Isakov, I; (2015) Semiconductor nanowires grown by molecular beam epitaxy for electronics applications. Doctoral thesis , UCL (University College London).

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Abstract

One-dimensional nanostructures such as semiconductor nanowires are very attractive for application in next generation electronics. This work presents an experimental study of InAs-based and ZnO-based nanowires grown by molecular beam epitaxy for electronics applications. InAs, InAsP and InAsSb nanowires were grown self-catalytically on silicon. Phosphorus incorporation was studied by means of HRTEM, XRD, EDX and PL. The phosphorus incorporation rate was shown to be 10 times smaller than that of arsenic. InAs and InAsP nanowires exhibit the wurtzite structure with a high density of stacking faults and phase boundaries. Conversely, InAsSb nanowires exhibit the zincblende structure with the density of stacking faults decreasing as the antimony content increases. Antimony incorporation and reduction of the stacking fault density improves the nanowire mobility. ZnO and ZnMgO nanowires and ZnO/ZnMgO core-shell nanowire heterostructures were grown by plasma-assisted molecular beam epitaxy on various substrates with gold particles as a growth catalyst. Nanowire growth was shown to occur only at temperatures between 700 and 850 C and Zn pressures between 1 and 3 10 7 Torr. A two-step growth procedure on silicon was implemented to increase the yield of nanowire growth. Mg incorporation was shown to be 4 times smaller than that of Zn. At Mg content higher than 20 %, MgZnO rocksalt phase segregation is observed in the as-grown samples. Core-shell nanowires were fabricated by growing the shell at a lower temperature of 500 C. ZnO nanowire field effect transistors were fabricated and optimised. High- and low-temperature transport measurements allowed determination of the bulk nanowire and contact properties. Nanowires grown on sapphire and silicon were compared. Nanowires grown on sapphire exhibit an extra donor that determines their low temperature conductivity and give a wider photoluminescence band-edge emission peak. A novel technique to measure the spectrum of deep traps in nanowire field effect transistors was implemented to study ZnO nanowires.

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