Longhui Zeng

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.

Core-shell heterojunction of silicon nanowire arrays and carbon quantum dots for photovoltaic devices and self-driven photodetectors.

Silicon nanostructure-based solar cells have lately intrigued intensive interest because of their promising potential in next-generation solar energy conversion devices. Herein, we report a silicon nanowire (SiNW) array/carbon quantum dot (CQD) core-shell heterojunction photovoltaic device by directly coating Ag-assisted chemical-etched SiNW arrays with CQDs. The heterojunction with a barrier height of 0.75 eV exhibited excellent rectifying behavior with a rectification ratio of 10(3) at ±0.8 V in the dark and power conversion efficiency (PCE) as high as 9.10% under AM 1.5G irradiation. It is believed that such a high PCE comes from the improved optical absorption as well as the optimized carrier transfer and collection capability. Furthermore, the heterojunction could function as a high-performance self-driven visible light photodetector operating in a wide switching wavelength with good stability, high sensitivity, and fast response speed. It is expected that the present SiNW array/CQD core-shell heterojunction device could find potential applications in future high-performance optoelectronic devices.

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.

High-responsivity UV-Vis Photodetector Based on Transferable WS2 Film Deposited by Magnetron Sputtering.

The two-dimensional layered semiconducting tungsten disulfide (WS2) film exhibits great promising prospects in the photoelectrical applications because of its unique photoelectrical conversion property. Herein, in this paper, we report the simple and scalable fabrication of homogeneous, large-size and transferable WS2 films with tens-of-nanometers thickness through magnetron sputtering and post annealing process. The produced WS2 films with low resistance (4.2u2009kΩ) are used to fabricate broadband sensitive photodetectors in the ultraviolet to visible region. The photodetectors exhibit excellent photoresponse properties, with a high responsivity of 53.3u2009A/W and a high detectivity of 1.22u2009×u20091011 Jones at 365u2009nm. The strategy reported paves new way towards the large scale growth of transferable high quality, uniform WS2 films for various important applications including high performance photodetectors, solar cell, photoelectrochemical cell and so on.

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.

Bilayer graphene based surface passivation enhanced nano structured self-powered near-infrared photodetector.

A simple methyl-terminated (-CH(3)) surface passivation approach has been employed to enhance the performance of the bilayer graphene/Si nanohole array (BLG/SiNH array) Schottky junction based self-powered near infrared photodetector (SPNIRPD). The as-fabricated SPNIRPD exhibits high sensitivity to light at near infrared region at zero bias voltage. The I(light)/I(dark) ratio measured is 1.43 × 10(7), which is more than an order of magnitude improvement compared with the sample without passivation (~6.4 × 10(5)). Its corresponding responsivity and detectivity are 0.328 AW(-1) and 6.03 × 10(13) cmHz(1/2)W(-1), respectively. The demonstrated results have confirmed the high-performance SPNIRPD compared with the photo-detectors of similar type and its great potential application in future optoelectronic devices.

High-speed ultraviolet-visible-near infrared photodiodes based on p-ZnS nanoribbon–n-silicon heterojunction

Ag-doped p-type ZnS nanoribbons (NRs) with a high hole concentration of 5.1 × 1018 cm−3 and high carrier mobility of 154.0 cm2 V−2 s−1 were synthesized by using silver sulfide (Ag2S) as the Ag source. Excellent ohmic contact to p-ZnS NR with specific contact resistivity as low as 5.6 × 10−7 Ω cm2 was achieved by using bilayer Cu (4 nm)–Au electrode, which according to the depth profiling X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) analysis can help to form a thin Cu2S interfacial layer between the electrode. Based on the high quality ZnS NRs and achievement on ohmic contact, p–n photodiodes have been constructed from the p-ZnS nanoribbon (NR)–n-Si heterojunction with a response speed as high as ∼48 μs (rise time). Furthermore, the device also exhibits stable optoelectrical properties with high sensitivity to UV-visible-NIR light and an enhancement of responsivities of 1.1 × 103 AW−1 for 254 nm under a reverse bias of 0.5 V. These generality of the above results shows that the p-ZnS NR–n-Si heterojunction will have potential applications in future high-performance photodetectors.

High-performance nonvolatile Al/AlO(x)/CdTe:Sb nanowire memory device.

Here we demonstrate a room temperature processed nonvolatile memory device based on an Al/AlO(x)/CdTe:Sb nanowire (NW) heterojunction. Electrical analysis shows an echelon hysteresis composed of a high-resistance state (HRS) and a low-resistance state (LRS), which can allow it to write and erase data from the device. The conductance ratio is as high as 10⁶, with a retention time of 3 × 10⁴ s. Moreover, the SET voltages ranged from +6 to +8 V, whilst the RESET voltage ∼0 V. In addition, flexible memory nano-devices on PET substrate with comparable switching performance at bending condition were fabricated. XPS analysis of the Al/AlO(x)/CdTe:Sb NW heterojunction after controlled Ar⁺ bombardment reveals that this memory behavior is associated with the presence of ultra-thin AlO(x) film. This Al/AlO(x)/CdTe:Sb NW heterojunction will open up opportunities for new memory devices with different configurations.

Surface charge transfer induced p-CdS nanoribbon/n-Si heterojunctions as fast-speed self-driven photodetectors

Heterojunctions composed of single p-type CdS nanoribbons (NRs) and n-type silicon (Si) were successfully fabricated. The p-type CdS NRs were realized through a facile surface charge transfer doping approach. A typical as-fabricated p–n heterojuction exhibits excellent rectifying behavior with a rectification ratio up to ∼2 × 103 within ±1.5 V, a low turn-on voltage of ∼0.5 V and a small ideality factor of 1.29. Furthermore, due to the strong photovoltaic effect, the heterojunction is found to be highly sensitive to visible light irradiation at zero bias voltage with a large Ilight/Idark ratio (2 × 103), fast response speed (tr = 26 μs and tf = 112 μs), good reproducibility and long-term stability. The present work suggests great potential of such a heterojunction for future high-speed photodetector applications, and more importantly, signifying the feasibility of applying the surface charge transfer doping technique for constructing novel nano-optoelectronic devices.