One-dimentional Semiconductor Nanostructure Composition Modulation And Its Applications In Nano-information Devices

One-dimentional semiconductor nanostructures represent the most fundamentalbuilding blocks for integrated all-semiconductor electronic devices and circuits. Theunique physical and chemical properties of nanostructures have promisingapplications in novel nanoelectronic and nanophotonic devices and system, whichattracted extensive interest of the scientific community and academia. Bandgap is oneof the most important parameters for semiconductor-based properties among these keydeterminants. Bandgap decides the absorption and emission properties of thesemiconductor fundamentally. However, the nature semiconductor type is so limitedthat bring many inconvenience to the available application of photoelectric devices. Inorder to address this limitation in nature semiconductors, the researchers havedeveloped bandgap modulation. These system modulation based on thesemiconductors has provided a broad space for enriching bandgaps in nanometer scaleand new research work. Additionally, the continuous graded bandgap was realized byintegration of different semiconductor matericals along the single substrate or evenalong a single-nanostructure, which take an important step for the application of largescale integrated device. Considering about the importance status of the nanoscalebandgap modulation along the single-nanostructure, it needs further investication tostudy the bandgaps diversification in the excellent performance of nano-informationdevices.In this work, traditional synthetic strategy was used to realize one-dimetionalnanostructures with various special bandgap through chemical vapor depositionmethod. We have summarized our new achievements in changing thebandgap/composition of semiconductor gradually or abruptly along the length/widthdirection of single nanostructures. Meanwhile, using these special nanostructures,several kinds of nano-information devices were successfully constructed and systemtested. The main achievements are summarized as follows:(1) We succeeded in exchange of solid-state source at high temperature duringthe growth assistant by a step motor integrating pulling system into traditionalchemical vapor deposition strategy. Based on these improved-strategy, we firstlydesigned and realized symmetrical composition graded CdSxSe1-x(x=0~1) nanowires(NWs) along axial direction. This nature one-dimensional cavity was acted as a high-quality nanoscale lasers by constructing a symmetrical composition distributionalong the wire length. More importantly, this unique “wide-narrow-wide” bandgapmodulation of single-nanowire was achieved. Photoluminescence measurments showthat the emission color of these NWs gradually varied from the red at the centralregion to the green at the both ends along the length. The symmetrical wire canefficiently avoid the self-absorption induced energy loss for the excited light at itscentral region and work as a high efficiency passive waveguide cavity. We havefurther demonstrated that the optically pumping lasing threshold in thesesymmetrically composition-graded NWs is much lower compared with that ofcomposition-homogeneous NWs. This is the first report about reducing the thresholdof lasers by avoiding the self-absorption induced energy loss.(2) We developed an in-situ temperature controlled CVD method to realize thegrowth of high-quality interfacially sharp axial nanowire heterostructures (NWHs). Asan example, CdS/CdSxSe1-xaxial NWHs with single or double junctions wereachieved using this growth strategy, which overcome the difficulties that solid powdersource is difficult to control in the body cavity. Microstructure characterizationsdemonstrated that these NWHs have single-crystalline structure with interfaciallysharp interfaces at the junctions. Local photoluminescence results showed twoseparate bandedge emission bands at the junctions, coming from the adjacent twodifferent semiconductors, respectively. The NWHs can efficiently avoid theself-absorption induced energy loss for the excited light at its central region and workas a total passive waveguide cavity. The energy loss in these NWHs is much lowercompared with that of composition-homogeneous NWs and compositionsymmetrically graded nanowires. Optically pumped high-quality NW lasing isdemonstrated at room temperature based on these unique NWHs.(3) We have synthesized high-quality CdS0.49Se0.51/CdS0.91Se0.09nanoribbonlateral heterostructures through an in-situ source changing CVD route. The achievedstructures are composed of nanoribbons with two different semiconductor alloysepitaxially grown side by side at the lateral direction with sharp interfaces, whichrealize the abrupt bangdgap variation. Under a UV laser illumination, it shows thatthese nanoribbons have a fine sandwich-like structure, with red at both lateral sidesand green at the central region. Using these unique lateral structures,high-performance visible-light photodetectors are achieved based on singlenanoribbon lateral heterostructures. The devices have broad spectral response (FWHMof160nm), high responsivity (1.16×103A/W), high Ion/Ioffratio (106) and high quantum efficiency (106), with these charateristics all superior to those of devicesbased on single composition semiconductor nanostructures.(4) We have successfully synthesized semiconductor/dielectric/metalnanostructure (CdS-SiO2-Au) by a multi-step route and studied the infuence of surfaceplasmons on the band-edge emission of CdS NWs. Systematic study of the opticalperformance revealed that the band-edge emission of CdS nanowires in this novelstructure is enhanced5fold by the surface plasmon resonance. Time-resolved PLmeasurements were performed to further confirm the above discussed enhancementmechanism. Meanwhile, the optimum distance (thickness of SiO2layer) between thegold nano-particles and CdS NWs for the PL enhancement is found to be about5nm.These interesting CdS-SiO2-Au NWs have potential applications in photocatalysis,photodetectors and bio-nanotechnology.