Polycrystalline and oriented films of barium disilicide (BaSi2) with a thickness of up to 100 nm were formed on silicon (111) substrates by high-temperature (800 ° C) solid-phase (single-stage and two-stage) annealing. The single phase of barium disilicide films and their semiconductor nature have been proven to be below 1.25 eV according to X-ray and optical spectroscopic methods. Two preferential orientations of the BaSi2 crystallites were detected and their orientation was determined in the films formed by two-stage annealing. According to the calculations of the parameters of the crystal structure of BaSi2 films, a compression of the unit cell volume from 2.7% to 5.13% was found, depending on the cooling time to room temperature. The stability of the films to laser radiation was studied by registering the Raman spectra with a variable power of laser radiation. The maximum power density of the laser beam (3⋅109 W/m2), which does not lead to the beginning of the destruction of these films, was determined.
BaSi2 thin films were formed on Si (111) substrate by solid-phase epitaxy (SPE) (UHV deposition) using the template technology followed by vacuum annealing at temperatures of 600 °C and 750 °C. After the deposition and annealing barium silicide films were characterized by Auger electron spectroscopy, grazing incidence x-ray diffraction (GIXRD) and atomic-force microscopy (AFM). It was established that the films annealed at T = 600 °C are polycrystalline with the structure of the orthorhombic BaSi2, with grain sizes of 100-200 nm. Higher anneal temperature (T=750 °C) leads to increase of diffraction peak intensity of BaSi2 phase with grain coagulation into 300-400 nm islands. It was confirmed that nanocrystalline BaSi2 films are characterized by a direct fundamental interband transition at 1.3 eV, the second interband transition with an energy of 2.0 eV, own phonon structure with wave number peaks at 112, 119, 146 and 208 cm-1 and a high density of defect states within the band gap, which provide a noticeable subband absorption at energies of 0.8 – 1.1 eV.
The search for inexpensive and efficient methods of forming thin BaSi2 films as a promising material for photovoltaic is an actual task. The co-deposition of Ba and Si atoms with alloy thickness of 100-120 nm on the silicon substrate at room temperature with following annealing (SPE method) was proposed. Ba-Si alloy compounds then were thermally annealed at different temperatures and three samples were formed: #1 at T = 600 ° C, #2 at T = 700 ° C and #3 at T = 800 ° C. Polycrystalline films with an orthorhombic BaSi2 structure were formed by XRD, UV-VIS, FIR and Raman spectroscopies data. BaSi2 grains in samples #1 and #2 have sizes 62-64 nm and 86 nm in the sample #3 from XRD data calculations by Scherrer formula. Proposed growth method resulted to strong compression of the BaSi2 unit cell volume on 1.78 – 2.70%. The strongest compression was observed after annealing at 800 °C, which was accompanied by desorption of a noticeable amount of barium and a strong decrease in the film thickness in the sample #3. The formation of nanosize Si clusters was confirmed by Raman data for samples #2 and #3, but they did not observed in the sample #3. So, the film, formed at 800 °C, is the most qualitative in terms of structure and single-phase BaSi2, but with strong decrease of initial Ba-Si alloy thickness due to Ba desorption.
Амурский государственный университет, г. Благовещенск В статье представлены результаты эксперимента по формированию методом твёрдофазной эпи-таксии тонких плёнок дисилицида бария (BaSi 2 ) -перспективного материала для солнечных элементов. Формирование BaSi 2 проводилось в условиях сверхвысокого вакуума на кремниевых подложках по тех-нологии template. На финальной стадии формирования наноструктур проводили рекристаллизацию плё-нок отжигом. Полученные тонкие плёнки исследовали in-situ методами: электронной оже-спектроскопии и спектроскопии характеристических потерь энергии электронами. Далее ex-situ методами: атомно-силовой микроскопии и рентгеновской дифракции. Последний метод показал наличие в плёнке, сформи-рованной при температуре рекристаллизации T = 800 0 С, a-ориентированного дисилицида бария. Для данной плёнки представлены спектры оже-электронов и характеристических потерь энергии электрона-ми. Анализ топологии поверхности полученной наноструктуры методом атомно-силовой микроскопии показал, что её шероховатость сопоставима с шероховатостью образцов тонких плёнок BaSi 2 , сформиро-ванных методом молекулярно-лучевой эпитаксии. Причина незначительного количества сформировав-шихся кристаллитов BaSi 2 -низкая взаимодиффузия атомов бария и кремния при выбранном методе формирования плёнки. Решение данной проблемы представляется в использовании технологии со-осаждения Ba и Si с последующей рекристаллизацией плёнки при температурах, близких к температуре, определённой в данной работе.Тонкие плёнки, нанотехнологии, солнечные ячейки, твёрдофазная эпитаксия, дисилицид бария, кремний.
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