Ji-Gang Hu

Monolayer Graphene Film on ZnO Nanorod Array for High‐Performance Schottky Junction Ultraviolet Photodetectors

A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free-standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) film. The single-crystalline [0001]-oriented ZnONR array has a length of about 8-11 μm, and a diameter of 100∼600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I-V characteristics in the temperature range of 80-300 K, the barrier heights of the MLG film/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG film/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices.

Monolayer Graphene/Germanium Schottky Junction As High-Performance Self-Driven Infrared Light Photodetector

We report on the simple fabrication of monolayer graphene (MLG)/germanium (Ge) heterojunction for infrared (IR) light sensing. It is found that the as-fabricated Schottky junction detector exhibits obvious photovoltaic characteristics, and is sensitive to IR light with high Ilight/Idark ratio of 2 × 10(4) at zero bias voltage. The responsivity and detectivity are as high as 51.8 mA W(-1) and 1.38 × 10(10) cm Hz(1/2) W(-1), respectively. Further photoresponse study reveals that the photovoltaic IR detector displays excellent spectral selectivity with peak sensitivity at 1400 nm, and a fast light response speed of microsecond rise/fall time with good reproducibility and long-term stability. The generality of the above results suggests that the present MLG/Ge IR photodetector would have great potential for future optoelectronic device applications.

Light trapping and surface plasmon enhanced high-performance NIR photodetector

Heterojunctions near infrared (NIR) photodetectors have attracted increasing research interests for their wide-ranging applications in many areas such as military surveillance, target detection, and light vision. A high-performance NIR light photodetector was fabricated by coating the methyl-group terminated Si nanowire array with plasmonic gold nanoparticles (AuNPs) decorated graphene film. Theoretical simulation based on finite element method (FEM) reveals that the AuNPs@graphene/CH3-SiNWs array device is capable of trapping the incident NIR light into the SiNWs array through SPP excitation and coupling in the AuNPs decorated graphene layer. What is more, the coupling and trapping of freely propagating plane waves from free space into the nanostructures, and surface passivation contribute to the high on-off ratio as well.

Fabrication of p-type ZnSe:Sb nanowires for high-performance ultraviolet light photodetector application

p-type ZnSe nanowires (NWs) with tunable electrical conductivity were fabricated on a large scale by evaporating a mixed powder composed of ZnSe and Sb in different ratios. According to the structural characterization, the Sb-doped ZnSe NWs are of single crystalline form and grow along the [001] direction. The presence of Sb in the ZnSe NWs was confirmed by XPS spectra. Electrical measurement of a single ZnSe:Sb NW based back-gate metal-oxide field-effect-transistor reveals that all the doped NWs exhibit typical p-type conduction characteristics, and the conductivity can be tuned over eight orders of magnitude, from 6.36 × 10(-7) S cm(-1) for the undoped sample to ∼37.33 S cm(-1) for the heavily doped sample. A crossed p-n nano-heterojunction photodetector made from the as-doped nanostructures displays pronounced rectification behavior, with a rectification ratio as high as 10(3) at ±5 V. Remarkably, it exhibits high sensitivity to ultraviolet light illumination with good reproducibility and quick photoresponse. Finally, the work mechanism of such a p-n junction based photodetector was elucidated. The generality of the above result suggests that the as-doped p-type ZnSe NWs will find wide application in future optoelectronics devices.

The Effect of Plasmonic Nanoparticles on the Optoelectronic Characteristics of CdTe Nanowires

In this work, a simple strategy is proposed to improve the device performance of photodetector by modifying plasmonic nanoparticles onto the surface of semiconductors nanostructure. Both experimental analysis and theoretical simulation show that the plasmonic metal nanoparticles (AuNPs) exhibits obvious localized surface plasmon resonance (LSPR) which can trap incident light efficiently, leading to enhanced photocurrents and improved performance of photoelectronic devices. It is also observed that the AuNPs modified CdTeNW photodetector exhibit apparent sensitivity to 510 nm light, to which pure CdTeNWs is virtually blind. What is more, after AuNPs decoration, the response speed of the photodetector is increased substantially from 6.12 to 1.92 s. It is believed that this result will open up new doors for manipulating light and further improving the efficiency of semiconductor nanostructures based optoelectronic devices.

p-CdTe nanoribbon/n-silicon nanowires array heterojunctions: photovoltaic devices and zero-power photodetectors

Nano-heterojunction composed of single Sb-doped p-type CdTe nanoribbon (CdTeNR) and n-type silicon nanowires (SiNWs) array was successfully fabricated. The p–n heterojunction exhibited excellent rectifying behavior with a rectification ratio of 105 at ±2 V in the dark. Due to the matched band gap of CdTeNR with SiNWs, as well as the efficient light absorption of the SiNWs array, pronounced photovoltaic characteristics with energy conversion efficiency up to 2.1% under AM 1.5 G was achieved. Furthermore, the heterojunction device could serve as high-performance zero-power photodetector operated in the visible to near-infrared (NIR) range with good stability, high sensitivity, and fast response speed. It is expected that the p-CdTeNR/n-SiNWs array heterojunctions will find important applications in future nano-optoelectronic devices.

Flexible CuS nanotubes–ITO film Schottky junction solar cells with enhanced light harvesting by using an Ag mirror

Here we report the fabrication of a novel photovoltaic device based on CuS nanotubes (CuSNTs) and indium tin oxide (ITO) Schottky junctions. Large-quantity synthesis of CuSNTs was accomplished via a solution-based sacrificial template method under moderate conditions, while ITO Schottky contacts were fabricated via micro-fabrication and pulsed laser deposition (PLD). Upon light illumination, CuSNTs-ITO Schottky junctions exhibited pronounced photovoltaic behavior, giving rise to a power conversion efficiency of 1.17% on a conventional SiO(2)/Si substrate. Furthermore, by utilizing PET as the substrate, transparent and flexible CuSNTs-ITO solar cells were constructed and showed performance close to their device counterparts on a rigid substrate. Notably, it was found that the flexible devices were robust against tensile strain and could stand a bending angle up to ∼95°. To enhance the light absorption of the devices, an Ag mirror layer was deposited on the rear side of the PET substrate so as to allow multiple reflection and absorption of the incident light. As a result, the flexible devices showed a substantial performance improvement, yielding an efficiency of ∼2%. Our results demonstrate that low-cost and environmentally friendly CuSNTs-ITO solar cells are promising candidates for new-generation photovoltaic devices.

p-type ZnTe:Ga nanowires: controlled doping and optoelectronic device application

Although significant progress has been achieved in the synthesis and doping of ZnTe nanostructures, it remains a major challenge to rationally tune their transport properties for nanodevice applications. In this work, p-type ZnTe nanowires (NWs) with tunable conductivity were synthesized by employing Ga/Ga2O3 as a dopant via a simple thermal evaporation method. Electrical measurements of back-gate metal-oxide field-effect-transistors based on a single NW revealed that when the Ga content in the ZnTe NWs increases from 1.3 to 5.1 and 8.7%, the hole mobility and hole concentration will increase from 0.0069 to 0.33 to 0.46 cm2 V−1 s−1, respectively. It was also found that the photodetector composed of a ZnTe:Ga NW/graphene Schottky diode exhibited high sensitivity to visible light illumination with an on/off ratio as high as 102 at reverse bias, with good reproducibility. The responsivity and detectivity were estimated to be 4.17 × 103 A W−1 and 3.19 × 1013 cm Hz1/2 W−1, higher than other ZnTe nanostructure based photodetectors. It is expected that the ZnTe:Ga NWs with controlled p-type conductivity are promising building blocks for fabricating high performance nano-optoelectronic devices in the future.

High performance nonvolatile memory devices based on Cu2−xSe nanowires

We report on the rational synthesis of one-dimensional Cu 2−xSe nanowires (NWs) via a solution method. Electrical analysis of Cu 2−xSe NWs based memory device exhibits a stable and reproducible bipolar resistive switching behavior with a low set voltage (0.3–0.6 V), which can enable the device to write and erase data efficiently. Remarkably, the memory device has a record conductance switching ratio of 108, much higher than other devices ever reported. At last, a conducting filaments model is introduced to account for the resistive switching behavior. The totality of this study suggests that the Cu 2−xSe NWs are promising building blocks for fabricating high-performance and low-consumption nonvolatile memory devices.

Gallium doped n-type ZnxCd1-xS nanoribbons: Synthesis and photoconductivity properties

Gallium doped ZnxCd1-xS nanoribbons (NRs) with controlled composition were synthesized on Au-coated Si (100) substrates by a simple thermal co-evaporation method. The composition of ZnxCd1-xS:Ga NRs can be simply controlled by the distance of the substrates from the source powder. The grown NRs exhibit excellent crystallinity, with growth direction along [0002]. It is found that the gallium doping can remarkably enhance the conductivity of ZnxCd1-xS:Ga NRs, leading to obvious n-type conduction behavior. It is also observed that the ZnxCd1-xS:Ga NRs show sensitive photoresponse to visible light illumination with excellent stability and reproducibility. The generality of this study suggests the great potential of the ZnxCd1-xS:Ga NRs for future optoelectronics application.