In this letter, we report on the fabrication of nearultraviolet photodetectors based on gallium nitride (GaN) layers grown on a Si(111) substrate. Optoelectronic characterization was performed using front-side and backside illumination, the latter possible by locally etching the Si substrate under the detectors using reactive ion etching. The dark current after removal of the Si substrate decreased by two orders of magnitude to around 20 fA at −1 V for a 300-μm-diameter Schottky photodiode. Responsivity at the cutoff wavelength (370 nm) was equal to 35 mA/W for the backside illumination. Detection at smaller wavelengths was not possible due to a nonoptimized layer stack. These first results do however illustrate the potential of backside-illuminated GaN-on-Si Schottky photodiodes in 2-D UV imagers.Index Terms-AlGaN, backside illumination, extreme ultraviolet (EUV), Schottky photodiode, ultraviolet imaging.
With the continuous search for alternative treatment for End Stage Renal Disease (ESRD), the use of synthetic scaffolds as a prospect is becoming a forefront in regenerative medicine. This study aimed to fabricate and evaluate the effects of varying electrospinning parameters (the applied voltage, spinning distance and flowrate) to the fiber diameter and pore size of the scaffolds produced using polyvinylidene fluoride (PVDF). Electrospun scaffolds were subjected to scanning electron microscopy (SEM) and strain apparatus to assess structural and tensile properties. Results showed that applied voltage, spinning distance, and flowrate directly affect the overall pore size and fiber diameter of the electrospun scaffolds, as well as resulting in a direct effect to the tensile strength of the electrospun scaffold. The optimal values for the parameters in fabricating a PVDF electrospun scaffold would be a voltage of 20kV, a spinning distance of 100mm and a flowrate of 0.5ml/h. Results also show that spinning distance and flowrate have statistically more impact on the outcome of the fiber diameters, while applied voltage and spinning have statistically more impact on the outcome of the pore sizes. Moreover, the electrospun scaffolds acquired thinner fiber diameters and smaller pores sizes when compared to that of the native kidney tissue. Nonetheless, the promising mechanical integrity of the electrospun PVDF-based scaffolds offer a potential approach to addressing ESRD.
Luminescent concentrators may have significant promise for producing low-cost PV energy. Luminescent concentrators convert the solar spectrum and concentrate the sunlight, but the benefit that can be obtained by the spectral conversion is not obvious. This paper presents the results of a theoretical study of the impact of spectral concentration. A well-known set of relationships for PV cell efficiency was modified to include the effect of the variation in internal quantum efficiency for different wavelengths, and then used to examine the impact of spectral concentration for materials with different bandgaps.The results suggest that spectral concentration leads to only a modest increase in PV conversion efficiency.
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