Analysis of the fundamental absorption edge of the films obtained from the C₆₀ fullerene molecular beam in vacuum and effect of internal mechanical stresses on it

Nanostructures with fullerene C₆₀ were obtained using vacuum sublimation thermal C₆₀ fullerene powder onto unheated substrates made of silicon, mica, silica and coverslip glass. The effect of the structure, composition and mechanical stresses in the films on fundamental absorption, density-of-states tails in them were investigated by Ramаn spectroscopy, atomic force microscopy, light absorption, electroreflectance modulation spectroscopy and measuring the bend of heterosystems. Ascertained in this work has been the origin of variation observed in literature data concerning the width of the band gap Eg between 1.48 to 2.35 eV and the nature of the fundamental absorption edge in solid C₆₀. This variation is related with decomposition of fullerene molecules caused by the increase in temperature of sublimation. It has been found that C₆₀ in the crystalline state is direct band-gap semiconductor with Eg close to 1.6 eV in the singular point X of the Brillouin zone. The electroreflectance spectra of films and heterosystems bending were used to calculate the Eg dependence on the internal mechanical stresses. The respective coefficient value is equal to –2.8 10⁻¹⁰ eV/Pa

Ge/GaAs(100) Thin Films: Large Effect of Film Growth Rate and Thicknesses on Surface Morphology, Intrinsic Stresses and Electrical Properties

We found out and studied a profound effect of film growth rate on the electrical properties, intrinsic stresses and surface morphology of thin Ge films grown on GaAs(100). This effect is essential and has to be accounted for when developing and producing devices based on the Ge/GaAs heterostructure. All the Ge films under investigation were single-crystalline and epitaxially-grown on the GaAs(100) substrates. However, the transport phenomena in Ge films grown at low and high deposition rate differed drastically. Those obtained at low deposition rate were p-type and high resistant. They had a low concentration of free charge carriers and thermally activated conductivity, which is characteristic of heavily doped and strongly (in the limiting case, fully) compensated semiconductors. Although such films were single-crystalline, their conductivity was percolation-type. The Ge films obtained at high deposition rate were n-type and low resistant. They had high concentration of free charge carriers. The temperature dependence of conductivity in such films was weak or practically absent, which is characteristic of degenerate heavily doped semiconductors. Besides, the surface morphology cardinally differed for films obtained at low and high deposition rate. At low film growth rates, surfaces with developed relief were observed whose valleys and ridges formed grains of irregular shape with pronounced substructure. As the film thickness grew, the surface relief became essentially pronounced. At rather high film deposition rates, contrary to the above, the Ge film surface was fine-grained and smooth; the surface relief practically did not depend on the film thickness. As the deposition rate went down, the intrinsic stresses in films essentially decreased. The results obtained were analyzed from the viewpoint of formation of compositional and morphological inhomogeneities, and fluctuations of electrostatic potential at low growth rates. Such potential fluctuations modulate Ge energy bands leading to appearance of potential relief and deep tails of density of states in the Ge bandgap. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3506

Electroreflectance spectroscopy and scanning electron microscopy study of microrelief silicon wafers with various surface pretreatments

The effect of various pretreatments on the performance of microrelief (textured) Si wafers was studied by the techniques of low-field electroreflectance spectroscopy, scanning electron microscopy, and electron diffraction. Four types of preliminary treatments were employed to prepare microrelief surfaces by anisotropic chemical etching: (i) cutting, (ii) cutting and mechanical polishing with Al₂O₃, (iii) cutting and chemical polishing with HNO₃:HF, and (iv) the standard industrial technique. Using the critical point energy Eg at the central point in the Brillouin zone (GIV₂₅ – GC₁₅ transition) and the phenomenological parameter of broading G to characterize the performance of the Si surface, it was found that anisotropic chemical etching performed after cutting produced the surface performance comparable to that of industrially fabricated wafers, but at a lower cost.Методами спектроскопії низькопольового електровідбиття, растрової електронної мікроскопії та електронографії досліджено вплив попередніх обробок поверхні кремнію (різка; різка та механічна поліровка; різка та хімічна поліровка; стандартна фабрична обробка) на досконалість анізотропно травлених мікрорельєфних пластин. Як критерій досконалості аналізуються енергія критичної точки Eg в центрі зони Бріллюена (переходи GIV₂₅ – GC₁₅ ), феноменологічний параметр уширення Г, рухливість носіїв заряду, морфологічні особливості поверхні та кристалічна структура. Показана можливість використання попередньої обробки різкою для виготовлення достатньо досконалих анізотропно травлених мікрорельєфних пластин. При цьому очікується зменшення їх кошторису.Методами спекроскопии низкополевого электроотражения, растровой электронной микроскопии и электронографии исследовано влияние предварительных обработок поверхности кремния (резка; резка и механическая полировка; резка и химическая полировка; стандартная фабричная обработка) на совершенство анизотропно травленных микрорельефных пластин. В качестве критерия совершенства анализируются энергия критической точки Eg в центре зоны Бриллюэна (переходы GIV₂₅ – GC₁₅, феноменологический параметр уширения Г, подвижность носителей заряда, морфологические особенности поверхности и кристаллическая структура. Сделан вывод о возможности использования предварительной обработки резкой для получения достаточно совершенных анизотропно травленных микрорельефных кремниевых пластин. При этом ожидается снижение стоимости пластин

Investigation of the undersurface damaged layers in silicon wafers

The undersurface damaged layers of the silicon wafers were studied by electroreflectance method. These damaged layers could be created at cutting or standard treatment (ST) of the silicon wafers. The silicon substrates were layer by layer etched in the polishing etching solution for investigation of the undersurface damaged layers. Surface and undersurface layers were qualified by the phenomenological parameter of broadening (PPB) from the electroreflectance spectra. The concealed undersurface damaged layers with thickness 25 µm were observed on the ST samples. The PPB decreased with exponential rule for the samples after cutting and achieved the permanent value on the depth 125 µm

Effects of interband phototunneling and filling the bands in electroreflectance spectra of germanium

Electroreflectance spectra of chemically etched (110) surface of intrinsic germanium are measured in the range of E₁, E₁ + Δ₁ transitions for ||[100] and ||[10] directions of the polarization vector. Separated are isotropic (surface) and anisotropic (bulk) electroreflectance components. The spectrum of the bulk electroreflectance component (the Keldysh-Franz effect), as it can be deduced from its phase, corresponds to the case when energy bands are bent up if going to the surface. This situation is possible in the conditions of filling the bands only at presence of an extremum in the semiconductor energy scheme. Appearance of this extremum can be related to the fact that the electron wave function at the surface is equal to zero or defermined by mirror image force action

Quantum-size effects in semiconductor heterosystems

Created on the basis of Si, GaAs and C60 fullerenes were low-dimensional heterostructures with a surface quantum-size effect at the film-substrate interface. There have been defined technological conditions of its appearance. Using modulation electroreflectance spectroscopy, calculated were spectral broadening parameters, the energy relaxation time of excited light charge carriers, the energy of quantized levels and the width of the quantum wells

Influence of neutron irradiation on elctrooptical and structural properties of silicon

Processes of structure defects formation, which accompanied by oxygen precipitation after a neutron irradiation (10¹⁵- 10¹⁹ n/cm²) and high-temperature treatment (800 - 1000°С) in CZ silicon, were investigated by the transmission electron microscopy. Influence of the structure defects on electrooptical properties of silicon was revealed