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Towards highly-doped Ge and ZnO nanowires: Growth, characterization and doping level analysis
Pejchal, Tomáš ; Mikulík,, Petr (oponent) ; Grym,, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Highly-doped semiconductor nanowires represent a promising class of nanostructures with prospective applications in electronics, optoelectronics or bio-sensing. This thesis is focused on the growth and in-depth characterization of germanium and zinc oxide nanowires, with the aim of acquiring high doping levels. The first part of the thesis deals with the growth of germanium nanowires via the vapour–liquid–solid (VLS) process. Several factors impacting the nanowire growth and morphology are described – the composition of the catalytic particle, the role of surface adsorbates and the incorporation of atoms from the catalyst into the nanowire. The nanowires are grown from gold nanoparticles either in ultra-high vacuum (the MBE-like process) or in the presence of atomic-hydrogen vapour (mimicking the CVD process), resulting in dissimilar nanowire morphology and growth direction. The combined effect of atomic hydrogen adsorption and gold catalyst spreading is revealed – being the key element explaining the difference in nanowire morphology when MBE and CVD growth techniques are utilised. Further, the Ge nanowire growth from group-III-containing catalysts is studied, with the intention of doping the nanowires via the incorporation of atoms from the catalyst droplet. The in-situ prepared alloyed Au–Ga catalyst is found to be applicable for germanium out-of-plane nanowire growth – although the catalyst stability is lower than for pure Au. Despite a high dopant concentration in the catalyst, no gallium incorporation into the nanowire is observed. Hence, this method of nanowire doping is proved unsuitable for the material system selected. The third part of the thesis covers the characterization of ZnO nanowires and the development of a protocol for their diffusional doping with gallium. The impact of nanowire annealing on the concentration of oxygen vacancies (VO) is demonstrated – annealing in H2O2 gas decreases the VO concentration, compared with annealing in high vacuum. Further, Ga incorporation into ZnO nanowires is documented with in-situ SEM when annealed above 350 °C. Moreover, gallium-induced decomposition of ZnO nanowires is observed above 450 °C. The concentration and spatial distribution of Ga within the nanowires is assessed using STEM EDS and a theoretical model for Ga diffusion. The correlation between the VO concentration and the Ga incorporation into ZnO is found. Gallium concentration in the order of 10^21 cm^-3 is reached in the nanowires – demonstrating the suitability of the presented diffusional-doping method for achieving high Ga doping levels needed for prospective bio-sensing applications in the IR region.
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Morfologie ostrůvků germania v přítomnosti gallia a zlata
Pejchal, Tomáš ; Čechal, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Tato práce se zabývá morfologií ostrůvků germania v přítomnosti zlata, stříbra a gallia, připravených na povrchu Ge(111) pomocí napařování za podmínek UHV. V práci je představena rešerše povrchových rekonstrukcí uvedených kovů na povrchu Ge(111). Je ukázáno, že koncentrace, velikost i tvar ostrůvků závisí na přítomnosti jednotlivých kovů i teplotě depozice. Povrchová struktura a morfologie vzorků byly studovány metodami RHEED a SEM.
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Modifikace růstu polovodičových nanovláken
Pejchal, Tomáš ; Grym, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Tato diplomová práce se zabývá růstem polovodičových nanovláken na substrátu Ge(111). Nanovlákna byla připravena metodou PVD (physical vapor deposition), jejich růst byl katalyzován Au koloidními nanočásticemi. V práci je popsán vliv změny depozičních podmínek na výslednou morfologii nanovláken. Je ukázáno, že preferenčním směrem růstu Ge nanovláken je směr . Byla pozorována i Ge vlákna orientace .
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Towards highly-doped Ge and ZnO nanowires: Growth, characterization and doping level analysis
Pejchal, Tomáš ; Mikulík,, Petr (oponent) ; Grym,, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Highly-doped semiconductor nanowires represent a promising class of nanostructures with prospective applications in electronics, optoelectronics or bio-sensing. This thesis is focused on the growth and in-depth characterization of germanium and zinc oxide nanowires, with the aim of acquiring high doping levels. The first part of the thesis deals with the growth of germanium nanowires via the vapour–liquid–solid (VLS) process. Several factors impacting the nanowire growth and morphology are described – the composition of the catalytic particle, the role of surface adsorbates and the incorporation of atoms from the catalyst into the nanowire. The nanowires are grown from gold nanoparticles either in ultra-high vacuum (the MBE-like process) or in the presence of atomic-hydrogen vapour (mimicking the CVD process), resulting in dissimilar nanowire morphology and growth direction. The combined effect of atomic hydrogen adsorption and gold catalyst spreading is revealed – being the key element explaining the difference in nanowire morphology when MBE and CVD growth techniques are utilised. Further, the Ge nanowire growth from group-III-containing catalysts is studied, with the intention of doping the nanowires via the incorporation of atoms from the catalyst droplet. The in-situ prepared alloyed Au–Ga catalyst is found to be applicable for germanium out-of-plane nanowire growth – although the catalyst stability is lower than for pure Au. Despite a high dopant concentration in the catalyst, no gallium incorporation into the nanowire is observed. Hence, this method of nanowire doping is proved unsuitable for the material system selected. The third part of the thesis covers the characterization of ZnO nanowires and the development of a protocol for their diffusional doping with gallium. The impact of nanowire annealing on the concentration of oxygen vacancies (VO) is demonstrated – annealing in H2O2 gas decreases the VO concentration, compared with annealing in high vacuum. Further, Ga incorporation into ZnO nanowires is documented with in-situ SEM when annealed above 350 °C. Moreover, gallium-induced decomposition of ZnO nanowires is observed above 450 °C. The concentration and spatial distribution of Ga within the nanowires is assessed using STEM EDS and a theoretical model for Ga diffusion. The correlation between the VO concentration and the Ga incorporation into ZnO is found. Gallium concentration in the order of 10^21 cm^-3 is reached in the nanowires – demonstrating the suitability of the presented diffusional-doping method for achieving high Ga doping levels needed for prospective bio-sensing applications in the IR region.
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Modifikace růstu polovodičových nanovláken
Pejchal, Tomáš ; Grym, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Tato diplomová práce se zabývá růstem polovodičových nanovláken na substrátu Ge(111). Nanovlákna byla připravena metodou PVD (physical vapor deposition), jejich růst byl katalyzován Au koloidními nanočásticemi. V práci je popsán vliv změny depozičních podmínek na výslednou morfologii nanovláken. Je ukázáno, že preferenčním směrem růstu Ge nanovláken je směr . Byla pozorována i Ge vlákna orientace .
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Morfologie ostrůvků germania v přítomnosti gallia a zlata
Pejchal, Tomáš ; Čechal, Jan (oponent) ; Kolíbal, Miroslav (vedoucí práce)
Tato práce se zabývá morfologií ostrůvků germania v přítomnosti zlata, stříbra a gallia, připravených na povrchu Ge(111) pomocí napařování za podmínek UHV. V práci je představena rešerše povrchových rekonstrukcí uvedených kovů na povrchu Ge(111). Je ukázáno, že koncentrace, velikost i tvar ostrůvků závisí na přítomnosti jednotlivých kovů i teplotě depozice. Povrchová struktura a morfologie vzorků byly studovány metodami RHEED a SEM.
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