Pseudo-potential calculations of the electronic and optical properties of GaxAlyIn1–x–yAs
A method for calculating the electronic structure of the quaternary alloy GaAlInAs is presented with zinc blende structure. We have used the empirical pseudo-potential method coupled with the virtual crystal approximation (VCA). The electronic structures are studied for GaAlInAs (x = 0.24, y = 0.24) and GaAlInAs lattice matched to InP as well GaAs. In addition a method for calculating the refractive index is presented, which we used the Sellmeir model. The composition dependence of the refractive index is discussed, the results indicate that refractive index decrease with alloying composition of the quaternary alloy GaAlInAs lattice matched to InP and GaAs.
Design optimization of InGaAsP-InGaAlAs 1.55 /spl mu/m strain-compensated MQW lasers for direct modulation applications
A comprehensive simulation study of InGaAsP (well)/InGaAlAs(barrier) 1.55 /spl mu/m strain-compensated MQW lasers is presented. For MQWs, a uniform vertical distribution of holes is achieved due to a reduced effective hole confinement energy by optimizing the bandgap and strain of the barriers and p-doping in the active region. Some preliminary results are also presented for the manufactured lasers using these QWs indicating a good material platform.
Measuring Sheet Resistances of Dielectrics Using Co‐Planar Hydrogel Electrochemical Cells with Practical Applications to Characterize the Protective Quality of Paints on Sculptures
Electrical properties of thin dielectric films at the solid-liquid phase boundary are an important performance characteristic of many devices, coatings and sensors. In this paper, co-polymeric hydrogels of polyacrylic acid co-sulfonic acid, swollen with a salt solution to act as the solid electrolyte, were used to assess interfaces using electrochemical impedance spectroscopy (EIS) in a co-planar geometry. Silane-modified glasses were characterized by the co-planar hydrogel EIS cell and found to be distinguishable based on their surface monolayer chemistry. EIS measurements were also made on primed and painted metal substrates, using both test panels and an outdoor sculpture, Tony Smith's Stinger. The panels were then exposed to accelerated and outdoor weathering and showed degradation on the surface paint layers, which was observable electrochemically using EIS and confirmed visually by SEM. Electrochemical spectral features were compared between data from a standard paint-test cell versus this co-planar hydrogel cell; both cell types were able to measure coating capacitance, providing useful information about the condition of the bulk coating. Yet, sheet resistance (Rs) was a spectral feature seen only by the co-planar hydrogel cell. Thus, it can be concluded that the use of such co-planar hydrogel cells can provide an earlier warning sign to coating degradation and such cells provide a new type of spectral information that is not assessable by the standard geometry.