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Study of optical absorption in TlGaSe2:Zn2+ single crystals

1Makhnovets G.V., 1Myronchuk G.L., 2Piskach L.V., 
1Vidrynskyi B.V. and 1Kevshyn A.H.

1Department of Physics, Lesya Ukrainka Eastern European National University,   13 Voli Avenue, 43025 Lutsk, Ukraine
2Department of Inorganic and Physical Chemistry, Lesya Ukrainka Eastern   European National University, 13 Voli Avenue, 43025 Lutsk, Ukraine

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Abstract. We report the results of experimental studies for the optical absorption in TlGaSe2:Zn2+ single crystals grown using a modified Bridgman–Stockbarger technique. The absorption measurements at different temperatures are performed with the steps 50 K. The analysis of the experimental data yield in the absorption coefficients of TlGaSe2:Zn varying from 20 to 800 cm–1 in the temperature region 100–300 K. Direct and indirect bandgap values for TlGaSe2:Zn2+ are calculated as functions of temperature. These values are respectively equal to 2.22 and 2.04 eV at 100 K. It is revealed that the spectral dependences of the absorption coefficient in the region 60–130 cm–1 follow the Urbach rule, whereas the corresponding steepness parameter and the Urbach energy increase with increasing temperature.

Keywords: chalcogenides, Urbach energy, direct and indirect bandgaps, steepness parameter

PACS:  42.25.Bs
UDC: 535.343.2
Ukr. J. Phys. Opt. 19 49-59
doi: 10.3116/16091833/19/1/49/2018
Received: 19.12.2017

Анотація. Представлено результати експериментальних досліджень оптичного поглинання монокристалів TlGaSe2:Zn2+, вирощених за модифікованим методом Бріджмена–Стокбаргера. Вимірювання поглинання при різних температурах виконано з кроком 50 К. Аналіз даних показав, що коефіцієнт поглинання TlGaSe2:Zn змінюється в межах від 20 до 800 см–1 у температурному діапазоні 100–300 К. Прямі та непрямі величини ширини забороненої зони розраховано як функції температури. За температури 100 К ці параметри складають відповідно 2,22 і 2,04 еВ. Встановлено, що спектральні залежності коефіцієнта поглинання в області 60–130 см–1 описуються правилом Урбаха, а відповідний параметр крутизни краю поглинання та енергія Урбаха зростають зі зростанням температури. 
 
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