Nano-photonic structures for photodetection and thermal transfer control [electronic resource]
Keywords: Electrical Engineering.

The use of nanostructures can provide significant benefits in different optoelectronic applications. In this dissertation, the importance of nanostructures to enhance and control photodetection and radiative thermal transfer processes is investigated. This dissertation starts with overviewing the importance of surface resonances in different applications such as photodetection through hot electrons. In the first part of this dissertation, hot-electron-based metal-oxide-metal photodetector whose operation does not rely on the usual electron-hole pair generation is investigated. Despite the desirable traits of convenient fabrication and room-temperature operation at zero bias of this type of device, the low power conversion efficiency has limited its use. The benefits of reshaping one of the metallic contacts into a plasmonic stripe antenna are demonstrated. Our measurements show that surface plasmon excitations can lead to noticeable photocurrent enhancement. Moreover, these results are compared with our developed theoretical model that quantifies the spectral photocurrent in terms of the electrical and optical properties of the junction. A comparison shows that the model can predict the photocurrent accurately and can provide an explanation for the discrepancy reported previously between the measured and expected photocurrents. In the second part of this dissertation, the importance of nanostructures for near field thermal transfer control is discussed. This part begins with the investigation of the thermal transfer between finite-thickness planar slabs which support surface phonon polariton modes (SPhPs). The thickness-dependent dispersion of SPhPs in such layered materials provides a unique opportunity to manipulate and enhance the near field thermal transfer. Here, an ab-initio coupled mode theory is developed that accurately describes all of the thermal transfer properties. It is illustrated that how the coupled mode parameters can be obtained in a direct fashion from the dispersion relation of the relevant modes of the system. The work highlights and further increases the value of coupled mode theories in rapidly calculating and intuitively understanding near-field transfer. In the continuation the novel effects that periodic nanostructures can provide in near-field and far-field thermal transfer are investigated and a method that is capable of quantifying the thermal transfer between an arbitrary shaped periodic structure and a substrate is developed. By applying the method to study the thermal transfer from an array of SiC beams to a SiC substrate, the impact of the structure size and spacing on the thermal transfer is discussed. Comparisons are also made with the developed approximation methods for thermal transfer calculation such as the effective medium theory, the modified proximity and far-field approximation. By comparing their results with exact numerical calculations, the regimes of validity of these approximations are identified. Finally, based on our numerical and analytical results, the effect of the geometrical shape of nanostructures on thermal transfer is investigated and some theoretical limits for the variation of the near field thermal transfer with spacing are obtained.