We report the fabrication of densely packed InGaN/GaN nanorods with high hexagonal periodicity. Nanosphere lithography and reactive ion etching were adopted to fabricate the nanorods from planar multiple quantum wells (MQWs). Compared to the planar MQWs, the nanorods exhibit significant luminescence enhancement. This is mostly attributed to the increased radiative recombination and light extraction efficiency. Both photoluminescence and Raman measurements confirmed in-plane strain relaxation in the MQWs after nanofabrication. A reduction in strain-induced quantum confined Stark effect in the nanorods increased radiative recombination. This work is most crucial to the understanding of optical properties with respect to the carrier transport and recombination in InGaN/GaN nanorods.
The hot carrier cell aims to extract the electrical energy from photo-generated carriers before they thermalize to the band
edges. Hence it can potentially achieve a high current and a high voltage and hence very high efficiencies up to 65%
under 1 sun and 86% under maximum concentration. To slow the rate of carrier thermalisation is very challenging, but
modification of the phonon energies and the use of nanostructures are both promising ways to achieve some of the
required slowing of carrier cooling. A number of materials and structures are being investigated with these properties and
test structures are being fabricated. Initial measurements indicate slowed carrier cooling in III-Vs with large phonon
band gaps and in multiple quantum wells. It is expected that soon proof of concept of hot carrier devices will pave the
way for their development to fully functioning high efficiency solar cells.
The hot carrier cell aims to extract the electrical energy from photo-generated carriers before they thermalize to the band edges. Hence it can potentially achieve a high current and a high voltage and hence very high efficiencies up to 65% under 1 sun and 86% under maximum concentration. To slow the rate of carrier thermalisation is very challenging, but modification of the phonon energies and the use of nanostructures are both promising ways to achieve some of the required slowing of carrier cooling. A number of materials and structures are being investigated with these properties and test structures are being fabricated. Initial measurements indicate slowed carrier cooling in III-Vs with large phonon band gaps and in multiple quantum wells. It is expected that soon proof of concept of hot carrier devices will pave the way for their development to fully functioning high efficiency solar cells.
A hot carrier solar cell device that consists of heterogeneous nano-particle arrays has been proposed. It has been demonstrated that such array has good properties both as a light absorber and as a carrier conductor. The photo-generated hot carrier populations can be potentially retained due to the strong acoustic impendence between the component nano-particles, which localizes the lattice vibrational energy. The electronic and phononic properties of the nano-particles have demonstrated the potential of generating a hot carrier population. It has been demonstrated that by modulating the structure of the array, it is possible to maintain a fine electrical conductivity while strongly block the lattice heat conductivity. This helps to minimize the entropy generation during the energy conversion process, providing possibilities of realizing the high-efficiency hot carrier solar cell.
Hot carrier solar cell (HCSC) requires a slow cooling rate of carriers in the absorber, which can potentially be fullled by semiconductor superlattices. In this paper the energy relaxation time of electrons in InN InxGa1-xN superlattices are computed with Monte Carlo simulations considering the multi-stage energy loss of electrons. As a result the effect of each stage in the relaxation process is revealed for superlattice absorbers. The energy relaxation rate figures are obtained for different material systems of the absorber, i.e. for different combinations of Indium compositions and the thicknesses of well and barrier layers in the superlattices. The optimum material system for the absorber has been suggested, with the potential to realize HCSCs with high efficiency.
For silicon rich oxide (SRO) thin films prepared by sputtering deposition, we have found a trustable structure model to
describe the optical properties in the whole region of wavelength. In the process of optical characterization the
ellipsometer measures the phase change (Psi and Delta) of light reflected from the thin films, which are then fitted with appropriate structural models using Ellipsometry analysis software WVASE32. We have found that the a-Si/SiO
single-layer model can give accurate matches between calculated results and experimental results for the whole measured spectrum. The transmittance data generated from the single-layer model is consistent with the experimental results measured by spectrophotometer. Finally the model is applied to predict the optical behavior of multilayer samples, reasons are sought to explain the difference between the calculated data and the experimental data.
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