KEYWORDS: Indium gallium phosphide, Zinc, Particles, Radioisotopes, Ionization, Solar cells, Photons, Solar energy, Chemical species, Energy conversion efficiency
In this work, a hybrid structure is designed that combines both alpha-photovoltaic (APV) and alpha-voltaic (AV) effect. A ZnS phosphor generates photons when exposed to alpha particles. The photons are captured and converted to electronhole pairs (EHP) in an underlying layer of InGaP PV (APV). Some of the alpha particles propagate to the InGaP directly producing EHP in InGaP (AV). Numerical simulations using SRIM compared the power output in the InGaP PV through a parametric study of phosphor thickness. The ionization energy deposited in the ZnS layer was compared to the ionization energy in the InGaP. The ZnS phosphor thickness was varied to maximize electrical power output. The ZnS phosphor also performs the function of slowing down alpha particles so those alphas that penetrate to the InGaP are less energetic and damage is reduced to the InGaP PV. Initial measurements were performed using current-voltage (IV) curves during exposure to alpha particles from a National Electrostatics Pelletron ion accelerator. The energy deposited into the phosphor and PV materials is calculated from SRIM simulations. Simulation results optimizing phosphor thickness in this hybrid APV and AV structure generates 4.3% efficient energy conversion for radioisotope battery application producing greater than 500 μW(electrical) can be generated per 100mCi of 241Am
The application of photonic crystals in biosensor applications has lead to the development of highly sensitive and
selective sensor elements. The research efforts undertaken by this group have led to the development of a photonic
crystal transducer that acts as a waveguide, nanofluidic flow channel, and resonant defect cavity. This sensor architecture shows promise for greatly enhancing the emission of naturally fluorescent or fluorescently-labeled biomolecules. Due to its transparency in the visible regime, GaN is a viable candidate for this photonic crystal biosensor application. This paper provides an overview of the sensor architecture as well as a discussion of one particular bottom-up approach to its fabrication. Molecular Beam Epitaxy (MBE) growth of heavily Mg doped GaN can result in inversion of the surface polarity from Ga-polar to N-polar GaN. This bottom-up approach includes patterning and etching of the Mg inversion layer, followed by
re-growth of the opposite polarity to produce periodically poled GaN. Subsequent wet etching of N-polar regions then produces a GaN based photonic crystal structure. This process shows promise for achieving high aspect ratio, highly anisotropic nanostructures.
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