Formation of 3D Ge quantum dots array for advanced photovolatics in layer-cake technique
Placement of quantum dots (QDs) and insight into QD's basic internal structure and optical properties lay nature cornerstones for advanced photonic devices. We report a manageable growth method for placing dense three-dimensional Ge QD arrays in a uniform or a grading size distribution, using thermal oxidation of poly-SiGe in layer-cake techniques. The QD size and spatial density in each stack could be well modulated by Ge content in poly-Si1−xGex, oxidation and underlay buffer layer conditions. Size-dependent internal structure, strain, and photoluminesce properties of Ge QDs are systematically investigated. Optimization of processing conditions was carried out for producing dense Ge QD arrays for maximizing photovoltaic efficiency.
Strained ZnSe nanostructures investigated by x-ray diffraction, atomic force microscopy, transmission electron microscopy and optical absorption and luminescence spectroscopy
Nanostructured ZnSe (Q-ZnSe) films synthesized by a wet chemical route have been studied. The evolution of particle size dependent strain, morphology and luminescence properties have been investigated, using x-ray diffraction, atomic force microscopy, transmission electron microscopy and optical absorption and luminescence spectroscopy. It is shown that the degree of structural orientation, self-organization and the nature of strain are dependent on particle size. Self-organized Q-ZnSe films with narrow particle size distribution have been successfully synthesized. Systematic particle size dependent blue shifts in the optical absorption edge and PL maxima have also been reported.
Present status of intermediate band solar cell research
The intermediate band solar cell is a theoretical concept with the potential for exceeding the performance of conventional single-gap solar cells. This novel photovoltaic converter bases its superior theoretical efficiency over single-gap solar cells by enhancing its photogenerated current, via the two-step absorption of sub-band gap photons, without reducing its output voltage. This is achieved through a material with an electrically isolated and partially filled intermediate band located within a higher forbidden gap. This material is commonly named intermediate band material. This paper centres on summarising the present status of intermediate band solar cell research. A number of attempts, which aim to implement the intermediate band concept, are being followed: the direct engineering of the intermediate band material, its implementation by means of quantum dots and the highly porous material approach. Among other sub-band gap absorbing proposals, there is a renewed interest on the impurity photovoltaic effect, the quantum well solar cells and the particularly promising proposal for the use of up- and down-converters.