Dependence Of Spectral Response Research Articles

Design and Analyses of Broadband Perfect Light Absorber for Visible and Near IR Frequencies using Plasmonic Metamaterials

Metal-insulator-metal nanostructures based plasmonic metamaterials have been extensively explored for the design of broadband perfect light absorption in all the technologically relevant windows of electromagnetic spectrum. We have computationally studied a unique metal-insulator-metal nanostructure for the design of a broadband perfect light absorber in the visible and near infrared frequencies. We explored different metal combinations for the same metal-insulator-metal geometry for the absorber design. The study shows that the dependence of spectral response is dominated by the geometrical shape and arrangement, rather than the nature of the metal combinations. We report an average light absorption of more than 80% from 400nm to 1100nm wavelength range.

Ultra-long-range symmetric plasmonic waveguide for high-density and compact photonic devices

This study reports a symmetric hybrid plasmonic waveguide consisting of a cylindrical metal nanowire surrounded by low-index SiO₂ and high-index Si covered with SiO₂. The symmetric circumambience relative to the metal nanowire significantly facilitates the present design to minimize the energy attenuation resulting from Ohmic losses while retaining highly confined modes guided in the low-index nanoscale gaps between the metal nanowire and the high-index Si. The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail, showing long propagation lengths beyond 10 mm with normalized mode areas on the order of 10⁻². In addition to enabling the building of long-range plasmonic circuit interconnects, the compactness and high-density integration of the proposed structure are examined by analyzing crosstalk in a directional coupler composed of two such waveguides and bending losses for a 90° bend. A relatively short coupling length of 1.16 μm is obtained at a center-to-center separation of 0.26 μm between adjacent waveguides. Increasing the separation to 1.65 μm could completely prevent coupling between waveguides. Power transmission exceeds 80% in the case of a 90° bend with small radius of curvature of 0.5 μm. Moreover, the dependence of spectral response on coupling length and the transmission of a 90° bend, ranging from telecom wavelengths of 1.40 to 1.65 μm, are investigated. Over a wide wavelength range, a strong coupling length dependence on wavelength and a high transmission for a 90° bend also make the proposed plasmonic waveguide promising for the realization of wavelength-selective components.

Large area single and stacked p-i-n photodiodes as a color image sensors

AbstractSingle and stacked p-i-n sensing elements for image recognition and color extraction applications are presented. The aim of this work is to optimize the performance of the a-SiC:H thin films layers in order to enhance its performance when making part of the structure of large area image and color sensors. The efforts are focused mainly on doped n- and p-type layers at high and low doping levels with and without carbon. The structural and optoelectronic properties of the single layers were determined through infrared and visible spectroscopy, temperature-dependent conductivity, and were complemented by CPM measurements. Junction properties, carrier transport, photogeneration and collection efficiency are investigated from dark and illuminated current-voltage characteristics and spectral response measurements, with and without additional background illumination and under different light bias conditions. The spectral response dependence on the applied voltage and on optical bias was also studied. Results show that the spectral sensitivity is strongly dependent on the applied voltage, namely the maximum spectral sensitivity shifts with the voltage, and at certain wavelengths the spectral response goes down to zero, which allows a different selectivity, and enables color recognition.

On the electrical conductivity in porous silicon under light and electron beams

The `photoconductive' properties of a porous silicon layer (∼10 μm thick) formed by anodization of p-type silicon wafer having aluminum ohmic contacts is studied. The porous silicon layer has a high dark resistivity, (>100 Ω m), a photoconductivity in visible light and for electron beams of 50–100 keV; a dependence of spectral response on bias voltage is also observed. These properties are interpreted as the result of an increase in the band gap in porous silicon correlated with the layer morphology and the formation of a heterojunction whose field separates generated pairs.