Papers by Keyword: Amorphous Semiconductor

Abstract: The study of amorphous semiconductors is of great interest because they find important applications in many electronic devices, like large area solar cells and photosensors. We have developed a methodology for the analysis of transient response of amorphous photodiodes when switched off from steady-state and when they are exposed to a δ pulse of light. For this purpose continuity equations and the transit time effect have been calculated. For the p-i-n photodiodes, characteristics of photo current decay have been analyzed for an ideal case in which the diode is assumed to have a unit current gain. It is found that characteristics either due to decay from steady-state or due to light pulse excitation is transit time dominated. The short-circuit performance of solar cells resembles to a p-i-n diode because a solar cell is essentially a p-i-n diode which is used as an energy converter. Thus short circuit current decay of solar cells behaves similar to the photocurrent decay of the diode and the same method of analysis can be applied.

Abstract: Amorphous hydrogenated carbon thin films were deposited on Si and glassceramics substrates by reactive ion-plasma magnetron sputtering. Thin films were without (a-C:H) and with Ni nanoparticles (a-C:H:Ni). Measurement of absorption coefficient in 220-850 nm spectral range using spectrophotometer and following approximation applying of Tauc method shows that obtained a-C:H thin films material has near 3.6 eV optical band gap and confirmed that this material is amorphous semiconductor. Thin films with Ni nanoparticles have a high complex permittivity ε* and permeability μ* (ε′ ≈ 1000–10000, ε′′ ≈ 100–1500, μ′ ≈ 10–70, μ′′ ≈ 0.4-10). Some magnetic parameters of thin films were determined.

Abstract: We report on advances in the fabrication of high quality bipolar heterodiodes with oxideelectrodes. The highest rectification above 10¹⁰ is obtained for a structure from a-ZCO/ZnO/ZnO:Alon Al₂O₃ (a-ZCO: amorphous ZnCo₂O₄). Rectification better than 10⁶, a value larger than reportedfor all previous attempts, is obtained for our a-ZCO/a-ZTO (a-ZTO: amorphous zinc tin oxide), a-NiO/ZnO and CuI/ZnO diodes. The ZCO/ZnO has been used as gate in JFETs with ZnO as channel.The bipolar diodes open the field of oxide semiconductor electronics to applications in photovoltaics.

Abstract: Thin films of Sn10Sb20Se70-XTeX (0≤X≤8) composition were deposited using thermal evaporation technique. As-prepared films were amorphous as studied by X-ray diffraction. Surface morphology studies revealed that films have surface roughness ~2 nm and av. grain size ~ 30 nm. Optical band gap Eg calculated from transmittance and reflectance data showed a sharp decrease for initial substitution of Se with Te upto 2 at%. Further substitution upto 4 at%, lead to a small increase in Eg value and thereafter it marginally decreased for further substitution beyond 4at%. The trend of optical band gap variation with tellurium content has been qualitatively explained using band model given by Kastner. The dc-conductivity measurements showed thermally activated conduction with single activation energy for the measured temperature regime and followed Mayer-Neldel rule. The dc-activation energy has nearly half the value as that of optical band gap that revealed the intrinsic nature of semiconductor. The annealing below glass transition Tg led to decrease in optical band gap as well as dc-activation energy that might be related to increase of disorder in material with annealing.

Abstract: This work describes the electrical switching behavior of three telluride based amorphous chalcogenide thin film samples, Al-Te, Ge-Se-Te and Ge-Te-Si. These amorphous thin films are made using bulk glassy ingots, prepared by conventional melt quenching technique, using flash evaporation technique; while Al-Te sample has been coated in coplanar electrode geometry, Ge-Se-Te and Ge-Te-Si samples have been deposited with sandwich electrodes. It is observed that all the three samples studied, exhibit memory switching behavior in thin film form, with Ge-Te-Si sample exhibiting a faster switching characteristic. The difference seen in the switching voltages of the three samples studied has been understood on the basis of difference in device geometry and thickness. Scanning electron microscopic image of switched region of a representative Ge15Te81Si4 sample shows a structural change and formation of crystallites in the electrode region, which is responsible for making a conducting channel between the two electrodes during switching.

Abstract: A barrier-cluster model of chalcogenide glasses is employed to analyze optical transitions near the absorption edge. The influence of temperature on the optical absorption is studied. The model is used to explain the temperature shift of exponential tails of the optical absorption and the temperature dependence of the optical forbidden-band width at low temperatures.