Physics. 2019, vol. 64, iss. 2, pp. 181-182. doi: 10.1134/S1063784219020075

5. Kalinin Yu. E., Chuiko A. G., Novikov E. G. Prospects of Development of Thermoelectric and Thermovoltaic Materials. Alternative Energy and Ecology (ISJAEE). 2015, no. 3, pp. 28-39. Available at: https://www.isjaee.com/jour/article/view/12 (accessed 19.12.2019) (In Russ.)

6. Pronin I., Yakushova N., Averin I., Karmanov A., Moshnikov V., Dimitrov D. Development of a Physical Model of Thermovoltaic Effects in the Thin Films of Zinc Oxide Doped with Transition Metals. Coatings. 2018, vol. 8, no. 12, pp. 433(1-12). doi: 10.3390/coatings8120433

7. Pronin I. A., Averin I. A., Bozhinova A. S., Georgieva A. Ts., Dimitrov D. Ts., Karmanov A. A., Moshnikov V. A., Pa-pazova K. I., Terukov E. I., Yakushova N. D. Thermovoltaic Effect in Zinc Oxide Inhomogeneously Doped with Variable Valence Impurities. Pis'ma v ZhTF [Letters to the Journal of Technical Physics]. 2015, vol. 41, iss. 19, pp. 22-28. Available at: https://journals.ioffe.ru/articles/viewPDF/42354 (accessed 15.12.2019) (In Russ.)

8. Pronin I. A., Yakushova N. D., Dimitrov D. Ts., Krasteva L. K., Papazova K. I., Karmanov A. A., Averin I. A., Georgieva A. Ts., Moshnikov V. A., Terukov E. I. A New Type of Gas Sensors Based on the Thermovoltaic Effect in Zinc Oxide Inhomogeneously Doped with Variable Valence Impurities. Pis'ma v ZhTF [Letters to the Journal of Technical Physics]. 2017, vol. 43, iss. 18, pp. 11-16. doi: 10.21883/PJTF.2017.18.45028.16754 (In Russ.)

9. Saidov N. S., Saidov A. S., Usmonov Sh. N., Amon-ov K. A. Thermovoltaic Effect of pSi-n(Si2)1-x(ZnS)x Structures. Geliotekhnika. 2009, no. 4, pp. 102-104. Available at: http://geliotekhnika.uz/ru/articles/572 (accessed15.12.2019) (In Russ.)

10. Saidov A. S., Leiderman A. Yu., Karshiev A. B. Thermovoltaic Effect in a Graded-Gap Solid Solution Si1-xGex (0< x< 1). Pis'ma v ZhTF [Letters to the Journal of Technical Physics]. 2016, vol. 42, iss. 14, pp. 21-27. Available at: http://journals.ioffe.ru/articles/viewPDF/43410 (accessed 15.12.2019). (In Russ.)

11. Leyderman A. Yu., Saidov A. S., Khashaev M. M., Rahmonov U. K. Thermovoltaic Synergetic Effects of SelfOrganization of Impurities and Defects in Semiconductors of Type AIIIBV. Alternative Energy and Ecology (ISJAEE). 2015, no. 7, pp. 55-69. doi: 10.15518/isjaee.2015.07.004 (In Russ.)

12. Kaminskii V. V., Golubkov A. V., Vasil'ev L. N. Defective Samarium Ions and the Effect of the Generation of an Electromotive Force in SmS. Semiconduc-tors/Physics of the Solid State. 2002, vol. 44, iss. 8, pp. 1501-1505. Available at: http://journals.ioffe.ru/articles/viewPDF/39644 (accessed 15.12.2019) (In Russ.)

13. Hickey C. F., Gibson U. J. SmS Phase Transition in Thin Films Prepared by Reactive Evaporation. Phase Transitions: A Multinational Journal. 1989, vol. 14, iss. 1-4, pp. 187-199. doi: 10.1080/01411598908208095

14. Andreev O. V., Ivanov V. V., Gorshkov A. V., Mio-dushevskiy P. V., Andreev P. O. Chemistry and Technology of Samarium Monosulfide. Eurasian Chemico-Tech-nological Journal. 2016, vol. 18, no 1, pp. 55-65. doi: 10.18321/ectj396

15. Mott N. F., Davis E. A. Electronic Processes in NonCrystalline Materials. Moscow, Mir, 1982, 658 p. (In Russ.)

16. Miodushevskii P. V., Andreev P. O., Vysokikh A. S. Phase Composition of the Surface Layer of Samarium Monosulfide Samples. Herald of Omsk University, 2011, no. 4, pp. 122-126. (In Russ.)