Efficient Semiconductor Research Articles

Comprehensive Evaluation for Protective Coatings: Optical, Electrical, Photoelectrochemical, and Spectroscopic Characterizations

Numerous efficient semiconductors suffer from instability in aqueous electrolytes. Strategies utilizing protective coatings have thus been developed to protect these photoabsorbers against corrosion while synergistically improving charge separation and reaction kinetics. Recently, various photoelectrochemical (PEC) protective coatings have been reported with suitable electronic properties to ensure low charge transport loss and reveal the fundamental photoabsorber efficiency. However, protocols for studying the critical figures of merit for protective coatings have yet to be established. For this reason, we propose four criteria for evaluating the performance of a protective coating for PEC water-splitting: stability, conductivity, optical transparency, and energetic matching. We then propose a flow chart that summarizes the recommended testing protocols for quantifying these four performance metrics. In particular, we lay out the stepwise testing protocols to evaluate the energetics matching at a semiconductor/coating/(catalyst)/liquid interface. Finally, we provide an outlook for the future benchmarking needs for coatings.

Toward More Efficient Organic Semiconductors: The Relationship between Morphology, Charge Transport, and Photophysical Properties

In recent years, materials science has been facing an electronics revolution due to the fast progress in the development of organic semiconductors. In this context, the current study attempts to tune the photophysical properties of polycyclic aromatic hydrocarbons (PAHs) by engineering their morphology and size. Four families of PAHs─oligoacenes, circulenes, triangulenes, and sunflowers─are considered to investigate the evolution of their optoelectronic properties with size and morphology. Based on the calculated properties, several quantitative structure–property relationships have been established for the prediction of reorganization energy. It is found that morphologies like circulene and triangulene that are less aromatic and have smaller energy gaps achieve smaller reorganization energy and thus are better candidates for charge transport materials. For all considered PAHs, the excitation energies of the strongest low-lying electronic transition (β peak) span in the visible region and demonstrate the size tunability. The β peak of some oligoacene and triangulene families exhibits plasmonic behavior that is important for the fabrication of lighter optical devices compared with metallic systems. We have also explored the effect of sulfur heteroatoms on the structural, electronic, and optical properties of circulene and sunflower morphologies.

Beam Parameter Product Optimization for High Power SWIR Laser Diode Stack Fiber Coupling

An optimized setup for fiber optic injection of a kilowatt peak power laser diode stack emitting in the SWIR spectral range is proposed. Starting from a fast axis collimated (FAC) and slow axis collimated (SAC) 15 bars, 19 emitters off the shelf laser diode stack, the beam is transformed using spatial beam combining and polarization coupling. Both techniques integrated in a compact design enable to couple the kilowatt level beam into a standard 600 μm core, 0.22 numerical aperture (NA) multimode optical fiber. An application in the field of long range SWIR laser illuminator for gated viewing is presented. A comparison between two illuminators is realized both based on the same laser diode stack but one using beam parameter product (BPP) reduction and one without. It could be demonstrated that BPP reduction is the best way for efficient, narrow divergence and compact semi-conductor based laser illuminators design and realization. The global laser illuminator efficiency could be improved by 75% for the narrowest divergences thanks to this approach.

Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review

In the last decades photocatalysis has become one of the most employed technologies for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are transition metal oxides, in which the band structure allows charge carrier separation upon solar irradiation. The photoinduced charge carrier can thus cause oxidative and reductive redox reactions at the surface, inducing the formation of the radical species able to initiate the AOPs. Despite the great advantages of this process (non-toxic, cheap and environmentally clean), the main drawback lies in the fact that the most efficient semiconductors are only able to absorb UV irradiation, which accounts for only 5% of the total solar irradiation at the Earth’s surface and not enough to generate the required amount of electron-hole pairs. On the other hand, many efforts have been devoted to the sensitization of wide band gap transition metal oxides to visible light, which represents a higher percentage (almost 45%) in the solar electromagnetic spectrum. Among all the strategies to sensitize transition metal oxides to visible irradiation, doping with lanthanides has been less explored. In this regard, lanthanides offer a unique electronic configuration, consisting in 4f orbitals shielded by a 5s5p external shell. This occurrence, coupled with the different occupation of the localized 4f orbitals would provide an astounding opportunity to tune these materials’ properties. In this review we will focus in depth on the modification of two promising photocatalytic transition metal oxides, namely ZnO and ZrO2, with cerium, europium and erbium atoms. The aim of the work is to provide a comprehensive overview of the influence of lanthanides on the structural, optical and electronic properties of the modified materials, emphasizing the effect of the different 4f orbital occupation in the three considered doping atoms. Moreover, a large portion of the discussion will be devoted to the structural-properties relationships evidencing the improved light absorption working mechanism of each system and the resulting enhanced photocatalytic performance in the abatement of contaminants in aqueous environments.

Tuning Polymer Semiconductor Morphology through Additive Engineering for a Stable Phototransistor

The application of PTB7-Th polymer as an efficient semiconductor material in a phototransistor (PT) has been demonstrated, with a strategy to improve the hole transport and enhance the device stability under dark as well as illumination conditions. The results have been established using two solvent additives, namely 1,8-diiodooctane (DIO) and 1,8-dibromooctane (DBrO) which have the ability to modulate the polymer morphology. These additives also improve the charge transport properties and help in achieving higher mobility in organic field effect transistors (OFETs). The DIO and DBrO-modified devices show an increase in mobility (0.09 and 0.22 cm2/V-s, respectively) with respect to the control device (without any additive). Further, the device stability in the dark as well as under illumination improves drastically for the DBrO-modified device, whereas photodegradation of the DIO-modified device is observed. The photophysical studies, AFM, FESEM, XRD, and electrical investigations were carried out to understand the effect of the solvent additive in lowering the contact resistance, suppressing traps, and improving the morphology. With the optimized concentration of DBrO as the solvent additive, a PTB7-Th based PT is implemented and a responsivity of 688 A/W is obtained.

Interface Chelation Induced by Pyridine‐Based Polymer for Efficient and Durable Air‐Processed Perovskite Solar Cells

AbstractPolymer doping is a significant approach to precisely control nucleation and crystal growth of perovskites and enhance electronic quality in perovskite solar cells (PSC) prepared in air. Here, a brand‐new self‐healing polysiloxane (SHP) with dynamic 2,6‐pyridinedicarboxamide (PDCA) coordination units and plenty of hydrogen bonds was designed and incorporated into perovskite films. PDCA units, showing strong intermolecular Pb2+‐Namido, I−‐Npyridyl, and Pb2+‐Oamidocoordination interactions, were expected to enhance crystallinity and passivate the grain boundary. In addition, abundant hydrogen bonds in SHP afforded the self‐healing of cracks at grain boundaries for fatigue PSCs. Significantly, the doped device demonstrated a champion efficiency of 19.50 % with inconspicuous hysteresis, almost rivaling those achieved in control atmosphere. This strategy of heterocyclic‐based macromolecular doping in PSCs will pave a way for realizing efficient and durable crystalline semiconductors.

Interface Chelation Induced by Pyridine-Based Polymer for Efficient and Durable Air-Processed Perovskite Solar Cells.

Polymer doping is a significant approach to precisely control nucleation and crystal growth of perovskites and enhance electronic quality in perovskite solar cells (PSC) prepared in air. Here, a brand-new self-healing polysiloxane (SHP) with dynamic 2,6-pyridinedicarboxamide (PDCA) coordination units and plenty of hydrogen bonds was designed and incorporated into perovskite films. PDCA units, showing strong intermolecular Pb2+ -Namido , I- -Npyridyl , and Pb2+ -Oamido coordination interactions, were expected to enhance crystallinity and passivate the grain boundary. In addition, abundant hydrogen bonds in SHP afforded the self-healing of cracks at grain boundaries for fatigue PSCs. Significantly, the doped device demonstrated a champion efficiency of 19.50 % with inconspicuous hysteresis, almost rivaling those achieved in control atmosphere. This strategy of heterocyclic-based macromolecular doping in PSCs will pave a way for realizing efficient and durable crystalline semiconductors.

Strategic fabrication of efficient photo-responsive semiconductor electronic diode-devices by Bovine Serum Albumin protein-based Cu(II)-metallohydrogel scaffolds

Bovine Serum Albumin protein-based two fascinating functional self-healing Cu(II) metallohydrogel scaffolds (MD1 and MD2) have been studied for the development of metal-semiconductor junction based Schottky diode device. Multiple metal-semiconductor (MS) junction devices, offering the sandwich-like configuration of Indium tin oxide (ITO)/ metallogel/Aluminium (Al), have been made-up to investigate the electrical properties of the synthesized metallohydrogel materials. Optical characterizations including optical band gap measurement have been carried out using Tauc's equation for both the metallohydrogels. The current-voltage (I-V) characteristics of just made-up devices are studied under irradiation and non- irradiation conditions to explore the electrical features through investigating the charge transport phenomenon. The electrical conductivity gets estimated as 3.13 × 10−5 S.m−1 and 2.69 × 10−5 S.m−1 for MD1 and MD2 under dark condition, and 11.06 × 10−5 S.m−1 and 5.99 × 10−5 S.m−1 for MD1 and MD2, respectively, in photo-irradiation. The measured optical and electrical properties of MD1 and MD2 metallohydrogels are thoroughly investigated and the data indicates that MD1 and MD2 metallohyrogels are semiconducting in nature with excellent photo-responsive behaviour. Moreover, the representative I − V characteristic of the MD1 and MD2 metallohydrogels at both irradiation and non-irradiation conditions represents the nonlinear rectifying behaviour, a typical signature for Schottky diode (SD).

Morphology controlling strategy of ZnS/CeO2 catalysts to enhance the photocatalytic performance for hydrogen production

Semiconductor photocatalysts have been utilized to convert solar energy into hydrogen. However, CeO 2 has been rarely reported as a photocatalyst for hydrogen production on account of the rapid photoelectron-hole pair recombination and limited visible light adsorption capacity. In this work, we present the morphology controlling strategy on the purpose of preparing efficient composite semiconductor photocatalysts of CeO 2 with regular shape and reliable performance. The synthesized photocatalysts ZnS/CeO 2 with completely different morphologies structure (ZnS/CeO 2 solid spheres and ZnS/CeO 2 hollow dodecahedra) were obtained by a similar method. The results show that with the expansion of the visible light absorption range and the increase of nano pore porosity, the two photocatalysts ZnS/CeO 2 can afford more active sites and promote the transfer of photogenerated electrons-holes, thus effectively improving the hydrogen production efficiency. Besides, both of the photocatalysts ZnS/CeO 2 exhibit the long term (25 ​h) stability that also indicates a great potential in the photocatalytic water splitting for hydrogen evolution. This work provides a new idea and research method for further research on hydrogen production from photolysis of water.

Efficient Optically-Pumped Semiconductor Optical Amplifier in a Coupled-Waveguide Configuration: A Novel Proposal

We propose an efficient scheme of optical pumping and a compact design of an optically-pumped semiconductor optical amplifier (OP-SOA), with gain characteristics which are qualitatively similar to that of conventional (electrically-pumped) SOA. The optical pump is coupled into the ‘active waveguide’ from an adjacent channel waveguide, called ‘pump waveguide’; by suitably tailoring the coupling between the two waveguides, selective transfer of pump power all along the active waveguide can be achieved. We show that optical pumping through the coupled-waveguide configuration is efficient over the existing schemes of optical pumping in semiconductors. The optical pump can be coupled into the pump waveguide through a separate fiber-pigtail, just as the signal is coupled to the active waveguide in commercially available SOA. Thus, the OP-SOA would be a stand-alone 3-port integrated optical device, without any electrical connections. The proposed scheme enables optical-to-optical gain control, in place of the current-controlled gain in conventional SOA. Performance characteristics of the OP-SOA are simulated for an InGaAsP/InP heterostructure device using a well-established model. It is found that for an input optical pump power of 25 dBm at the wavelength of 1310 nm, a small signal gain >30 dB is achieved at the wavelength of 1550 nm.

Optical heating of doped semiconductor nanocylinders supporting quasi-BIC modes

In the recent years, semiconductor and dielectric nanophotonic structures attracted a lot of attention for their resonant optical properties finding applications in thermal tuning and optical heating. Exciting high quality optical modes of both electric and magnetic nature in nanoresonators of high-index materials, one can effectively enhance optical absorption in such structures. Another big advantage of semiconductor materials is the ability to finely control the level of optical losses in visible and near infrared (near-IR) range through varying the doping level. In this work, we show theoretically that by moderate carrier doping of silicon via donors from group V materials one can achieve effective heating of nanoresonators. We show that by tuning the doping level of crystalline silicon supporting high quality non-radiative modes based on quasi bound states in the continuum one can achieve strong heating in near-IR under continuous wave regime illumination. We believe that our finding will pave the way for an efficient semiconductor near-IR all-optical sensors and nanoheaters.

Hurdles and recent developments for CdS and chalcogenide‐based electrode in “Solar electro catalytic” hydrogen generation: A review

AbstractThere are tremendous efforts to realize the idea of employing photoelectrochemical (PEC) technology for generating chemical energy from solar energy. The most important feature of this technology is to coordinate the energetics of an electrochemical reaction with the solar spectrum. So, the photoelectrochemistry of a semiconducting material plays a vital role in this arena. Exploring an efficient and stable semiconductor material for such purpose is an essential prospect. There are several sulfide selenide‐based semiconductors viz. II‐VI (Zn/Cd = S/Se) semiconductors those exhibit high potential in PEC application. Nonetheless, they suffer by certain corrosion issues, which are important to be reviewed and are discussed here. This review highlights the significant role of cadmium chalcogenides among various materials explored in this technology. CdS is the most studied system among all those with perfect band gap and band‐edge position exhibiting material, desired for photoanode in PEC cell. Next, recent progresses achieving enhancement in the performance of CdS photoanodes by doping, modifying the surface, morphology reconstruction, and engraving heterostructure is discussed in detail. The role of the nanostructured techniques, improved photo electrochemistry with redox couples, and advanced interfacial and band gap engineering is explored to overcome the lack of chemical stability of CdS. The review concludes with the bright scope of CdS as an efficient PEC material in the form of combined semiconductor systems with an optimum band gap, bandedge, and their complimentary properties rather than a single component material.

Optimizing the Electronic Structure of ZnS via Cobalt Surface Doping for Promoted Photocatalytic Hydrogen Production.

Developing highly efficient semiconductor photocatalysts for H2 evolution is intriguing, but their efficiency is subjected to the following three critical issues: limited light absorption, low carrier separation efficiency, and sluggish H2 evolution kinetics. Element surface doping is a feasible strategy to synchronously break through the above limitations. In this study, we prepared a series of Co-surface-doped ZnS photocatalysts to systematically investigate the effects of Co surface doping on photocatalytic activity and electronic structure. The implantation of Co results in the emergence of the impurity level above the valence band (VB) and the upshifted conduction band (CB) and enhances its visible light absorption. Co gradient doping inhibits the combination and facilitates the migration of carriers. S atoms are proven to be reactive active sites for photocatalytic H2 evolution over both ZnS and Co-doped ZnS. Co doping alters the surface electronic structure and decreases the absolute value for the hydrogen binding free energy (ΔGH) of the adsorbed hydrogen atom on the catalyst. As a consequence, Co-surface-doped ZnS shows boosted photocatalytic H2 evolution activity relative to the undoped material. This work provides insights into the mechanistic understanding of the surface element doping modification strategy to developing efficient photocatalysts.

Spectroscopic Assessment of Charge‐Carrier Mobility in Crystalline Organic Semiconductors

AbstractFurther progress in organic electronics demands new highly efficient organic semiconductor (OS) materials. So far, however, band‐like charge transport with high mobilities has been reliably demonstrated only in a few OSs, and development of efficient methods for search of high‐mobility materials among a plethora of OSs remains extremely important. In the present work, a spectroscopic method is presented for screening of crystalline OSs with efficient charge transport, to be used prior to time‐consuming device measurements. Specifically, the work focuses on a physical rationale and an experimental benchmark of a correlation between the intensities of the low‐frequency Raman spectrum and the strength of dynamic disorder limiting the charge‐carrier mobility in a material. As a result, two physics‐inspired spectroscopic descriptors for charge‐carrier mobility estimation are suggested, both of which clearly correlate with device mobilities reported for various crystalline OSs. It is anticipated that the spectroscopic method based on these descriptors can serve as a powerful search tool for revealing new high‐mobility OS materials.

Photonic crystal lasers: from photonic crystal surface emitting lasers (PCSELs) to hybrid external cavity lasers (HECLs) and topological PhC lasers [Invited

Photonic crystals (PhC) represent an important class of silicon photonics components employed as wavelength selective resonators to act as narrow-band mirrors in integrated lasers due to their small footprint, high surface area, and Q-factor/volume ratio that enables efficient confinement of light, required for improved performances of the laser. These properties of PhCs are key for the potential deployment of PhC based high power, energy efficient and versatile semiconductor lasers for telecom, datacom, optical sensing and biomedical applications. In this paper, we report the main advances on PhC based lasers from photonic crystal surface-emitting lasers (PCSELs) to the new hybrid external cavity laser (HECLs) configurations.

Steady-state and transient Raman gain coefficients of weakly-polar magnetoactive doped semiconductors

Assuming that the origin of stimulated Raman scattering (SRS) lies in third-order effective (Raman) susceptibility arising due to nonlinear induced polarization, we obtained expressions for steady-state and transient Raman gain coefficients of weakly-polar magnetoactive doped semiconductors under various geometrical configurations. The threshold pump intensity and optimum pulse duration for the onset of transient SRS are estimated. The dependence of Raman gain coefficients on doping concentration, external magnetostatic field, magnetostatic field inclination, scattering angle and pump pulse duration are explored in detail with aim to determine suitable values of these controllable parameters to enhance Raman gain coefficients at lower threshold intensities, and to search the feasibility of efficient semiconductor nonlinear devices based on Raman nonlinearities. Most expectedly, the technological potentiality of weakly-polar magnetoactive doped semiconductors as hosts for compression of scattered pulses and fabrication of efficient nonlinear devices such as frequency converters, Raman amplifiers and oscillators etc. based on Raman nonlinearities are established.

The role of synthesis method in hydrogen evolution activity of Ce doped ZnO/CNTs photocatalysts: A comparative study

Cerium doped zinc oxide/carbon nanotubes (Ce doped ZnO/CNTs) composites are synthesized using sol-gel, hydrothermal deposition and one-pot hydrothermal methods. These composites are tested for photocatalytic hydrogen evolution from water-methanol mixture to check the effect of synthesis method on photocatalytic activity of these composites. Each synthesis method induces unique physiochemical properties in composite and hydrogen evolution rates. The composite prepared by one-pot hydrothermal method shows highest hydrogen evolution of 759 μmolh−1g−1 under sunlight. This hydrogen evolution rate is significantly higher than the sol-gel synthesized photocatalyst (579 μmolh−1g−1) and hydrothermal deposition method (621 μmolh−1g−1). The high hydrogen evolution activity of the prepared composites can be attributed to small crystallite size, low recombination of charge carriers, large active surface area, short diffusion pathway for photoinduced electrons and high oxidation potential of photogenerated holes. Focused on different methods, this study provides a pathway for production of efficient semiconductor photocatalysts for environmental applications.

Modulation strategies in titania photocatalyst for energy recovery and environmental remediation

Among the various renewable sources of energy, solar energy is the most abundant and cleanest which can fulfill all our future energy demand. However, the stochastic nature of solar radiation hinders the continual utilization of that abundant energy. The strategic and effective usages of semiconductor-based photocatalysis can efficiently use this energy in different forms. Researchers have put great interest toward designing and constructing a highly efficient semiconductor photocatalyst to promote its real-life application potential to capture and utilize solar energy. It is very crucial to summarize the basics and advanced strategies to design and construct a semiconductor-based photocatalyst system. Herein, we have reviewed and summarized the state-of-the-art strategies and their basics to improve the photocatalytic activity of TiO2 in two aspects: (i) environmental remediation, and (ii) energy conversion. This review article focuses and answer three major queries of the reader i.e. (i) how to enhance and broaden the solar-light absorption range, (ii) how to design more surface-active sites, and (iii) how to slow down or inhibit the recombination of photogenerated charge carriers to promote the photocatalytic efficiency. Hence, this review article will give comprehensive knowledge of the design and construction of the TiO2 based photocatalyst and boost its efficiency towards energy recovery (CO2 conversion, N2 fixation, and H2 evolution), and environmental remediation (pollutant degradation, NOx conversion, and bacterial disinfection).

Microwave-assisted synthesis of ZnAl-LDH/g-C3N4 composite for degradation of antibiotic ciprofloxacin under visible-light illumination

Ciprofloxacin (CIP) is a fluoroquinolone family antibiotic pollutant. CIP existence in water environment has been rising very fast in day-to-day life and subsequently, it gives enormous health issues for humans because of its potent biological activity. To encounter this, current researchers are focusing on the development of highly efficient visible light semiconductor nanocomposites with potential photocatalytic activity. In the present work, we have successfully synthesized highly efficient zinc-aluminum layered double hydroxides with graphitic carbon nitride (ZALDH/CN) composites via a simple microwave irradiation method first time for the degradation of CIP under visible light. The fabricated materials are subsequently characterized by various spectroscopic techniques. UV–Vis DRS, TRFL, XRD, FT-IR, BET, FE-SEM, TEM, and XPS for optical, crystal structure, morphological, and elemental analysis. The main reactive intermediates which are formed during the photocatalytic degradation process were analyzed by LC-MS analysis. It is worth to note that, the optimized ZALDH/CN-10 composite showed the highest photo-degradation rate constant of 1.22 × 10−2 min−1 with 84.10% degradation is higher than bare CN and ZALDH photocatalysts. Based on the electron-hole pair trapping experiment results, possible CIP photo-degradation mechanism was also explained in the present study. With all results, this work demonstrates the ZALDH/CN composite materials showed a high synergistic effect with more specific surface area. Highest specific surface area leads to enhanced visible light adsorption capacity. Subsequently improved number of catalytically active sites. Furthermore, as compared with pure materials, composites of ZALDH/CN are having low electron-hole pair recombination. Consequently, the composites ZALDH/CN showed superior photocatalytic activity for antibiotic pollutant CIP degradation under visible-light illumination.

Distinguishing persistent effects in an undoped GaAs/AlGaAs quantum well by top-gate-dependent illumination

Persistent photoconductivity of GaAs/AlGaAs heterostructures has hampered the measurement of charge- and spin-related quantum effects in gate-defined quantum devices and integrated charge sensors due to Si-dopant-related deep donor levels (DX centers). In this study, this effect is overcome by using an undoped GaAs/AlGaAs heterostructure for photonic purposes. We also measure the electron transport before and after LED illumination at low temperatures. In addition to a regular rapid saturation showing the increased carrier density, a slow accumulation of illumination effects appeared when different top-gate voltages were applied during illumination, which indicated the redistribution of charge at the oxide–GaAs interface. This study provides interesting insights into the development of optically stable devices for efficient semiconductor quantum interfaces.