Preparation Of Topological Insulator Nanostructures And Their Applications In Optoelectronic Devices

Topological insulators(TIs) represent a new type of quantum matter insulated in the bulk but conductive on the surface, which have attracted the attention from many scientists in recent years. Different from traditional semiconductor, the band structure shows that this kind of material is a typical insulator in the bulk, and it exists a bandgap near the Fermi level, but on the surfaces of topological insulators exist the Dirac type electronic that can pass through the bandgap, so its surfaces are always metallic. This particular electronic state makes TIs possess many unusual excellent performances. In addition, the one-dimensional semiconductor nanowires(NWs) and two-dimensional thin films of TIs possess unique optical and electrical properties, so TIs 1D and 2D nanostructures can be applied in optoelectronic devices. However, most researches on TIs were focused on their physical properties such as electronic states, magnetoresistive properties, etc. The application in optoelectronic device is still in the infancy. Therefore the optoelectronic device based on TIs is currently becoming one of the hottest research areas.In this thesis, we have successfully prepared high-quality single-crystal Bi2Se3 NWs and polycrystalline SnTe thin films through the thermal evaporation method and designed high performance photodetectors based on Bi2Se3 NWs /Si and SnTe films/Si heterojunction. The thesis includes the following sections:(1) Topological insulator Bi2Se3 single crystal nanowire synthesis and heterojunction photodetector. 10 nm Au, acting as catalyst for growing the Bi2Se3 nanowires, was deposited on the substrate Si. Subsequently, pure Bi2Se3 nanowires were synthesized in a single zone horizontal tube furnace via the vapor-liquid-solid mechanism. After the nanowires grew well, it would be transferred to silicon oxide. The silicon oxide was carried out by twice photolithography. The first photolithography was used for the electrode deposition, and the second was used for etching the silicon oxide on substrate through the reactive ion etching(RIE). When the nanowires had good contacts with the silicon and the gold electrode, Indium-gallium(In-Ga) alloy as another electrode was then pasted onto the back side of the Si substrate to form a good Ohmic contact to n-Si. The fabricated Bi2Se3 NWs/Si heterostructure device presented excellent performance such as high responsivity, short response time, broadband UV-NIR response and good stability. The performance of photodetector device based on Bi2Se3 NWs/Si heterostructure indicates that one-dimensional topological insulator has great potential applications in optoelectronic devices.(2) Synthesis of large area Sn Te topological insulator film and self-driven photodetector. Polycrystalline SnTe thin films with large-area and high-crystallinity were successfully prepared through thermal evaporation method in the tube furnace. By template-assisted solution etching method, SnTe film was directly grown on the Si surface, and then SnTe/Si heterostructure photodetector device was successfully prepared. The devices at the bias of 0 V and-1 V had a high on/off ratio and fast response speed, thus it could be used for self-driven photodetector. The device also had a good response performance in the UV to NIR broadband and its detectivity of 4×1012 cmHz1/2W-1 and fast response speed of 8 μs was obtained, which were the highest in the current report on topological insulator-based device. The excellent performance of such SnTe/Si heterostructure photodetector demonstrates that topological insulator has great significance in fast response and high detectivity photodetector applications.