Novel properties of nano-scale semiconductors based on the surface and quantum effects have been studied and applications identified. Spherical potential well model is used to study quantum effect whereas basic geometrical models are used for the surface effect. We have shown such effects to be the fundamental factors responsible for the novel nanosized semiconductor characteristics different from the bulk of same material. It is found that the surface area to volume ratio follows inverse power law. Thus at nanoscale, the surface to volume ratio increases significantly to enhance chemical reactivity. In addition, the increased surface area makes most nananocrystals highly soluble in liquid and dramatically lowers their melting temperature. The result strongly suggests also that the shape of the nanoparticles influences the surface area which has huge impact on their properties and performance. Our results of quantum size effect reveal that spatial confinement of charge carriers within semiconductor nanocrystals significantly modulates their properties such as size dependent absorption and emission spectra with non-zero discrete electronic transition energies as well as their blue shift band gaps. Thus by changing the size of the particle, we can literally fine-tune a material property of interest such as optical, electrical, and surface area. Specifically we found that InAs and InSb nano semiconductor optical absorption spectrum, in contrast to their bulk, can be tuned in broad range of UV to IR regions which are favorable operating wavelengths for nano photonic technology such as IR photo detectors and full spectrum solar cells applications.
Chemical Bath Deposition Technique has been used to fabricate thin films of copper antimony sulphide in two different growth media: water and polyvinyl alcohol and the effects of these media on the electrical and optical properties of the CuSbS 2 thin films studied. The technique required a liquid precursor; usually a solution of organic metallic powder dissolved in an organic solvent and kept in a reaction bath where reaction takes place. The precursor reaction chemicals used were copper chloride, antimony chloride and sodium thiosulphate and precipitations were on pre-cleaned borosilicate glass substrate at room temperature and pH of 9.1. Both deposits were subsequently similarly annealed for an hour each at a temperature of 250°C before testing the optical characteristics of both films using a UV-VIS-NIR 200-1100 nm range spectrophotometer and electrical characteristics, using a Quadpro four point probe. A proton induced Rutherford backscattering done on films detected thicknesses of films to be 545 nm and 514 nm for water and PVA bath deposits respectively. The thin film resistivities recorded were also 770 Ωm and 699 Ωm respectively. Absorbance, refractive indices, and other major optical parameters of the thin films varied differently with growth media in the infra red but remained fairly same in the visible and other higher frequency ranges.
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