A new dielectric Fabry-Perot cavity is considered for enhanced optical absorption in a thin semiconductor layer embedded within the resonant cavity. In this design, the front (furthest from the illuminated side) mirror is a grating structure with nearly perfect retroreflection. Proof of concept, including semianalytical calculation, and computer-aided design and simulation is performed for application in a midinfrared wavelength band based on a HgCdTe absorbing layer. The results indicate that this new type of cavity meets the combined challenges of significantly increasing the absorption efficiency and reducing the overall complexity and size of the entire device, in comparison to a conventional resonant cavity, in which both mirrors are formed from quarter-wavelength multilayer stacks.
New investigations are carried out on the optical spectral response of grating based nanophotonic structures and their
sensitivity to refractive index variations of a liquid like analyte embedded within and on top of nanometer-sized grating
structure. The phenomena examined are guided wave resonances in dielectric grating/waveguide structures,
respectively, and scatterometric effects in non-resonant structures. Both resonant and non-resonant configurations are
shown to allow refractive index detection limit on the level of 10-6 - 10-5. The spectroscopic scatterometry approach
offers also specificity in particular when the analyzed materials are dispersive and absorptive. The planarity and
operation at normal incidence as well as possibility of fabrication using silicon technologies are advantages for these
structures that permit building arrays of sensors for biochip applications.
Resonant and non-resonant phenomena in grating based photonic structures were investigated as biological and biochemical sensors particularly for water contaminants. Detectivity on the order of 10-6 RIU was found to be possible. Spectroscopic scatterometry in conical mounting at normal incidence was found to offer high sensitivity and it allows specificity in addition to refractive-index-variation measurement.
Periodic structures with minimum feature sizes in the scale of the mean radiation wavelength or less attract considerable interest due to the peculiarity of their electromagnetic (EM) response. When interference and diffraction effects become sufficiently strong, novel and interesting phenomena emerge in reflectivity, transmissivity, absorbance and even infrared thermal emission. The nanotechnology processing enables the production of high-efficiency diffraction gratings with quite small periods, down to the nanometer range, with aspect ratios higher than in spectroscopic gratings. In this paper we present the spectral measurements (transmission and thermal emission) of GaAs and silicon samples with lamella 1D gratings and mesa 2D structures. We also present the theoretical and simulation tools developed for the design and analysis of multilayer lamellar grating structures.
In this paper we present a study of infrared spectral thermal emission from varius grating structures. The structures include various lamellar grating layers of metals, silicon or GaAs on the same semiconductor substrate. The gratings have different periods, groove widths and groove depths, with feature sizes comparable to the radiated measurement wavelengths (2.5 - 25 μm). The measurement temperatures for all samples were in the range 27 to 740°K. Lateral and vertical optical confinement in the grating layers can occur. In the semiconductor grating layer in the case where the material is partially transparent lateral optical coupling exist which affect the spectral emission. In addition vertical confinement of the electromagnetic field exists which corresponds to "organ-pipe" like modes. The vertical confinement is enhanced in the case where the grating scructure is coated with metal or degenerate semiconductor. These phenomena resulted in thermal emission spectral oscillation for the wavelength range larger than the grating period.
Infrared spectral transmission, reflection and thermal emission from diffraction gratings with differing periods, groove widths and groove depths were experimentally and theoretically studied. The structural dimensions are comparable to the measured spectral wavelengths in the range 2.5 to 25 microns. For calculating the optical properties (transmission and reflection spectra), we have used an in-house S-Matrix Propagation Algorithm (SMPA) technique which is unconditionally stable versus changes in structural dimensions, optical constants and truncation order. We have experimentally studied the planar angular transmission and reflection spectrum of Si and GaAs grating samples, using FTIR spectrometry over the spectral range from 2.5 μm to 25 μm. At λ < Λ, the transmitted intensity is quasi-periodic with respect to wave number. A similar property also appears in the reflection spectra. The theoretical results for spectral transmission are in good agreement with the experimental results for the wavelength range 2.5 to 25 μm.
Theoretical work of our group is placed in the general frame of efforts to improve numerical performance and efficiency of rigorous coupled-wave analysis of grating diffraction. Mathematical transformation of Maxwell equations for a multi-layered structure to evolution equations in functional space is presented. By-construction numerically stable symbolic algorithm to solve these equations using the notion of in-layer scattering operator is proposed. On the base of this algorithm a toolbox for simulation of diffraction from multi-layered grating structures, implemented by a graphical user interface is developed. An example of simulation using this in-house software is exposed.
The infrared normal spectral emissions from degenerate (metallic-like) silicon and metallic (nickel) lamellar grating structures were investigated. The gratings were micromachined on (110) silicon wafer was with differing periods, groove widths and groove depths, where the dimensions of all samples were with feature sizes comparable to the measurement wavelengths (2.5 - 25 μm). The measurement temperatures for all samples were in the range 27 to 740 °C. Infrared normal transmission through diffraction was also measured. In general, it was found that the spectral emission of the metallic gratings was different from the degenerate silicon grating. This because the bulk absorption in the silicon samples was affecting the emission.
This paper is devoted to the analysis of the optical performance of movable-beam grating structures with both lateral and vertical displacement of the beams. We show that in the vector-diffraction domain one can design high- efficiency switches (e.g. between beam transmitter and beamsplitter mode) and modulators for polarized radiation. The devices exhibit a good tolerance to fabrication and mounting errors and a functional flexibility. In addition, by simulating the optical performance of polysilicon micro- electro-mechanical grating structures at a visible wavelength, reported in the literature, we demonstrate that our tools for rigorous electromagnetic simulation of grating structures work well in the scalar-diffraction domain.
Quantum efficiency of long-base n+p junction silicon solar cells with SiO2 layer deposited on the top cell, and with one-dimensional gratings etched in the cell's top is considered. It is assumed that the region where the useful absorption occurs is outside the grating region. The efficiency is independently optimized by adjusting the layer depth, and the grating dimensions, respectively. It is shown that optimum efficiency of the cells with grating is higher than that of the cell with SiO2 layer.
S-matrix propagation algorithm for electromagnetic analysis of multilayer gratings with Rayleigh-Fourier implementation and TM-polarization issue renewal is overviewed. Examples of polarized-antireflection grating design are considered.
A visual tool for optical properties (reflection and transmission) simulation and design of multilayer lamillar grating structures is developed, and reported in this work. The simulations are based on rigorous electromagnetic analyses using S-matrix propagation algorithms which are implemented with Fourier-transform discretization, and are coded in Matlab. Visual C++ software tools are used to feed in the input parameters and feed out the results. The input parameters include: input structure, optical and materials parameters. The tools run on a pc. Examples of some of the screen frames obtained by the tools are presented.
The scattering of plane wave incident on multilayer structure, refractive index in each layer being a function of one lateral dimension in layers plane, is considered in symbolic vector- operator form. In this framework a S-matrix propagation algorithm is developed, which rigorously eliminates backscattering from solution procedure. In the case of grating layers with unique-period refractive indices the S-matrix propagation algorithm is implemented with Fourier-transform technique of numerical solution. Stability upon increasing truncation order, layers depths and number, and a high-precision holding of power conservation test within the S-matrix propagation are found. Convergence issue for Fourier-transform implementation in TM polarization is recapitulated and a new recipe of its using is suggested. The examples of optimal designs are considered.
The effects of vacuum and (gamma) -irradiation as well as their joint effects on electrical and optical properties of phototransistors and imaging charge coupled devices are discussed. These effects will be related not only to bulk effects, but also to surface effects which are enhanced due to vacuum environments.
A S-matrix propagation algorithm for multilayer planar structure, refractive index in each layer being a function of one lateral dimension in layer's plane is developed. The algorithm is described in symbolic operator form not tied to specific representation in which boundary value problem for Maxwell equations might be solved in the layers. In the case of grating layers where refractive indices are periodic with the unique period two Fourier transform based techniques of numerical solution are implemented with S-matrix propagation algorithm. The examples of the optimal design simulations: Si grating-based zero reflection surfaces and perfect reflection layer/substrate structures are considered.
The infrared optical constants (index of refraction and extinction coefficient) and reflectance of bulk-doped n-silicon are calculated for electron concentrations up to 1021 cm-3. These calculations are based on generalized Drude-Lorentz form of dynamic dielectric function and current relaxation approach. A nonmonotonic behavior of IR absorption versus electron concentration is found. A connection between the theoretical results and available experimental data is discussed.
Semiconductor devices must face various space environments ranging from extremely low temperatures in the upper atmosphere to very high temperatures in power systems, and from low levels of ionizing radiation to high levels of neutron irradiation. Pressure varies from atmospheric pressure near the ground to vacuum at high altitudes. The semiconductor materials and devices are affected by the following external mechanisms: temperature, optical radiation, impurities and ionized gases, nuclear radiation, particle bombardment and pressure. This paper will discuss the effects of (gamma) -irradiation and pressure on optoelectronic devices such as related photodiodes, light-emitting diodes, and charge-coupled devices. These effects will be related not only to bulk effects, but also to surface effects.
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