Di Wu

Device structure-dependent field-effect and photoresponse performances of p-type ZnTe:Sb nanoribbons

Sb-doped ZnTe nanoribbons (NRs) with enhanced p-type conductivity were successfully synthesized by a simple thermal co-evaporation method. Nanodevices, including nano-field-effect transistors (FETs) and nano-photodetectors (nanoPDs), were constructed based on the ZnTe:Sb NRs and their structure dependent device performances were systemically investigated. It is found that the transport properties of the ZnTe nanostructures as well as the device structures play a critical role in determining the device performances. In contrast to the nano-metal-oxide-semiconductor FETs (nanoMOSFETs) with back-gate structure, the top-gate nano-metal-insulator-semiconductor FETs (nanoMISFETs) show much enhanced performances in all aspects. On the other hand, owing to the appropriate p-type doping, nano-photodetectors (nanoPDs) based on the ZnTe:Sb NRs exhibit excellent device performances, such as high responsivity and photoconductive gain, fast response speed, large detectivity and so on. Moreover, the response time could be effectively shortened by using nano-heterojunction photodetectors (nanoHPDs). It is expected that knowledge gained from this work could be readily extended to nanodevices based on other nanostructures.

Self-powered and fast-speed photodetectors based on CdS:Ga nanoribbon/Au Schottky diodes

Self-powered photodetectors based on CdS:Ga nanoribbons (NR)/Au Schottky barrier diodes (SBDs) were fabricated. The as-fabricated SBDs exhibit an excellent rectification characteristic with a rectification ratio up to 106 within ±1 V in the dark and a distinctive photovoltaic (PV) behavior under light illumination. Photoconductive analysis reveals that the SBDs were highly sensitive to light illumination with very good stability, reproducibility and fast response speeds at zero bias voltage. The corresponding rise/fall times of 95/290 μs represent the best values obtained for CdS based nano-photodetectors. It is expected that such self-powered high performance SBD photodetectors will have great potential applications in optoelectronic devices in the future.

Chlorine-doped n-type CdS nanowires with enhanced photoconductivity

Cl-doped n-type CdS NWs with single-crystal wurtzite structure and [Formula: see text] growth direction were synthesized by using CdCl(2) as the dopant via a thermal co-evaporation method. By controlling the Cl vapor pressure during the growth, the conductivity of the CdS:Cl NWs can be tuned in a wide range of five orders of magnitude. A nano-photodetector based on the CdS:Cl NWs shows high sensitivity to visible light with excellent stability and reproducibility. Significantly, the photoconductivity of the CdS NWs is greatly enhanced by Cl doping and the responsivity and photoconductive gain of the CdS:Cl NWs have substantially increased compared with the undoped CdS NWs. Further study also demonstrates the polarization-dependent photoconductivity of the CdS:Cl NWs. It is expected that the CdS:Cl NWs with tunable optoelectronic properties will have important applications in high-performance nano-optoelectronic devices.

Tuning the electrical transport properties of n-type CdS nanowiresvia Ga doping and their nano-optoelectronic applications

Gallium-doped n-type CdS nanowires (NWs) were successfully synthesized via a thermal evaporation method. The conductivities of the CdS NWs were dramatically improved by nearly nine orders of magnitude after Ga doping, and could be further tuned over a wide range by adjusting the doping level. High-performance metal-insulator-semiconductor field-effect transistors (MISFETs) were constructed based on the single CdS : Ga NW with high-κ Si(3)N(4) dielectrics and top-gate geometries. In contrast to back-gate FETs, the MISFETs revealed a substantial improvement in device performance. Nano-light emitting diodes (nanoLEDs) were fabricated from the CdS : Ga NWs by using a n-NW/p(+)-Si substrate hybrid device structure. The nanoLEDs showed a bright yellow emission at a low forward bias. It is expected that the Ga-doped CdS NWs with controlled electrical transport properties will have important applications in nano-optoelectronic devices.

High-performance CdS:P nanoribbon field-effect transistors constructed with high-κ dielectric and top-gate geometry

High-performance field-effect transistors (FETs) based on single phosphorus-doped n-type CdS nanoribbon with high-κ HfO2 dielectric and top-gate geometry were constructed. In contrast to the nano-FETs that were fabricated on SiO2/Si substrate with back-gate device configuration, the top-gate FETs exhibit a substantial improvement in performances, i.e., work voltage was reduced to a small value of within ±5 V, the subthreshold swing was reduced to 200 mV/dec and the Ion/Ioff ratio was increased by about six orders of magnitude. The top-gate CdS:P nano-FET shows high sensitivity upon light irradiation, revealing that the top-gate FETs are promising candidates for nanoelectronic and optoelectronic applications.

Construction of high-quality CdS:Ga nanoribbon/silicon heterojunctions and their nano-optoelectronic applications

Silicon based optoelectronic integration is restricted by its poor optoelectronic properties arising from the indirect band structure. Here, by combining silicon with another promising optoelectronic material, the CdS nanoribbon (NR), devices with heterojunction structure were constructed. The CdS NRs were also doped with gallium to improve their n-type conductivity. A host of nano-optoelectronic devices, including light emitting diodes, photovoltaic devices, and photodetectors, were successfully constructed on the basis of the CdS:Ga NR/Si heterojunctions. They all exhibited excellent device performances as regards high stability, high efficiency, and fast response speed. It is expected that the CdS NR/Si heterojunctions will have great potential for future applications of Si based optoelectronic integration.

Synthesis of high quality and stability CdS quantum dots with overlapped nucleation-growth process in large scale

A low-cost, green, and reproducibly non-injection one-pot synthesis of high-quality CdS quantum dots (QDs) is reported. The synthesis was performed in the open air by mixing precursors cadmium stearate and S powder into a new solvent N-oleoylmorpholine. An overlapped nucleation-growth stage followed by a dominated growth stage was observed. The resulting QDs exhibited well-resolved absorption fine substructure and a dominant band-edge emission with a narrow size distribution (the full width at half maximum (fwhm) was only 22-24nm). The maximum photoluminescence (PL) quantum yield (QY) was as high as 46.5%. Highly monodispersed CdS QDs with tunable sizes and similar PL fwhm and QYs could also be obtained from the CdS QDs in a large-scale synthesis. The high-resolution transmission electron microscopy (HRTEM) images and powder X-ray diffraction (XRD) pattern suggested that the as-prepared QDs with high crystallinity had a cubic structure. A significant PL improvement and a continuous QY increase for the CdS QDs were observed during a long storage time in air and in a glovebox under room temperature. A slow surface reconstruction was proposed to be the cause for the PL enhancement of CdS QDs.

Nano-Schottky barrier diodes based on Sb-doped ZnS nanoribbons with controlled p-type conductivity

ZnS nanoribbons (NRs) with controlled p-type doping were synthesized by using Sb as dopant. The p-type conductivity of the ZnS:Sb NRs could be tuned in a wide range of seven orders of magnitude by adjusting the Sb doping level. Nano-Schottky barrier diodes based on Al/p-ZnS NRs junctions exhibited excellent device performances with a high rectification ratio >107 and a small ideality factor of ∼1.22. The diodes also showed the potential as high-sensitive UV detectors. The p-ZnS NRs are expected to act as key building blocks in nano-optoelectronics.

Magnificent CdS three-dimensional nanostructure arrays: the synthesis of a novel nanostructure family for nanotechnology

Magnificent CdS three-dimensional nanostructure arrays, composed of caky plating made up of Cd micro-platelet arrays which are surrounded by an outer layer of well-aligned CdS nanowire/pillar arrays, were successfully prepared through a combination of electroplating and subsequent solvothermal reaction on Cd-coated copper substrates. The nucleation and growth behavior of CdS nanowire/pillars were qualitatively analyzed in terms of kinetics. The results demonstrated that the microstructure of the products shows great dependence on the synthetic conditions, including reactant concentration, growth temperature and time, and the morphological characteristics of the substrate. The coalescence growth of adjacent CdS nanowire/pillars during the growth stage was firstly demonstrated. In addition, the formation mechanism of caky Cd plating was well discussed and also a hydrogen bubbles-assisted growth mechanism based on electrochemistry was proposed to explain the unique plating. The relationship between the microstructure of the products and the synthetic conditions is beneficial for modifying the shape of CdS nanostructures. The as-prepared CdS three-dimensional nanostructure arrays are advantageous for their large surface area, highly ordered structure and conductive growth substrates, and thus may have great potential in many advanced material areas, especially in the field of solar cells.

Construction of crossed heterojunctions from p-ZnTe and n-CdSe nanoribbons and their photoresponse properties

Sb-doped p-type ZnTe nanoribbons (NRs) and Ga-doped n-type CdSe NRs were synthesized via a co-thermal evaporation method in a horizontal tube furnace, respectively. Crossbar heterojunction diode (HD) devices were constructed from p-ZnTe:Sb NRs and n-CdSe NRs by a convenient route. The p-ZnTe/n-CdSe NR HD device exhibits a significant rectification characteristic with a rectification ratio up to 103 within ±5 V and a low turn-on voltage of 2.6 V. Photoresponse analysis reveals that such HD devices were highly sensitive to light illumination with excellent stability, reproducibility and fast response speeds of 37/118 μs at reverse bias voltage. It is expected that such HD devices will have great potential applications in electronic and optoelectronic devices in the future.