| The research work of this doctoral thesis is mainly supported by the National Basic Research Program of China (No:2010CB327600), the National High Technology R&D Program of China (No:2009AA03Z417), National Natural Science Foundation of China (No:61020106007), New Century Excellent Talents in University (No:NCET-08-0736) and the111Program of China (No:B07005).Semiconductor nanowires (NWs) have attracted a great deal of interest in recent years due to their potential applications in electronic and optoelectronic devices. In this thesis, a great deal of work is demonstrated about experimental and theorical research on III-V group semiconductor NWs and related heterostructures NWs。GaAs NWs, InP NWs and GaAs/AlGaAs, GaAs/InGaAs, GaAs/InAsP, GaAs/InAs heterostructures NWs are grown using Au-assisted metalorganic chemical vapor deposition; InP NWs and InGaP nanoneedles are grown under self-catalyzed mechanism. A new nanowire growth model is established. The achievements are listed as follows:1. GaAs NWs are systematically researched under different growth conditions. Diameters and densities of GaAs NWs can be controlled by Au film. It is investigated that the optimum growth temperature of GaAs NWs is between440℃and500℃. At this growth temperature, GaAs NWs are pure zincblende (ZB) without any defects. The alloy droplet acts as a catalyst rather than an adatom collector during NWs growth. With the supersaturation of droplets increasing, NWs growth rate decrease. Different type substrates affect on the densities of NWs.2. Stacking-faults-free ZB GaAs NWs are realized using GaAs/AlGaAs buffer layers via a two-step growth on Si substrate. The buffer layers are optimized. It can be concluded that the GaAs/AlGaAs buffer layers block the diffusion of Au atom to Si substrate and Si atom from substrate to NW.3. P-doped and n-doped GaAs NWs are grown. The effect of flux rates of DEZn on NWs’morphology is very large. The cause of NWs bending at high V/III is explained. The effect of flux rates of SiH4on NWs’morphology is small. The electrode is fabricated on n-doped GaAs NWs grown on p-type GaAs substrate. From the test results, it is revealed that the contact between electrode and NW is good.4. Vertical InP NWs are grown at different temperature. The effect of In diffusion adatom on InP NWs growth increase with growth temperature. The structure of NWs is ZB/WZ (wurtzite) mixture. The peek of PL of InP NWs can be changed by tuning growth temperaute.5. Self-catalyzed InP NWs are grown on InP substrate at different temperature and V/III. The NWs can be optimized according to the results. Simultaneity, catalyst free InGaP nanoneedles grown on Si substrate are researched. These nanoneedles can also be optimized by tuning pre-growth flux time and rate of In atom, growth temperature and V/III.6. GaAs/AlGaAs axial and radial heterostructure nanowires are deeply researched. After GaAs NWs growth, axial and radial heterostructure can be realized by tuning growth temperature. Axial heterostructure can be achieved at low temperature, while radial heterostructure at high temperature. Because GaAs and AlGaAs have almost the same lattice constant, the grown NWs are pure ZB structure.7. GaAs/InGaAs and GaAs/InAsP radial heterostructure nanowires are grown. With temperature increasing, the sidewalls of GaAs/InGaAs NW are changed from{112} into{110}.8. Due to the interface energy restriction between GaAs and InAs, it is difficult that InAs NW is directly grown on axial GaAs NW. InxGa1-xAs buffer inserts, which can release the strain and realize GaAs/InAs axial growth, are grown between GaAs and InAs. Critical diameter changed with buffer inserts is calculated using standard elastic theory. A novel nanowire growth model is established, control of the crystal structure of InAs NWs by tuning contributions of In adatom diffusion. |
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