Calculation of Fermi level location and point defect ensemble in CdTe single crystal and thin films

With the use of expressions obtained from the “first principles”, the ensemble of point defects was calculated, and the location of a Fermi level in undoped cadmium telluride single crystals and thin films depending on physico-technological conditions of their fabrication and annealing is determined. The model in use accounts the most complete spectrum of defects in chalcogenide, including defects in the cadmium and tellurium sublattices, and the existence of an antistructural defect on the cadmium sublattice. Calculations of the concentration of neutral and charged defects are realized for two extreme cases – full equilibrium and quenching. The comparison of the obtained results with the data of modeling provided with the use of a quasichemical formalism for a number of models most used presently is carried out. It is shown that all models describe well the results of Hall measurements of the concentration of free carriers in single crystals in the range of high cadmium pressure, but give essentially different results in the range of high tellurium pressure. Dominant defects in single crystals at high cadmium pressure and annealing temperatures are twice charged tellurium vacancies or interstitial cadmium atoms, which is in agreement with experimental results, as just such defects can provide the dependence of the concentration of free carriers on cadmium pressure as n ~ P¹/³Cd . A type of defects which are dominant in a tellurium-enriched material is determined by the chosen model. This allows us to make conclusions about the validity of the considered models and to specify the thermodynamic parameters of the defect creation processes in a material. The offered model can be used for modeling the ensemble of point defects in any А₂В₆ compounds. Thus, the problem of the choice of models adequate to experimental data is reduced to the determination of the creation energy for uncharged defects and the depth of energy levels of charged defects

Structural Properties of the SnxSy Films Obtained by the Thermal Vacuum Co-evaporation

The present work deals with the study of the structural properties of the SnxSy thin films deposited by the closed-spaced vacuum co-evaporation (CSVCE) method. Calculation of temperature dependencies of the sulfur and tin vapor pressures allows to estimate growth conditions of the films with the stoichiometric composition. The effect of growth conditions on surface morphology and structural properties of SnxSy films were studied. Surface morphology of obtained films was determined by the scanning electron microscope (SEM-102Е). Structural investigations of the films were performed with the X-ray diffraction (XRD) method. The analysis of chemical composition of the layers was carried out by the scanning electron microscope by energy dispersive X-ray (ЕDAX) spectroscopy. Influence of the substrate temperature on chemical composition of thin films and their structural characteristics was also investigated

Effect of Substrate Temperature on the Structural Properties of CdxZn1-xTe Films Grown by Close-Spaced Sublimation Method

In this work by energy dispersive analysis of X-rays, scanning electron microscopy and X-ray diffraction methods films of CdxZn1-xTe solid solution, obtained by a close-spaced vacuum sublimation technique under different temperatures of glass substrate, has been studied. Films were deposited by the co sublimation of Cadmium Telluride (CdTe) and Zinc Telluride (ZnTe) chunks, mixed in the ratio of 2:1. The effect of substrate temperature on the surface morphology, elemental and phase composition, lattice parameter, scattering domain sizes has been studied. The results of these studies can be used for obtaining absorber layers of tandem solar cells, basic layers of X-ray and gamma detectors

Effect of Substrate Temperature on the Structural Properties of CdxZn1-xTe Films Grown by Close-Spaced Sublimation Method

In this work by energy dispersive analysis of X-rays, scanning electron microscopy and X-ray diffraction methods films of CdxZn1-xTe solid solution, obtained by a close-spaced vacuum sublimation technique under different temperatures of glass substrate, has been studied. Films were deposited by the co sublimation of Cadmium Telluride (CdTe) and Zinc Telluride (ZnTe) chunks, mixed in the ratio of 2:1. The effect of substrate temperature on the surface morphology, elemental and phase composition, lattice parameter, scattering domain sizes has been studied. The results of these studies can be used for obtaining absorber layers of tandem solar cells, basic layers of X-ray and gamma detectors

Structural and electrical properties of ZnS/CdTe and ZnTe/CdTe heterostructures

We investigated the structural, substructural and electrical properties of ZnS/CdTe and ZnTe/CdTe heterostructures obtained by the close-spaced vacuum sublimation. It was found that the structural properties of CdTe and ZnTe thin films deposited on ZnS or CdTe sublayers are better than those of the films obtained on glass substrate at the same growth conditions. XRD-analysis has shown that Zn(x)Cd(1- x)Te(x = 0.21-0.30) solid solutions having the cubic phase were formed near the films’ interfaces. Furthermore, the saturation current, the ideality factor and the value of the potential barrier height were determined by the analysis of dark currentevoltage characteristics. This makes it possible to establish optimal growth conditions of ZnS/CdTe heterojunctions. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3016

Ensemble of point defects in CdTe single crystals and films in the case of full equilibrium and quenching

The ensemble of point defects in CdTе undoped single crystals has been modeled. Two extreme cases were calculated: full equilibrium and quenching. Dependences of the point defect and free carrier concentrations on technological parameters of growing, post-growth annealing in Cd vapor, and the sample examination temperature have been studied. The growth conditions of single crystals and n- and p-type conductivity CdTе films were defined. The results obtained have been compared with experimental data. This made it possible to make conclusions concerning validity of the studied models and to propose additional experiments to make final choice between them.Проведено моделирование ансамбля точечных дефектов в нелегированных монокристаллах и пленках теллурида кадмия. Расчеты выполнены для двух крайних случаев - полного равновесия и закалки дефектов. Получены зависимости концентрации собственных дефектов, свободных носителей заряда от технологических параметров выращивания, послеростового отжига в парах кадмия и температуры исследования образцов. Определены условия изготовления монокристаллов и пленок CdTе n- и p-типа проводимости. Проведено сравнение полученных результатов с экспериментальными данными, что позволило сделать выводы относительно обоснованности рассмотренных моделей и предложить дополнительные эксперименты, позволяющие сделать окончательный выбор между ними.Проведено моделювання ансамблю точкових дефектiв у нелегованих монокристалах i плiвках телуриду кадмiю. Розрахунки виконано для двох крайнiх випадкiв - повної рiвноваги i загартування дефектiв. Одержано залежностi концентрацiї власних дефектiв, вiльних носiїв заряду вiд технологiчних параметрiв вирощування, пiсляростового вiдпалу у парах кадмiю i температури дослiдження зразкiв. Визначено умови виготовлення монокристалiв i плiвок CdTе n i p-типу провiдностi. Проведено порiвняння отриманих результатiв з експериментальними даними, що дозволило зробити висновки щодо обгрунтованостi розглянутих моделей i запропонувати додатковi експерименти, якi дозволяють зробити остаточний вибiр мiж ними

Structural and microstructural properties of Cd₁-xZnxTe films deposited by close spaced vacuum sublimation

The structural properties (microstresses, texture, lattice parameter, coherent scattering domains size) and chemical composition of Cd₁₋xZnxTe (CZT) films with variable zinc concentration were studied. Films were deposited on molybdenum coated glass substrates by close spaced vacuum sublimation method. Properties of samples were investigated by X-ray diffraction, energy dispersive spectroscopy, scanning electron microscopy. Zinc concentration in CdZnTe layers was determined by the EDS and from the lattice parameter, according to the literature data. Namely, it was determined that the CZT films had following Zn concentrations: x = 0.09, x = 0.24, x = 0.30