Dinara Dallaeva

Morphological features in aluminum nitride epilayers prepared by magnetron sputtering

Abstract The aim of this study is to characterize the surface topography of aluminum nitride (AlN) epilayers prepared by magnetron sputtering using the surface statistical parameters, according to ISO 25178-2:2012. To understand the effect of temperature on the epilayer structure, the surface topography was investigated through atomic force microscopy (AFM). AFM data and analysis of surface statistical parameters indicated the dependence of morphology of the epilayers on their growth conditions. The surface statistical parameters provide important information about surface texture and are useful for manufacturers in developing AlN thin films with improved surface characteristics. These results are also important for understanding the nanoscale phenomena at the contacts between rough surfaces, such as the area of contact, the interfacial separation, and the adhesive and frictional properties.

Characterizing SiC-AlN semiconductor solid solutions with indirect and direct bandgaps

The objective of the study is to characterize the dependence of the optical properties of solid solutions of silicon carbide and aluminum nitride on composition. Even small differences in composition provide manipulation of band gap features over a wide range. Data for this paper were collected by X-ray diffraction, photoluminescence and absorption spectroscopy. The evolution of the observed optical properties as a result of compositional changes were studied. X-ray studies confirm the presence of a(SiC)1-x(AlN)x solid solution. Investigation of absorption spectra shows the optical band gap of the sample with composition (SiC)0,88(AlN)0,12 is 3.5eV, and 4.24 eV for the (SiC)0,36(AlN)0,64 solid solution. The photoluminescence spectra demonstrate the strong dependence of the spectra on composition x. The experimental results are in agreement with theory. These data demonstrate the optimization of optical properties for particular optoelectronic applications by varying the (SiC)1-х(AlN)х composition.

AFM imaging of natural optical structures

The colors of some living organisms assosiated with the surface structure. Irridesence butterfly wings is an example of such coloration. Optical effects such as interference, diffraction, polarization are responsible for physical colors appearance. Alongside with amazing beauty this structure represent interest for design of optical devices. Here we report the results of morphology investigation by atomic force microscopy. The difference in surface structure of black and blue wings areas is clearly observed. It explains the angle dependence of the wing blue color, since these micrometer and sub-micrometer quasiperiodical structures could control the light propagation, absorption and reflection.

Realization of microscale detection and localization of low light emitting spots in monocrystalline silicon solar cells

We report on detection and localization of imperfections in silicon solar cell bulk and surface with sub-micrometer resolution. To obtain this resolution, a family of imaging techniques including SNOM, SEM and AFM is often separately used for this purpose. In this paper we combine several of these proximal methods together, because each of them brings complimentary information about the imperfection. First, we note that SNOM images often contain distortions due to the interaction of the probe tip and sample. Therefore, we look for the possibility to circumvent this weakness and obtain more realistic images. In our experiments, we take advantage of the fact that defects or imperfections in silicon solar cell structures under reverse-bias voltage exhibit microscale low light emitting spots, and we apply an improved SNOM measurement to localize these spots. As a result, this system allows a localization and measurement of low light emission on microscale. Consequently, the size and shape of imperfections can also be determined.

Investigation of optical properties of SiC/(SiC)1-x(AlN)x heterostructures

In this study the optical properties of SiC/(SiC)1-x(AlN)x heterostructures were investigated. The photoluminescence spectrum of (SiC)1-x(AlN)x samples at different temperatures and also the dependence of photoluminescence on wavelength of exciting light were studied. Absorption factor is defined using measured values of transmitting efficiency. The results of study of morphology and composition of obtained samples confirm growth regularity in single-crystal phase. It was observed that n-SiC/p-(SiC)1-x(AlN)x begins to shine at reverse voltage that a little exceed the voltage of irreversible breakdown.

SEM and AFM imaging of solar cells defects

The paper deals with the successive localization and imaging of solar cell defects, going from macroscale to microscale. For the purpose of localization, the light emission from reversed bias samples is used. After rough macroscopic localization, microscopic localization by scanning probe microscopy combined with a photomultiplier (shadow mapping) is performed. The type of microscopic defects are discernable from their current-voltage plot or from noise measurements. Two specific defects, both of the avalanche type, with different voltage threshold, are presented in this paper. Current voltage plots and radiant flux versus voltage characteristics for two temperatures, topography, shadow map and corresponding SEM micrographs are shown for both samples.

Local topography of optoelectronic substrates prepared by dry plasma etching process

In this work, the etch rate of silicon carbide and aluminum oxide were studied as a function of the angle etching material and flow of plasma. Al2O3 and SiC are important materials in the design of optical and electronic devices and the topography of the wafers has a large influence on the device quality. Argon was applied for the dry etching of Al2O3 and SiC wafers. The wafer slope for highest obtained etch is defined. Atomic force microscopy was used to good morphology control of etched wafers. Statistical and correlation analysis was applied to estimate the surface perfection. Interferometry allowed to control etching rate.

Interferometry and Atomic Force Microscopy of Substrates for Optoelectronics Proceeded by Dry Plasma Etching

The paper describes the process of sapphire and silicon carbide substrates preparation by dry plasma etching and its characterization. The study confirms the possibility of using dry plasma etching processes for wide band gap materials treatment, since the condition of the substrate surface is an important parameter for electronic and optoelectronic devices manufacturing. Processed substrates were studied by interferometry to define the etch depth, and by atomic force microscopy to study the topography and statistical analysis of surface roughness before and after etching. The interferometry reveals the dependence of etch rate on the angle between the substrates and defocused beam of argon ions. It is also shown in low scale image that the surface damage occurs after the substrate treatment. But the common large area surface topography indicates the decreasing of roughness. In order to have purely physical etching the argon plasma was used. Thus this combination of methods allows determine optimal conditions of the substrate preparation.

Dielectric properties of epoxy resins with oxide nanofillers and their accelerated ageing

The aim of this paper is to discuss the impact of nanoparticles in epoxy matrix on dielectric parameters in the course of ageing. One of the directions pursued in the development of epoxy resins is the addition of nanofillers which act as efficient barriers for the propagation of electrical trees. In view of the prospects for the potential replacement of currently-used epoxy-based electric insulations with epoxy nanocomposites, it is necessary to know the behavior of such epoxy resins with nanofillers during aging. For this purpose, epoxy nanocomposites were exposed to accelerated aging and changes in dielectric properties were observed. Experimental samples were manufactured from bisphenol-A based epoxy resin for high voltage applications and oxide nanofillers. The volume of nanofiller added into epoxy resin was 1.5 wt %. Sample thickness was of the order of a few hundreds of μm. Complex permittivity (ε), inner resistivity (ρi) and loss factor (tan δ) were measured at temperatures from -153 °C to +167 °C and in the frequency range 10-2 to 106 Hz.

Cold field emission electrode as a local probe of proximal microscopes: Investigation of defects in monocrystalline silicon solar cells

Monocrystalline silicon is still very interesting material for solar cells fabrication due to its quality and external efficiency. Nevertheless during a tailoring of eligible silicon wafers, some inhomogeneities or irregularities emerge and provide defects which give trouble to good operation of solar panels. Generally, there are two classes of defects in silicon wafer: material defects due to imperfections or irregularity in crystal structure (point, line, square or volume defects), and defects induced by wafer processing. To avoid a use of damaged cells, macroscopic and microscopic measurement techniques must be applied. In this paper we present a microscopic method combining electrical noise measurements with scanning probe localization of luminous micro-spots defects. The paper brings experimental results showing local electric and optical investigations of defects in etched monocrystalline silicon solar cells and a use of cold field emission tungsten electrode as a local probe for apertureless scanni...