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Документ Effect of aging on thermoelectric properties of the Bi2Te3 polycrystals and thin films(Науково-технологічний комплекс "Інститут монокристалів", 2021) Rogacheva, E. I.; Doroshenko, A. N.; Novak, K. V.; Sipatov, A. Yu.; Khramova, T. I.; Saenko, S. A.The temperature dependences (77-300 K) of the thermoelectric (TE) properties (the Seebeck coefficient S, electrical conductivity σ, Hall coefficient RH, Hall charge mobility μH>, and TE power factor P) were studied for freshly prepared and for exposed to air at room temperature during 5 years p-Bi2Te3 (60.0 at.% Te) and n-Bi2Te3 (62.8 at.% Te) polycrystals and thin films grown from them by thermal evaporation in vacuum. It was found that after aging, in the p- and n-Bi2Te3 bulk crystals and in the n-type film obtained from the n-Bi2Te3 crystal, type of conductivity is reserved but the p-type film obtained from the p-Bi2Te3 crystal, change the type of conductivity from hole to electronic. The activation energies of possible defect states were determined using the RH(T) dependences. After aging, at the temperatures close to room temperature, the p values of n-Bi2Te3 and p-Bi2Te3 polycrystals decreases by ~ 20 %, but p values of the n-type film grown from n-Bi2Te3 crystal increases by 20-30 %. In the p-type film obtained from p-Bi2Te3 polycrystal, and having changed the type of conductivity after aging, the p values exceed the p values of a film obtained from n-Bi2Te3 polycrystal by ~ 35 % at 250 K and by 25 % at 300 K, remaining at these temperatures below the p values for n-Bi2Te3 polycrystal after aging by ~ 15 %.Публікація Growth and structure of thermally evaporated Bi2Te3 thin films(Elsevier, 2016) Rogacheva, E. I.; Budnik, A. V.; Dobrotvorskaya, M. V.; Fedorov, A. G.; Krivonogov, S. I.; Mateychenko, P. V.; Nashchekina, O. N.; Sipatov, A. Yu.The growth mechanism, microstructure, and crystal structure of the polycrystalline nBi2Te3 thin films with thicknesses d = 15 – 350 nm, prepared by thermal evaporation in vacuum onto glass substrates, were studied. Bismuth telluride with Te excess was used as the initial material for the thin film preparation. The thin film characterization was performed using X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scan electron microscopy, and electron force microscopy. It was established that the chemical composition of the prepared films corresponded rather well to the starting material composition and the films did not contain any phases apart from Bi2Te3. It was shown that the grain size and the film roughness increased with increasing film thickness. The preferential growth direction changed from [00l] to [015] under increasing d. The X-ray photoelectron spectroscopy studies showed that the thickness of the oxidized surface layer did not exceed 1.5 – 2.0 nm and practically did not change in the process of aging at room temperature, which is in agreement with the results reported earlier for single crystals. The obtained data show that using simple and inexpensive method of thermal evaporation in vacuum and appropriate technological parameters, one can grow n-Bi2Te3 thin films of a sufficiently high quality.Документ Структура тонких пленок p-Bi₂Se₃, полученных термическим испарением в вакууме из одного источника(Інститут термоелектрики НАН України, 2015) Рогачева, Елена Ивановна; Будник, А. В.; Федоров, А. Г.; Кривоногов, С. И.; Матейченко, П. В.С использованием методов рентгеновской дифрактометрии, сканирующей электронной микроскопии, энергодисперсионной спектрометрии и атомной силовой микроскопии исследованы механизм роста, микроструктура и кристаллическая структура тонких пленок Bi₂Te₃ с толщинами d = 28-620 нм, полученных термическим испарением в вакууме кристаллов Bi₂Te₃ стехиометрического состава на стеклянные подложки. Полученные тонкие пленки были поликристаллическими, обладали р-типом проводимости и не содержали других фаз, кроме Bi₂Te₃. Показано, что с увеличением толщины пленок размер кристаллитов увеличивается до ~ 700-800 нм. Установлено, что преобладающим направлением роста кристаллитов является направление [00l], соответствующее направлению тригональной оси С₃ в гексагональной решетке. С увеличением толщины пленок свыше ~ 200-250 нм наряду с отражениями от плоскостей (00l) появляются отражения от других плоскостей, свидетельствующие о некоторой разориентации кристаллитов. Полученные результаты показывают, что, используя простой и недорогой метод термического испарения из одного источника и оптимальные технологические параметры, можно получить тонкие пленки p-Bi₂Te₃ достаточно высокого качества.Публікація Transport properties of the bismuth telluride thin films with different stoichiometry in the temperature range 77-300 K(Науково-технологічний комплекс "Інститут монокристалів", 2020) Rogacheva, E. I.; Novak, K. V.; Doroshenko, A. N.; Nashchekina, O. N.; Budnik, A. V.The objects of the present study are thin films with thicknesses d = 45-620 nm prepared by thermal evaporation in vacuum from a single source, using undoped p- and n-type Bi₂Te₃ polycrystals with different stoichiometry (60.0 and 62.8 at. % Te, respectively) as a charge, and subsequent condensation on glass substrates at 500 K. The temperature dependences of the Hall coefficient Rн, electrical conductivity σ, and Hall charge carrier mobility μн of thin films were obtained in the range 77-300 K. It was found that the films had the same type of conductivity as the initial polycrystals in the entire temperature range studied and, like in the initial crystals, σ and μн decreased with increasing temperature. The exponents ν in the μн(T) dependences for the bulk polycrystals were larger than those for the films and increased with increasing d. In contrast to the p-type bulk polycrystals, Rн of the p-type films decreased under increasing temperature. In the n-type Bi₂Te₃, Rн decreased with temperature for both thin films and bulk crystals, however, the character of the Rн(T) dependences for the crystals and films differed. The decrease in Rн with temperature before the range of intrinsic conductivity in all thin films is attributed to the existence of donor and acceptor defect states.Документ Structure of p-Bi₂Te₃ thin films prepared by single source thermal evaporation in vacuum(2015) Rogacheva, E. I.; Budnik, A. V.; Fedorov, A. G.; Krivonogov, A. S.; Mateychenko, P. V.The growth mechanism, microstructure, and crystal structure of thin Bi₂Te₃ films with thicknesses d = 28 - 620 nm prepared by thermal evaporation of stoichiometric Bi₂Te₃ crystals in vacuum onto glass substrates were studied using X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and atomic force microscopy. The obtained thin films were polycrystalline, exhibited p-type conductivity and did not contain any other phases except for Bi₂Te₃. It was shown that with increasing film thickness, the crystallite size increased up to ~ 700-800 nm. It was established that the preferential orientation of crystallite growth was [00l] direction corresponding to a trigonal axis С3 in hexagonal lattice. When the film thickness exceeded ~ 200-250 nm, along with reflections from (00l) planes, reflections from other planes appeared, which indicated a certain disorientation of crystallites. The results obtained show that using a simple and inexpensive method of thermal evaporation from a single source and choosing optimal technological parameters, one can grow thin p-Bi₂Te₃ films of sufficiently high quality.