S.N. Sahu

Bio: S.N. Sahu is an academic researcher. The author has contributed to research in topics: Crystallite & Vacancy defect. The author has an hindex of 2, co-authored 2 publications receiving 34 citations.

Study of structure and optical properties of GaAs nanocrystalline thin films

Abstract: Nanoparticulate thin films of GaAs we electrochemically prepared from acidic solutions of pure metallic Ga and As 2 O 3 . Samples of different crystallite sizes were prepared by varying the electrolysis parameters. Structural characterization of the nanoparticles were carried out by XRD technique which exhibits partial amorphization of the crystallites in the low electrolysis current regime. Quantum confinement effect was prominently observed in the optical absorption spectra with blue-shift of absorption onsets with respect to the bulk band gap. Room temperature photoluminescence exhibit band edge luminescence as well as other surface related bands. Incorporation of transition element as impurity leads to enhanced luminescence intensity and generates deep traps.

Orthorhombic-phase GaAs nanoparticles prepared by an electrochemical technique

Abstract: GaAs nanoparticles have been deposited on the indium tin oxide-coated glass substrate by the electrodeposition technique at 275 K. Transmission electron microscope micrographs show the isolated particles with diameters ranging from 11 to 21 nm and the connected particles having larger sizes. Selected area diffraction patterns contain spotty rings showing the polycrystalline nature of the GaAs nanocrystals. The interplanar spacings, determined from the electron diffraction pattern and the high-resolution lattice image, correspond to that of the orthorhombic GaAs(III) phase normally observed under high pressure. Two broad peaks corresponding to the above phase have been detected in the X-ray diffraction spectra. Micro-Raman measurement at 300 K shows a defect-activated phonon mode occurring at about 250 cm −1 , assigned to a point defect created due to the arsenic vacancy. The above vacancy arises during the transition from the six-fold co-ordination to the four-fold co-ordination phase.

Electronic states of semiconductor clusters : Homogeneous and inhomogeneous broadening of the optical spectrum

Abstract: The homogeneous (single-cluster) and inhomogeneous contributions to the low temperature electronic absorption spectrum of 35-50 ? diameter CdSe clusters are separated using transient photophysical hole burning. The clusters have the cubic bulk crystal structure, but their electronic states are strongly quantum confined. The inhomogeneous broadening of these features arises because the spectrum depends upon cluster size and shape, and the samples contain similar, but not identical, clusters. The homogeneous spectrum, which consists of a peak 140 cm -1 (17 meV) wide, with a phonon sideband and continuum absorption to higher energy, is compared to a simple molecular orbital model. Electron-vibration coupling, which is enhanced in small clusters, contributes to the substantial broadening of the homogeneous spectrum. The inhomogeneous width of the lowest allowed optical transition was found to be 940 cm -1 , or seven times the homogeneous width, in the most monodisperse sample.

Hysteresis loops and compensation behavior of cylindrical transverse spin-1 Ising nanowire with the crystal field within effective-field theory based on a probability distribution technique

Abstract: We investigate the effect of a transverse field on a cylindrical core/shell spin-1 Ising nanowire, within the effective-field theory based on a probability distribution technique, in order to clarify how the relevant thermodynamic quantities such a magnetizations, hysteresis loops, compensation behaviors, are influenced by a transverse field. From these studies, following interesting phenomena are found. (i) Beside a singly hysteresis loop, double, triple or even quadruple hysteresis loops occurs in the system. (ii) The P and N types of compensation behavior are obtained in addition to the Q-, R- and S-types. We also compare our results with some experimental and theoretical results and find in a qualitatively good agreement.

Nanoscale Growth of GaAs on Patterned Si(111) Substrates by Molecular Beam Epitaxy

Abstract: High-quality and defect-free GaAs were successfully grown via molecular beam epitaxy on silicon dioxide patterned Si(111) substrates by a two-step growth technique. Compared with the one-step approach, the two-step growth scheme has been found to be a better pathway to obtain a superior-quality GaAs on Si. Taking advantages of low energy for both Si(111) surface and GaAs/Si(111) interface, the two-step grown GaAs of total ∼175 nm atop patterned Si(111) substrates exhibits atomically smooth surface morphology, single crystallininty and a remarkably low defect density. A low-temperature GaAs nucleation layer of the two-step growth helps relieve the misfit stress by accommodating the misfit dislocations at the very adjacent GaAs/Si interface. The excellent properties of the two-step grown GaAs were investigated and verified by field-emission scanning electron microscopy, atomic force microscopy, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. Finally we demonstrated a GaAs on Si ...

Performance analysis of GaAs based solar cells under gamma irradiation

Abstract: The influence of gamma irradiation on gallium arsenide based photovoltaic cells was investigated. This type of solar cell is used for advanced space application where radiation degradation occurs in particular. A synthetic radioactive isotope of cobalt Co-60 was used with an applied dose of up to 500 kGy. These irradiation cause damage and degradation of the solar cell. A wide range of comparative characterisation methods was performed before and after irradiation. The effect of radiation on material morphology was described using electron and atomic force microscopy. Structural changes were investigated by Secondary Ion Mass Spectrometry (SIMS) with Time-of-Flight mass analysis (TOF) and Raman spectroscopy analysis. Also, the changes in noise fluctuations and current-voltage characteristics of the cell in the dark and under illumination were measured. Based on experimental measurements, the degradation was observed in the structural, optical and material cell properties as well as in electrical parameters.

Degradation analysis of GaAs solar cells at thermal stress

Abstract: The work focuses on the study of structure stability and electrical parameters of photovoltaic cells based on GaAs with Ge substrate. Solar cells of this type are used especially in adverse environments such as space applications, so their working parameters should be stable even under extreme operating conditions. Changes of electrical characteristics of the cells were recorded in the form of noise measurements for examination of distinctions in the pn-junction. Current-voltage characteristics under the light illumination and in the dark environment for comparison of the cells performance were also measured. Infrared camera showed the thermal irradiation of the stressed and damaged parts and support to localize the defected areas. Atomic force microscope (AFM) was applied for observation of changes in three-dimensional topography with high resolution. Scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) showed morphology of the solar cells and provided the elemental analysis of the samples. Raman spectroscopy provided a structural fingerprint and helped to evaluate the influence of induced degradation methods. Variations of morphology and composition were compared, detected and well-observed. Furthermore, electrical measurements proved the solar cells to be stable under temperature stresses.