Growth And Properties Of â…¢-â…¤ Narrow Bandgap Semiconductor Nanowire And Their Heterostructures

III-V narrow bandgap semiconductor nanowires(NWs) possess several unique features, such as small bandgap, high carrier mobility and small effective mass. The unique features makes III-V narrow bandgap NWs not only suitable for the research of fundamental physical phenomena like probing Majorana fermion, but also useful in the application of future nanoscale optoelectronic device, infrared detection, gas sensing and spintronics, etc. Therefore, III-V narrow bandgap NWs have emerged as a hot topic in recent years. In this thesis, we carried out the synthesis of III-V narrow bandgap NWs by Au-assisted molecular beam epitaxy(MBE), and characterized their morphology, crystal structure, as well as chemical composition in details, by means of scanning electron microscopy, transmission electron microscopy, and X-ray enengy dispersive spectroscopy. Meanwhile, a preliminary study on the Raman scattering and electrical properties has also been accomplished.We have investigated the influence of growth temperature on the morphology and crystal structure of In As NWs, determined the optimal growth temperature range of In As NWs, and highly oriented, uniform, and defect-free In As NWs with wurtzite(WZ) structure have been grown at last. Meanwhile, we have also investigated the effect of substrate orientation on In As NW growth, finding that the <111>B direction always dominates despite of the variation of substrate orientations. Raman scattering results demonstrate the uniformity and WZ structure of In As NWs, while the high Ion/Ioff ratio of In As NW back-gated field effect transistor implies the good electrical properties of the as-grown In As NWs by MBE.Through the introduction of Bi ambient into the normal growth process of In As NWs, we have successfully realized the phase control of In As NWs. In As NWs can change abruptly from WZ phase to zinc blende(ZB) structure once Bi shutter is opened, and the structure of In As NWs will return back to WZ phase again through a gradual structure evolution after the close of Bi shutter. However, with the increase of Bi flux, the proportion of ZB phase will also increase. In this regard, a stable ZB phase of In As NWs can be finally formed if a high Bi flux is introduced in the NW growth. The underlying tuning mechanism of Bi ambient for the crystal structure of In As NWs lies in the strong surfactant effect of Bi element, which can modify the diffusion process of adsorbed In atoms on the substrate, thus affecting the structure formation of In As NWs.We have also synthesized In As/In As Bi heterostructured “nanotrees” via sequential vapor-liquid-solid(VLS) growth mechanism. In As “nanotrunk” growth is dominiated by Au-catalyzed VLS mode, while In As Bi “nanobranch” is grown under Bi-assisted VLS mode. When a very high Bi flux has been introduced into the growth process of In As NWs, Bi droplets formed on the sidewalls of the already-grown In As NWs, and In As Bi nanobranches will grow on the sidewalls via VLS mechanism catalyzed by Bi droplets. In this study, we find that Bi element can act as catalyst and dopant simultaneously.The MBE growth of In As/In Sb nanowire heterostructures has also been conducted. It is found that, with the change of growth temperature and V/III BEP ratio, the growth mode of In Sb can varies between VLS mechanism and vapor-solid(VS) mechanism, and then both In As/In Sb axial NW heterostructures and core-shell NWs were grown in our study. In the axial NW heterostructures, In As and In Sb possess a WZ and ZB crystal structure, respectively, and no planar defects are found in both In As and In Sb sections. At the same time, the In As-In Sb heterostructured interface is very sharp, and the WZ-ZB structural transition is accomplished in the distance of only one or two atomic layers, implying that high quality In As/In Sb axial NW heterostructures have been obtained.As the last part, a detailed investigation of MBE-grown Ga As/Ga Sb nanowire heterostructures and related growth mechanism is given. It is found that the growth temperature range of Ga Sb NWs is very narrow, and Ga Sb has a strong tendency to grow epitaxially on the sidewalls of Ga As NWs, thus forming Ga As/Ga Sb core-shell NWs. Meanwhile, a bulgy Ga Sb nanoplate often resides on the top of Ga As/Ga Sb core-shell NWs. Transmission electron spectroscopy analyses imply that, both Ga As core and Ga Sb shell NWs have a WZ structure with planar defects, but Ga Sb nanoplate possesses a defect-free ZB structure. To our knowledge, this is the first report of WZ-structured Ga As/Ga Sb core-shell NWs. In light of the the special advantages of core-shell NW heterostructures, this study will contributes much to the further development of narrow bandgap semiconductor core-shell NW structures.