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KMID : 1159320160180030345
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Korean Journal of Vision Science
2016 Volume.18 No. 3 p.345 ~ p.351
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Estimation of Thermodynamic Functions from the Optical Energy Band Gaps' Dependence of Ga2Se3 and Co-doped Ga2Se3 Single Crystals on Temperature
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Lee Young-Hwan
Youn Jae-Tae
Park Kwang-Ho
Kim Duck-Tae
Hyun Seung-Cheol
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Abstract
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Purpose: We have investigated the optical energy band gaps' dependence of Ga2Se3 and Ga2Se3 : Co2+ single crystals grown by Chemical Transport Method on temperature. As results of these, we could estimate thermodynamic functions.
Methods: We made the quartz ampoules for growing Ga2Se3 and Ga2Se3 : Co2+ single crystals with Ga(6N, 2 mol), Se(6N, 3 mol), Co(4N, 0.1 mol%) and transporting agent I(6N, 6㎎/㎤) under 5 ×10-5 torr. Positioned the ampoule in the middle of the two zones furnace and eliminated the residual impurities from the growing site. For growing Ga2Se3 and Ga2Se3 : Co2+ single crystals, we maintained 6 days at 890℃ in the starting site and 780℃ in the growing site, respectively. To obtain the temperature dependence of the energy band gaps near the fundamental absorption edge,
we measured the optical absorption spectra by using UV-VIS-NIR spectrophotometer(Hitachi,
U-3501) with cryostat(Air Products, SH-4).
Results and Consideration: The optical absorption spectrum of Ga2Se3 and Ga2Se3 : Co2+ single crystals was increased abruptly at 576 ㎚ and 594 ㎚ region, respectively. Also, the temperature dependence of the energy band gaps was estimated from the Varshni equation.
Conclusions: The grown single crystals had cubic structures and the lattice constants were a = 5.442 Å and 5.672 Å for Ga2Se3 and Ga2Se3 : Co2+ single crystals, respectively. The optical energy band gaps obtained from the optical absorption spectra were direct transition types. The temperature dependence of the energy band gaps was applied well to Varshni equation and it was given that Eg(0) = 2.177 eV, α= 7.8 ×10-4 eV/K, β= 378 K and Eg(0) = 2.069 eV, α= 1.2 ×10-3
eV/K, β= 349 K for Ga2Se3 and Ga2Se3 : Co2+ single crystals, respectively. And the thermodynamic functions, entropy(SCV), heat capacity(CCV), and enthalpy(HCV), could be estimated from the temperature dependence of the optical energy band gaps.
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KEYWORD
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Chemical Transport Method, UV-VIS-NIR spectrophotometer, Energy band gap, Entropy(SCV), Heat capacity(CCV), Enthalpy(HCV)
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