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| Master Thesis | FZJ-2017-06664 |
;
2017
Forschungszentrum
Jülich
Abstract: The InAs/GaSb core-shell nanowires (NWs) are of particular interest due to the broken gap or type III band alignment which makes them an ideal candidate for tunnelling devices. This work investigates the growth, morphological, structural and electrical characterization of InAs/GaSb NWs grown selectively by molecular beam epitaxy (MBE) on pre-patterned SiO2/Si.A first part of the thesis is devoted to substrate preparation for selective area growth of InAs NWs. The substrate preparation is a critical process in selective area MBE growth. In this thesis work, substrate preparation for selective growth of InAs nanowires is optimized. Then, our growth investigations result in the finding of suitable growth parameters of InAs and InAs/GaSb NWs grown on pre-patterned substrates. The influence of pitch (inter-wire distance) and hole diameter on the InAs NW growth is also discussed. In the case of InAs/GaSb core-shell nanowire growth, the effect of the shell growth temperature and doping of GaSb shell are examined. The morphology of InAs and InAs/GaS NWs, as well as the crystal structure of the InAs/GaSb NWs, are investigated using SEM, STEM/EDX and HR-TEM measurements. The STEM/EDX and HR-TEM measurements are accomplished by cooperation with other groups. The results show negligible dislocations at the core-shell interface indicating the almost lattice matched InAs/GaSb NW heterostructure. Also, defects like stacking faults and twinning are observed at the top of the GaSb shell.The second part of the work is focused on the InAs/GaSb nanowire device fabrication and its electrical characterization. The problems faced during selective etching of GaSb shell for contacting InAs core give an insight about the difficulty in establishing contacts for core and shell separately in InAs/GaSb radial NWs. Contacting GaSb shell is a challenging process because the GaSb shell is easily oxidizing and dissolves by reacting with metal contacts. So, careful attempts are made to contact GaSb shell with Nb/Au using those NWs for electrical characterization. The room temperature electrical characterization presents the impact of the shell doping on current-voltage characteristics in combination with the back gate voltage. The preliminary results of the electrical measurements are analyzed. The doped GaSb shell in InAs/GaSb NWs exhibited a linear (ohmic) characteristics independent of gate voltage control, while non-doped shell showed the dependency on the back gate voltage.
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