Contronllable Doping Of Chalcogenides One-dimensional Nanostructrues And Their Nano-electronic And Optoelectronic Applications

Chalcogenides compound semiconductors are main direct-gap semiconductors, their one-dimensional (1D) nanostructures, such as nanowires (NWs), nanoribbons (NRs), nanotubes (NTs) are promising nanomaterials for nano-electronic and nano-optoelectronic devices, owing to the unique optical and electrical properties. In past few decades, tremendous efforts have been devoted to exploiting the potential applications of semiconductor nano-structures in new-generation nanoelectronic and nano-optoelectronic devices. However, the uniform geometry and performance of is hard to achieve and the n-type doping and p-type doping are uncontrollable, which limit the applications in nano-electronic and nano-optoelectronic devices of these nanomaterials. Therefore, developing a method, by which1D nanostructures can be synthesized with contronllable doping, uniform morphologies and performances, exploring applications of these nanostructures in nanoelectronic and nano-optoelectronic devices, and optimizing the structures of devices to obtain high-performance nanodevices have great significance.To cure the above problems, this dissertation started with synthesis of high-crystallinity chalcogenides compound semiconductors1D nanostructures with n-type and p-type doping, uniform morphologies and contronllable performances. The applications of Ⅱ-Ⅵ group semiconductors1D nanostructures in nanoelectronic and nano-optoelectronic devices were explored, and a series of nano-devices, such as field-effect transisitors (FETs), light-emmitting diodes (LEDs), photovoltaic (PV) devices, photodetectors (PDs), nonvolatile memory were fabricated. The main reseach results obtained as follows:1. Chalcogenides compound semiconductors1D nanosturctures with uniform geometry were synthesized and efficient doping via thermal evaporation method and chemical vapor deposition method, including Ga-doping CdS NRs, Ga-doping CdSe NRs/NWs, Sb-doping ZnTe NRs and N-doping ZnSe NRs. Ga-doping CdS NRs have a single-crystal wurtzite structure with a growth orientation of [001]; Ga-doping CdSe NWs and NRs have single-crystal wurtzite structure with growth orientation of [001]; Sb-doping ZnTe NRs have a single-crystal zinc blende structure with a growth orientation of [11-1]; N-doping ZnSe NRs have a single-crystal zinc blende structure with a growth orientation of [-1-11]. The n-type and p-type conductivity of1D nanostructures were confirned by constructing nano-FETs.2. High-performance nano-FETs based on individual NRs were constructed by using high-κ HfO2dielectric and top-gate geometry,(ⅰ) The transconductance, carrier mobility, subthreshold swing, current On/Off ratio and threshold voltage of n-type CdS:Ga NR top-gate MISFET were233nS,81cm2/Vs,0.59V/dec,～106,～1.8V, respectively. Comparison with MOSFET, these value were enhanced by10,4,>67,～106and>10times,(ⅱ) The transconductance, carrier mobility, subthreshold swing, current On/Off ratio and threshold voltage of p-type ZnTe:Sb NR top-gate MISFET were372nS,11.2cm2/Vs,1.58V/dec,7×102,-1V, respectively. Comparisons with MOSFET, these values were enhanced by40,10,186,4M02and29times.3. A simple method for fabricating ID nanosturctures/Si heterojunctions was developed. Photolithography and subsequently wet-etching were performed to define insulating pads on the Si substrate. Then the as-synthesized NWs/NRs were transferred onto the substrate. After dispersion, some NWs/NRs would cross on the edges of the insulating pads and partially contact with the underlying Si substrate; heterojunctions were then formed in the contact regions. By using this simple method, LED, PV device and PDs can be achieved on one device. N-CdS/p-Si and n-CdSe/p-Si nano-LEDs were fabricated, which show excellent rectification characteristic with rectification ratio up to104. At forward bias, bright light spots with yellow and red color are observed from LEDs. From the room temperature electroluminescence (EL) spectrum of the LEDs, intense emission peaks located at524nm and710nm are investigated, which are consistent with the band-edge emission of CdS and CdSe, indicating that the emission mainly come from the side of the CdS and CdSe NR. This result is reasonable since the radiative recombination efficiency in the direct bandgap material of CdS and CdSe should be much higher than that of Si, which has an indirect bandgap.4. n-CdS NR/p-Si, n-CdSe NR/p-Si heterojunction PV devices and CdS NR/Au, CdSe NR/Au Schottky PV devices based on individual NRs were fabricated. Studing on PV devices based on individual1D nanostructures ont only provide a good platform for exploring the applications of nanomaterials in new energy convertion, but also supply energy for nano-optoelectronic integrated circuit. All these devices show excellent rectification characteristic in the dark and photovoltaic characteristics under light illumination. The conversion efficiency of n-CdS NR/p-Si, n-CdSe NR/p-Si heterojunction PV devices were1.24%and2.7%, respectively, under AM1.5G illumination. And these values for CdS NR/Au and CdSe NR/Au Schottky PV devices were3.8%and4.1%, respectively.5. CdS, CdSe, ZnTe and ZnSe1D nanostructures for nano-photodetection were studied. Three types PDs including photoconductor, heterojunction and Schottky junction, were constructed. The device structure-dependent performances were studied.(ⅰ) The responsivity, photoconductivity gain and response speed of CdS NR based photoconductor, heterojunction and Schottky junction were1.2×104A/W,100A/W,8A/W;3×104,260,20;>1/1s,300/740μs, 95/290μs, respectively,(ⅱ) The responsivity, photoconductivity gain and response speed of CdSe NR photoconductor, CdSe/ZnTe heteroj unction and CdSe/Au Schottky junction were2.1×104A/W,8.5A/W,1.2×103A/W;5.5×104,22,3×103;>1/1s,37/118μs,110/250μs, respectively,(ⅲ) The responsivity, photoconductivity gain and response speed of ZnTe NR photoconductor and ZnTe/Si heterojunction were4.8×104A/W,1.8×103A/W;1.2×105,4.2x103;5/12ms,790/960μs, respectively,(ⅳ) The responsivity, photoconductivity gain and response speed of ZnSe NR photoconductor were2.39×105A/W,6.44×105and0.5s, respectively. It’s found that the photoconductor PD has advantage of responsivity and photoconductivity gain; heterojunction and Schottky junction PDs have advantage of response speed.6. Nonvolatile memory were fabricated by constructing CdSe NW/Au Schottky junctions, and multibit nonvolatile memory based on single CdSe NW and memory devices based on flexible and transparent substrate were also fabricated. These memory devices show high performance of their storage characteristics such as their high-resistance on/off ratio (>104), long retention time (>104s), low operating voltage (2V) and superior stability (>8months). The resistive switching of CdSe NW/Au Schottky devices is understood by electron trapping and detrapping in the interfacial oxide layer. These results confirm that the CdSe:Ga NW/Au Schottky memory devices exhibit excellent mechanical flexibility as well as good memory properties, revealing their suitability for flexible transparent electronic device applications.