Stimuli-responsive and self-healing supramolecular Zn(II)-guanosine metal-organic gel for Schottky barrier diode application

Spontaneous formation of a supramolecular metal-organic hydrogel using unsubstituted guanosine as a ligand and Zn2+ ions is reported. Guanosine, in the presence of NaOH, self-assembled into a stable G-quadruplex structure, which underwent crosslinking through Zn2+ ions to afford a stable hydrogel. The gel has been characterized using several spectroscopic as well as microscopic studies. The hydrogel demonstrated excellent stimuli responsiveness towards various chemicals and pH. Furthermore, the gel exhibited intrinsic thixotropic behavior and showed self-healing and injectable properties. The optical properties of the Zn-guanosine metallo-hydrogel suggested a semiconducting nature of the gel, which has been exploited for fabricating a thin film device based on a Schottky diode interface between metal and a semiconductor. The fabricated device shows excellent charge transport characteristics and linear rectifying behavior. The findings are likely to pave the way for newer research in the area of soft electronic devices fabricated using materials synthesized by employing simple biomolecules.

High performance photodetector based on CdS/CdS0.42Se0.58nanobelts heterojunction

The ternary alloy CdSxSe1-xcombines the physical properties of CdS and CdSe, and its band gap can be adjusted by changing the element composition. The alloy has charming photoelectric properties as well as potential application value in photoelectric devices. In this work, the CdS/CdS0.42Se0.58nanobelt (NB) heterojunction device was prepared by chemical vapor deposition combined with a typical dry transfer technique. The heterojunction photodetector shows high light switching ratio of 6.79 × 104, large spectral responsivity of 1260 A W-1, high external quantum efficiency of 2.66 × 105% and large detectivity of 7.19 × 1015cm Hz1/2W-1under 590 nm illumination and 3 V bias. Its rise and decay time is about 45/90μs. The performance of the heterojunction photodetector was comparable or even better than that of other CdS(Se) based photodetector device. The results indicate that the CdS/CdS0.42Se0.58NB heterojunction possesses a promising potential application in high performance photodetectors.

Review on Quasi One-Dimensional CdSe Nanomaterials: Synthesis and Application in Photodetectors

During the past 15 years, quasi one-dimensional (1D) Cadmium Selenide (CdSe) nanomaterials have been widely investigated for high-performance electronic and optoelectronic devices, due to the unique geometrical and physical properties. In this review, recent advancements on diverse synthesis methods of 1D CdSe nanomaterials and the application in photodetectors have been illustrated in detail. First, several bottom-up synthesis methods of 1D CdSe nanomaterials have been introduced, including the vapor-liquid-solid method, the solution-liquid-solid method, and electrochemical deposition, etc. Second, the discussion on photodetectors based on 1D CdSe nanomaterials has been divided into three parts, including photodiodes, photoconductors, and phototransistors. Besides, some new mechanisms (such as enhancement effect of localized surface plasmon, optical quenching effect of photoconductivity, and piezo-phototronic effect), which can be utilized to enhance the performance of photodetectors, have also been elaborated. Finally, some major challenges and opportunities towards the practical integration and application of 1D CdSe nanomaterials in photodetectors have been discussed, which need to be further investigated in the future.

Influence of interface inhomogeneity on the electrical transport mechanism of CdSe nanowire/Au Schottky junctions

Schottky junctions based on one-dimensional semiconductor nanomaterials, such as nanowires (NWs) and nanobelts (NBs), have been widely used in building high-performance nano-electric and nano-optoelectric devices during the past 15 years. Meanwhile, with considerable development in diverse application fields, more and more interests are turning to the investigation of the fundamental physics inside the junctions. The inhomogeneity of the interface between semiconductor NWs/NBs and metal electrodes has significant influence on the electrical transport mechanism of Schottky junctions. However, few researchers are involved in such studies and the physical mechanism here is far from fully understood. In this work, we fabricated Schottky junctions based on single CdSe NWs, in which Au was used as a Schottky contact with CdSe NW. The temperature dependence of the electrical transport characteristics of typical CdSe NW/Au Schottky junctions were characterized. The ideality factor was found to decrease and the zero-bias Schottky barrier height (SBH) increased monotonously as the temperature was increased from 140 to 320 K, and this relationship was ascribed to SBH inhomogeneity. The electrical transport mechanism was analyzed quantitatively with a spatial potential fluctuation model, in which SBHs obey the Gaussian distribution. The standard deviation of the SBH distribution was determined to be as high as 13.54% and 13.94% of the zero-bias mean SBH in the temperature ranges 140-200 K and 200-320 K, respectively. Our work revealed the barrier inhomogeneity at CdSe NW/Au interfaces and its influence on the electrical transport mechanism of NW-based Schottky junctions.

Guided CdSe Nanowires Parallelly Integrated into Fast Visible-Range Photodetectors

One-dimensional semiconductor nanostructures, such as nanowires (NWs), have attracted tremendous attention due to their unique properties and potential applications in nanoelectronics, nano-optoelectronics, and sensors. One of the challenges toward their integration into practical devices is their large-scale controlled assembly. Here, we report the guided growth of horizontal CdSe nanowires on five different planes of sapphire. The growth direction and crystallographic orientation are controlled by the epitaxial relationship with the substrate as well as by a graphoepitaxial effect of surface nanosteps and grooves. CdSe is a promising direct-bandgap II-VI semiconductor active in the visible range, with potential applications in optoelectronics. The guided CdSe nanowires were found to have a wurtzite single-crystal structure. Field-effect transistors and photodetectors were fabricated to examine the nanowire electronic and optoelectronic properties, respectively. The latter exhibited the fastest rise and fall times ever reported for CdSe nanostructures as well as a relatively high gain, both features being essential for optoelectronic applications.

Present perspectives of broadband photodetectors based on nanobelts, nanoribbons, nanosheets and the emerging 2D materials

Recent research on photodetectors has been mainly focused on nanostructured materials that form the building blocks of device fabrication. The selection of a suitable material with well-defined properties forms the key issue for the fabrication of photodetectors that cover different ranges of the electromagnetic spectrum. In this review, the latest progress in light detection using nanobelts, nanoribbons, nanosheets and the emerging two-dimensional (2D) materials is reviewed. Particular emphasis is placed on the detection of light by the hybrid structures of the mentioned nanostructured materials in order to enhance the efficiency of the light-matter interaction. The booming research area of black phosphorus based photo-detection is also reviewed. This review provides an overview of basic concepts and new directions towards photodetectors, and highlights potential for the future development of high performance broadband photodetectors.

Nanostructured Photodetectors: From Ultraviolet to Terahertz

Inspired by nanoscience and nanoengineering, numerous nanostructured materials developed by multidisciplinary approaches exhibit excellent photoelectronic properties ranging from ultraviolet to terahertz frequencies. As a new class of building block, nanoscale elements in terms of quantum dots, nanowires, and nanolayers can be used for fabricating photodetectors with high performance. Moreover, in conjunction with traditional photodetectors, they exhibit appealing performance for practical applications including high density of integration, high sensitivity, fast response, and multifunction. Therefore, with the perspective of photodetectors constructed by diverse low-dimensional nanostructured materials, recent advances in nanoscale photodetectors are discussed here; meanwhile, challenges and promising future directions in this research field are proposed.

CdSe Nanowire-Based Flexible Devices: Schottky Diodes, Metal-Semiconductor Field-Effect Transistors, and Inverters

Novel CdSe nanowire (NW)-based flexible devices, including Schottky diodes, metal-semiconductor field-effect transistors (MESFETs), and inverters, have been fabricated and investigated. The turn-on voltage of a typical Schottky diode is about 0.7 V, and the rectification ratio is larger than 1 × 10(7). The threshold voltage, on/off current ratio, subthreshold swing, and peak transconductance of a typical MESFET are about -0.3 V, 4 × 10(5), 78 mV/dec, and 2.7 μS, respectively. The inverter, constructed with two MESFETs, exhibits clear inverting behavior with the gain to be about 28, 34, and 38, at the supply voltages (V(DD)) of 3, 5, and 7 V, respectively. The inverter also shows good dynamic behavior. The rising and falling times of the output signals are about 0.18 and 0.09 ms, respectively, under 1000 Hz square wave signals input. The performances of the flexible devices are stable and reliable under different bending conditions. Our work demonstrates these flexible NW-based Schottky diodes, MESFETs, and inverters are promising candidate components for future portable transparent nanoelectronic devices.

Surface plasmon propelled high-performance CdSe nanoribbons photodetector

In this work, we present a plasmonic photodetector (PPD) with high sensitivity to red light illumination. The ultrasensitive PPD was composed of high-crystalline CdSe nanoribbons (NRs) decorated with plasmonic hollow gold nanoparticles (HGNs) on the surface, which were capable of coupling the incident light due to localized surface plasmon resonance (LSPR). Device analysis reveals that after modification of HGNs, both responsivity and detectivity were considerably improved. Further device performance analysis and theoretical simulation based on finite element method (FEM) find that the optimized performance is due to HGNs induced localized field enhancement and direct electron transfer.

Fast and low-temperature synthesis of one-dimensional (1D) single-crystalline SbSI microrod for high performance photodetector

A new rapid and low temperature hydrothermal process has been developed for the synthesis of one-dimensional single-crystalline SbSI microrods with high quality and high photodetecting performance.

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

p-type ZnTe:Ga nanowires with a tunable electrical conductivity can be used to fabricate a high-performance semiconductor/graphene Schottky diode photodetector.

Gap states assisted MoO3 nanobelt photodetector with wide spectrum response

Molybdenum oxides have been widely investigated for their broad applications ranging from electronics to energy storage. Photodetectors based on molybdenum trioxide (MoO3), however, were seldom reported owing to their low conductivity and weak photoresponse. Herein we report a photodetector based on single MoO3 nanobelt with wide visible spectrum response by introducing substantial gap states via H2 annealing. The pristine MoO3 nanobelt possessed low electrical conductance and no photoresponse for nearly all visible lights. The H2 annealing can significantly improve the conductance of MoO3 nanobelt, and result in a good photodetector with wide visible spectrum response. Under illumination of 680 nm light, the photodetector exhibited high responsivity of ~56 A/W and external quantum efficiency of ~10200%. As corroborated by in situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy investigations, such strong wide spectrum photoresponse arises from the largely enriched gap states in the MoO3 nanobelt after H2 annealing.