Active Semiconductor Material Research Articles

Heterogeneously integrated light emitting diodes and photodetectors in the metal-insulator-metal waveguide platform

Abstract We demonstrate heterogeneous integration of active semiconductor materials into the conventional passive metal-insulator-metal (MIM) waveguides to provide compact on-chip light generation and detection capabilities for chip-scale active nanophotonic platforms. Depending on its bias conditions, a metal-semiconductor-metal section can function as either a light emitting diode or a photodetector directly connected to the MIM waveguides. We experimentally verify the independent and combined operations of electrically-driven on-chip light sources and photodetectors.

Deepening Insights into Near‐Infrared Excited‐State Intramolecular Proton Transfer Lasing: The Charm of Resonance‐Assisted Hydrogen Bonds

AbstractExcited‐state intramolecular proton transfer (ESIPT)‐active organic semiconductor materials, characterized by a or several resonance‐assisted hydrogen bonds (RAHBs), are supposed to be ideal candidates for achieving high‐performance near‐infrared (NIR) lasers. However, according to the energy gap law, the development of ESIPT‐active gain materials is still limited by the serious nonradiative decays. Herein, it is demonstrated that RAHBs can activate ESIPT lasing by inhibiting nonradiative decays. A new ESIPT‐active material 1,5‐dihydroxy‐2,6‐diphenylanthraquinone (DP‐DHAQ) containing two centrosymmetric RAHBs is developed, which exhibits a ≈100‐fold higher radiative decay rate (kr = 1.1 × 1010 s–1) in doped polystyrene (PS) film than that of 1‐hydroxy‐5‐methoxy‐2,6‐diphenylanthraquinone (DP‐HMAQ) and 1,5‐dimethoxy‐2,6‐diphenylanthraquinone (DP‐DMAQ), in which one and two RAHBs are broken, respectively, by introducing methyl groups. Both DP‐DHAQ and DP‐HMAQ can form four‐level systems based on the ESIPT processes, but only DP‐DHAQ doped PS microspheres exhibit laser emission at 710 nm under the test conditions. It is worth mentioning that single‐crystal microplates of DP‐DHAQ can realize NIR laser emission at 725 nm. The results suggest that RAHBs can effectively activate the gain property of ESIPT‐active materials, which deepens insights into NIR ESIPT lasing and provides a new proposal for the design of organic laser‐active molecules.

Core-Shell Engineered WO3 Architectures: Recent Advances from Design to Applications.

Ongoing efforts to design novel materials with efficient structure-property-performance relations prove challenging. Core-shell structures have emerged as novel materials with controlled production routes and highly tailorable properties that offer extensive advantages in advanced oxidation processing, particularly in photocatalysis and photoelectrochemical applications. WO3 , which is an optoelectronically active semiconductor material, is a popular material in current studies in the field of photo(electro)catalysis. Considerable progress has been made using core-shell WO3 architectures, which warrants an evaluation in terms of processing and preparedness for their use in versatile catalytic and energy storage applications. This paper presents an in-depth assessment of core-shell WO3 architectures by highlighting the design challenges and protocols in powder and thin-film chemical processing. The development of specific core-shell designs for use in targeted applications, such as H2 production, CO2 reduction, wastewater treatment, batteries, supercapacitors, and sensing, is analyzed. The fundamental role of WO3 in core-shell structures to enhance efficiency is also discussed, along with the limitations and improvement strategies. Further, the prospects of core-shell WO3 architectures in energy conversion and environmental applications are suggested.

Parity-time symmetry in monolithically integrated graphene-assisted microresonators.

Recently, optical systems with parity-time (PT) symmetry have attracted considerable attention due to its remarkable properties and promising applications. However, these systems usually require separate photonic devices or active semiconductor materials. Here, we investigate PT symmetry and exceptional points (EPs) in monolithically integrated graphene-assisted coupled microresonators. Raman effect and graphene cladding are utilized to introduce the balanced gain and loss. We show that PT-symmetry breaking and EPs can be achieved by changing the pump power and the chemical potential. In addition, the intracavity field intensities experience suppression and revival as the graphene-induced loss increases. Due to the unique distribution of optical field, tunable nonreciprocal light transmission is theoretically demonstrated when introducing the gain saturation nonlinearity. The maximum isolation ratio can reach 26 dB through optimizing the relevant parameters. Our proposed scheme is monolithically integrated, CMOS compatible, and exhibits remarkable properties for microscale light field manipulation. These superior features make our scheme has promising applications in optical communication, computing and sensing.

Computational analysis of novel high performance optically controlled RF switches for reconfigurable millimeterwave-to-THz circuits

Optically controlled RF switches with a novel non-contact device architecture that achieves high performance in the millimeterwave-to-terahertz (mmW-THz) region are proposed and investigated through simulation. The significant change in conductivity in semiconductors caused by photogenerated carriers is used to develop RF switches having very high performance. By including a thin layer of insulator between the active semiconductor material and the metal contacts, the carrier concentration can be enhanced over that of conventional devices. For a prototype demonstration, G-band coplanar waveguide-based optical switches (using Si and Ge as active materials) with different contact geometries have been modeled and simulated. The proposed switches outperform both conventional solid-state switches and phase-change material-based switches in the switch figure-of-merit, and are promising for developing a novel class of tunable and reconfigurable mmW-THz circuits for advanced sensing, imaging, and communication.

Advances in upconversion enhanced solar cell performance

Photovoltaics (PV) is the leading renewable energy harvesting technology. Thus, there is a remarkable strive to enhance the light harvesting capability of the state-of-the-art solar cells. The major issue common to all solar cell types is that they utilize only a limited portion of the solar spectrum, mostly in the visible range, as the active semiconductor materials suffer from intrinsic light absorption thresholds. As a result, photons below and above these threshold values do not contribute to the electricity generation. A plausible solution to enhance the performance is to integrate the PV cell with an upconverting (UC) component capable of harvesting lower energy photons in the infrared (IR) range and emitting visible light. The concept was first introduced in 1990s, but major progress in the field has been made in particular in the recent few years. In this overview our intention is to provide the readers with a comprehensive account of the progress in the research on the UC-enhanced solar cells. Lanthanide ions embedded in different host lattices constitute the most important UC material family relevant to the PV technology; we first summarize the design principles and fabrication routes of these materials. Then discussed are the different approaches taken to integrate the UC layers in actual PV device configurations. Finally, we will highlight the most prominent results obtained, give some future perspectives and outline the remaining challenges in this scientifically intriguing and application-wise important field.

Aluminum-doped zinc oxide–coated 3D spacer fabrics with electroless plated copper contacts for textile thermoelectric generators

The technology of electroless metal plating was investigated for coating of three-dimensional spacer fabrics with copper (Cu) serving as contact layers. A subsequent etching process allowed the structuring of the spacer fabrics and thus the exposure of the spacer threads, which were coated with the thermoelectrically active semiconductor material aluminum-doped zinc oxide (Al:ZnO or AZO). For this, the atomic layer deposition was used. The material combination AZO/Cu used for a single thermoelectric-active element with a size of 30 × 30 mm2 worked as a small thermoelectric generator and showed a maximum output power of 0.16 μW at a temperature difference of 62 K. AZO as an alternative non-toxic thermoelectric material exhibited a temperature-dependent Seebeck coefficient (e.g. 55 μV/K for ΔT = 50 K).

Temperature‐Gradient‐Controlled Method Enabling Shape Control of 2D Perovskite Single Crystals for Photodetection

2D hybrid organic–inorganic lead halide perovskites have been reported as promising photodetection active semiconductor materials due to their excellent photoelectric properties and stability. However, the solution growth of 2D crystal materials is affected adversely by narrow process windows, low process reproducibility, and small crystal sizes. Herein, a temperature‐gradient‐controlled method to grow high‐quality 2D perovskite crystals on the order of centimeters is developed. Using this new method, BA2PbI4 and mixed‐cation BA2FAxMA1−xPb2I7 crystals are produced with shape control and improved quality at the bottom of the precursor solution. Subsequently, their photoelectric responses are investigated comprehensively. Photodetectors based on these single crystals exhibit outstanding performances, affording 10−11 A dark current, > 103 on–off ratio, ≈10 mA W−1 responsivity, excellent stability, and linear photoresponse. Moreover, the annealing of crystals effectively reduces the dark current of the detectors. The mixed‐cation BA2FA0.4MA0.6Pb2I7 crystal demonstrates improved photoelectric response and a significant change in morphology.

Surface Roughness Effects of Pd‐loaded Magnetic Microspheres on Reduction Kinetics of Nitroaromatics

Metal nanoparticles decoration on magnetically active semiconductor materials is a common strategy to improve the colloidal stability, catalyst harvesting, and reuse. In this study, a surfactant‐free solvothermal method followed by a heat treatment to prepare highly surface roughened α‐Fe2O3 (Hematite)/Pd microspheres (MSPs) is reported. Amine‐functionalized silicate sol‐gel matrix is used as a stabilizing agent for the solvothermal synthesis of Prussian blue (PB) MSPs using HCl at 80 °C for 20 h. It is observed that modulating HCl concentration in a medium led to a high degree of improvement in surface roughness. Employing heat treatment at 350 °C for 6 h, PB MSPs are transformed into α‐Fe2O3, Hematite phase. Fabricated Hematite/Pd MSPs have shown high catalytic reduction activity over p‐nitrophenol. Reduction kinetics of nitroaromatics is monitored using UV‐vis absorption spectroscopy and product formation is confirmed by 1H and 13C NMR analyses.

Bottom gate ZnO-TiO2 thin film transistor fabrication using a Rf-sputtering technique on Si and glass substrates

ZnO thin films were fabricated by an RF-sputtering deposition technique on Si and Glass substrate and then was used as the active semiconductor material in thin-film transistors (TFTs). The TFTs were fabricated in a bottom gate with top contact electrode structure with high-k TiO2 as the gate insulator and Au used for the source and drain electrodes but Al for the gate electrode. TFTs were annealed at 500 °C for 1 h using sputtering inside the substrate heating facility. The TFT with a W/L (4/1) channel ratio found high field-effect mobility of is 5.19 cm 2 /Vs and drain current on–off ratio at 10 7 with a low threshold voltage.

Morphological exploration of chemical vapor–deposited P-doped ZnO nanorods for efficient photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is beneficial and has received attractive attention due to a greater potential to generate hydrogen and oxygen from water by using plentiful solar light to solve the problem of energy crisis. Various active semiconductor materials are used in PEC water splitting applications. Nevertheless, in past decades, most of the researchers suggested that titanium oxide (TiO2) is the best photoanode for this type of applications. Now, Zinc oxide (ZnO) is considered a perfect substitution to TiO2 due to its comparable energy band structure and superior photogenerated electron transfer rate. In this study, bare and phosphorous-doped ZnO nanorods were successfully developed on fluorine-doped tin oxide-coated glass (FTO) substrate by chemical vapor deposition. X-ray diffraction (XRD) pattern authenticated hexagonal structure formation with strong diffraction peak of (101), which showed that ZnO nanorods were perfectly developed along c axis. The optical and morphological properties were analyzed by UV–Vis and scanning electron microscopy images. The energy-dispersive X-ray spectra demonstrated that doping agent phosphorous was present in ZnO nanorods. The PEC properties of the developed ZnO nanorods were further investigated and obtained results suggested that a small amount of phosphorous-doped ZnO nanorods enhances their PEC performance.

Structural and optical properties of (Zn,Mn)O thin films prepared by atomic layer deposition

This paper investigates manganese-doped zinc oxide (ZnMnO) thin films grown using the atomic layer deposition (ALD) technique. ZnO and MnO layers were deposited alternatively using diethyl zinc and manganese (III) acetylacetonate (Mn(acac)3) as metallic precursors. A suppressed growth rate for both materials was observed during the growth of ZnMnO samples, which is due to reduced adsorption of the precursor molecules on the surface of the sample. Structural characterization of the ZnMnO films shows a weak polycrystalline structure for the as-deposited thin films. On the other hand, thermally annealed samples demonstrated a textured polycrystalline structure with a distinct (002) orientation. A red shift in the near band edge absorption was observed by increasing the Mn:Zn ratio. The results of this work demonstrate the potential in ALD growth of high-quality wide bandgap ZnMnO thin films that can be used as an active semiconductor material in memory and logic devices.

Comparative analysis between numerical simulation of PPV/PCBM and InGaN based solar cells

Solar cells are promising renewable and without carbon electric energy asset to address the non-renewable energy source and fissile fuel shortage. Indium Gallium Nitride (InGaN thin films are now a day’s attracting researchers because of its possible use as an active semiconductor material and its immense application potential in short wavelength optoelectronic solar cells. InGaN also exhibits attractive photovoltaic (optical and electrical) properties. In this paper we had a Comparative Analysis between Numerical simulation of organic and inorganic solar cell. We have chosen Indium Gallium Nitride (InGaN) and PPV/PCBM-based solar cells. In our work we are going to find out optimization points for both of the solar cells. The characteristics of PV figures of merits of PPV solar cells simulated with the composition of polymer [6.6]-phenyl C61 butyric acid methyl ester (PCBM) to demonstrate maximum efficiency. Comparative analysis of both organic and inorganic solar cells demonstrates their pros and cons as organic solar cells are coming with good economy but low efficiency. If we are looking towards Inorganic solar cells they are having good efficiency but economically Costlier.

Surfactant-assisted hydrothermally synthesized novel TiO2/SnS@Pd nano-composite: structural, morphological and photocatalytic activity

To meet the increasing demand of energy and to conquer the waste water problems, fabrication of visibly active semiconductor materials is demand of the present world. In this paper, we have synthesized the surfactant-assisted novel TiO2/SnS@Pd by adopting the energy-efficient hydrothermal approach and the photocatalytic activity of the synthesized composites were tested by taking the Rhodamine B (RhB) as the model pollutant. The structural, optical, morphological and compositional properties were elaborated using the various characterization techniques. X-ray photoelectron spectroscopy and high-resolution transmission electron microscope were used to find out the formation of ternary composites. The formation of heterojunction and red shift in the absorption of the ternary composite were the rationale behind the highest photocatalytic activity of sample containing the 4% SnS and 2% Pd for the removal of RhB. The complete removal of pollutant was achieved only in 30 min using the ternary composite. It was also found that the binary samples exhibited the maximum removal of dye in the basic medium while the ternary composite exhibited the maximum removal of dye in neutral medium because of leaching of Pd in alkaline medium. The role of active species towards the degradation of dye was also studied. The synthesized materials are highly beneficial for the fabrication or development of cost-effective device for the waste water treatment.

Visible-Light Photocatalytic H2Production Activity of β-Ni(OH)2-Modified CdS Mesoporous Nanoheterojunction Networks

Photocatalytic water splitting for hydrogen production is an emerging and promising strategy for converting solar energy into chemical fuels. To that end, the development of robust and highly active semiconductor materials is of eminent importance in this field. Here, we demonstrate high-surface-area mesoporous networks comprising interconnected β-Ni(OH)2 modified CdS nanocrystals (NCs) as highly active and stable photocatalysts for hydrogen generation. Compared to single-component CdS assemblies, Ni-modified materials present a strong enhancement of photocatalytic performance for hydrogen evolution under visible light irradiation (λ ≥ 420 nm). By controlling the formation of β-Ni(OH)2 species, the mesoporous β-Ni(OH)2/CdS heterojunction networks at a 10 wt % Ni content reached an outstanding photocatalytic H2-evolution rate of 1.4 mmol h–1 at 20 °C (or ∼35 mmol g–1 h–1 mass activity), associated with an apparent quantum yield (QY) of 72% at 420 nm in a 5 M NaOH aqueous solution containing 10% v/v ethanol...

Photoelectrochemical Properties of N-Doped Graphene/Hematite Composites

Photocatalytic and photoelectrochemical (PEC) water splitting are gaining huge interests for its ability to convert solar energy directly into fuel (hydrogen) in a simple, cost-effective and cleaner manner. However, lack of more active, stable and robust semiconductor materials for water oxidation with good light absorption and low charge recombination rate hampers this technology from large-scale application. Hematite (α- Fe2O3) is one of the favorable materials for PEC water oxidation as it possesses a suitable band gap of about 2.0 eV, moderate stability in a broad pH range, absorbs more than 40% of incident solar spectrum, and is less-toxic and less expensive. However, it suffers from poor electronic conductivity, low absorption coefficient, short hole diffusion length (< 10 nm), and high electron-hole recombination rate, which results in a relatively low solar-to-chemical energy efficiency which limits its practical applications.[1 ] At the other end, graphene commands special interest in PEC applications as it is a zero-band-gap material with outstanding electronic conductivity of 106 Scm-1 and optoelectronic properties (98% transmittance).[2 ]In addition, graphene with its exceptional charge carrier mobility can be used as mediators for electron transport thus resulting in better carrier separation[3 ]. In this work, we discuss the development and PEC properties of graphene and nitrogen-doped graphene-based photo anode with non-toxic, low-cost hematite for enhanced water oxidation capability and increased life time. Graphene is used as the conductive layer here to promote charge collection and transport by accepting photogenerated electrons from the semiconductor oxide. Substituting nitrogen on to graphene is found to be particularly interesting as it results in dramatically altered graphene band structure. To prepare graphene, an electrochemical exfoliation route is carried out in a two electrodes system. Graphite flake and Pt rod is used as working and counter electrode respectively. Na2SO4 aqueous solution or (NH4)2SO4 /ammonia solution is used in the exfoliation in order to obtain graphene or N-doped graphene. A constant voltage of +10 V (vs. Ag/AgCl) was applied on the system to initiate the exfoliation. To understand the effect of synthesis route on the PEC properties, α- Fe2O3 is synthesized by three different routes such as flame spray pyrolysis (FSP), e-beam evaporation and hydrothermal method. The physical properties of graphene, N-doped graphene and α- Fe2O3 are characterised by XPS, XRD, SEM and TEM. Photo anodes are fabricated in two steps: i) a conductive layer is formed by coating graphene/N-doped graphene layers on quartz substrates and ii) a photocatalyst layer is sprayed coated or grown over this conductive layer depending on the synthesis method. The effect of synthesis route on the PEC properties of photo anodes such as I-V characteristics and impedance spectroscopy under dark and 1-sun illumination determined using a 3-electrode cell with Pt-foil as counter electrode and Ag/AgCl as reference electrode in 1 M NaOH is discussed. References Kevin Sivula, Florian Le Formal, and Michael Gratzel, Solar Water Splitting: Progress Using Hematite (α- Fe2O3) Photoelectrodes, ChemSusChem 2011, 4, 432Guancai Xie , Kai Zhang , Beidou Guo , Qian Liu , Liang Fang , and Jian Ru Gong , Graphene-Based Materials for Hydrogen Generation from Light-Driven Water Splitting, Adv. Mater. 2013, 25, 3820Zhang, Lili, Hongrui Hu, Mingzai Wu, Xinxin Yu, Zhaoqi Sun, Guang Li, Xiansong Liu, and Xiuwen Zheng, A novel bubbling-assisted exfoliating method preparation of magnetically separable γ- Fe2O3/graphene recyclable photocatalysts, Functional Materials Letters, 2014, 7, 1450056

Mind the mobilities

Organic Devices The operational speed of devices such as transistors depends on how fast charge carriers move through their active semiconductor material. In a Perspective, McCulloch et al. discuss how several recent claims of very high carrier mobilities in organic semiconductors overstate the values by at least an order of magnitude. These indirect measurements based on the transistor devices themselves can be flawed because the modeling of the current flow is inadequate. Science , this issue p. [1521][1] [1]: /lookup/doi/10.1126/science.aaf9062

CuWO4 Nanoflake Array-Based Single-Junction and Heterojunction Photoanodes for Photoelectrochemical Water Oxidation.

Over recent years, tremendous efforts have been invested in the search and development of active and durable semiconductor materials for photoelectrochemical (PEC) water splitting, particularly for photoanodes operating under a highly oxidizing environment. CuWO4 is an emerging candidate with suitable band gap and high chemical stability. Nevertheless, its overall solar-to-electricity remains low because of the inefficient charge separation process. In this work, we demonstrate that this problem can be partly alleviated through designing three-dimensional hierarchical nanostructures. CuWO4 nanoflake arrays on conducting glass are prepared from the chemical conversion of WO3 templates. Resulting electrode materials possess large surface areas, abundant porosity and small thickness. Under illumination, our CuWO4 nanoflake array photoanodes exhibit an anodic current density of ∼0.4 mA/cm(2) at the thermodynamic potential of water splitting in pH 9.5 potassium borate buffer--the largest value among all available CuWO4-based photoanodes. In addition, we demonstrate that their performance can be further boosted to >2 mA/cm(2) by coupling with a solution-cast BiVO4 film in a heterojunction configuration. Our study unveils the great potential of nanostructured CuWO4 as the photoanode material for PEC water oxidation.

Analytical study of pulsed laser irradiation on some materials used for photovoltaic cells on satellites

The present research concerns on the study of laser-powered solar panels used for space applications. A mathematical model representing the laser effects on semiconductors has been developed. The temperature behavior and heat flow on the surface and through a slab has been studied after exposed to nano-second pulsed laser. The model is applied on two different types of common active semiconductor materials that used for photovoltaic cells fabrication as silicon (Si), and gallium arsenide (GaAs). These materials are used for receivers’ manufacture for laser beamed power in space. Various values of time are estimated to clarify the heat flow through the material sample and generated under the effects of pulsed laser irradiation. These effects are theoretically studied in order to determine the performance limits of the solar cells when they are powered by laser radiation during the satellite eclipse. Moreover, the obtained results are carried out to optimize conversion efficiency of photovoltaic cells and may be helpful to give more explanation for layout of the light-electricity space systems.

Sensitivity of the threshold voltage of organic thin-film transistors to light and water

Analyses of extensive experiments with organic thin-film transistors (OTFTs) indicate that the threshold voltage VT of an OTFT has a temporal differential sensitivity. In particular, VT changes initially by changing the light illumination intensity or making/removing a contact of water with the organic semiconductor. Keeping the conditions stationary, then the initial shift of VT diminishes, since the time dependence of VT gradually recovers the OTFT to the state before applying the change in the environmental conditions. While still causing a differential and time-variant shift of VT, the deionized water does not have a dramatic impact on OTFTs that use the polymer DKPP-βT (diketopyrrolopyrrole β-unsubstituted quaterthiophene) as the active semiconductor material. Observations for the impact of water are made from experiments with an OTFT that has a microfluidic channel on the top the electrical channel, with the water in the microfluidic channel in direct contact with the electrical channel of the OTFT. This arrangement of electrical and microfluidic channels is a novel structure of the microfluidic OTFT, suitable for sensing applications of liquid analytes by means of organic electronics.