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In this work comparative analysis of the effect of various active materials and use of photonic crystal in active layer of organic photodetector in the wavelength range between 400 nm and 700 nm is described. The active organic material used in the photodetector is PH3T: PCBM. The various materials used for the analysis of absorbance and transmittance between the active layer are nc_ZnO organic material and Al2O3, GaAs and silicon nitride (Si3N4) semiconductor materials. The maximum absorbance reported in this work are 80.0969%, 80.0451%, 75.4784%, 80.8878%, 76.8223% for without PC on nc_ZnO organic layer, with nc_ZnO PC on nc_ZnO layer, Al2O3, GaAs and silicon nitride (Si3N4) semiconductor materials with PC. The absorption is almost flat between 70% and 80% for without PC and for with PC having materials nc_ZnO, Al2O3 and GaAs between the wavelength range 450 nm to 630 nm. We have achieved an improvement in the absorption at wavelength ranging from 630 nm to 700 nm by using PC with nc_ZnO organic material.

Semiconductor Quantum Dots have unique properties, such as the quantum size effect that provide the breakthrough in optoelectronic devices. The small effective mass of electron and hole open-up an avenue of wide bandgap tunability in InAs Quantum Dots (QDs), making them an attractive material for solar cell application. Therein, 4x4 Luttinger Kohn Hamiltonian method is used to calculate the absorption co-efficient of epitaxially grown InAs QDs. Further, we studied the size-dependent absorption co-efficient and the barrier material model of InAs QDs capping with InP and GaAs. Our theoretical simulation predicts the efficiency of InAs/GaAs and InAs/InP system in the intrinsic layer of p-i-n structure solar cells.

The multilevel storage capability of nonvolatile resistive random access memory (ReRAM) is greatly desired to accomplish high functioning memory density. In this study, Ta2O5 thin film with different thicknesses (2, 4, and 6 nm) was exploited as an appropriate interfacial barrier layer for limiting the formation of the interfacial layer between the 10 nm thick sputtering deposited resistive switching (RS) layer and Ta ohmic electrode to improve the switching cycle endurance and uniformity. Results show that lower forming voltage, narrow distribution of SET-voltages, good dc switching cycles (103), high pulse endurance (106 cycles), long retention time (104 s at room temperature and 100°C), and reliable multilevel resistance states were obtained at an appropriate thickness of ∼2 nm Ta2O5 interfacial barrier layer instead of without Ta2O5 and with ∼4 nm, and ∼6 nm Ta2O5 barrier layer, ZrO2-based memristive devices. Besides, multilevel resistance states have been scientifically investigated via modulating the compliance current (CC) and RESET-stop voltages, which displays that all of the resistance states were distinct and stayed stable without any considerable deprivation over 104 s retention time and 104 pulse endurance cycles. The I-V characteristics of RESET-stop voltage (from −1.7 to −2.3 V) of HRS are found to be a good linear fit with the Schottky equation. It can be seen that Schottky barrier height rises by increasing the stop-voltage during RESET-operation, resulting in enhancing the data storage memory window (on/off ratio). Moreover, RESET-voltage and CC control of HRS and LRS revealed the physical origin of the RS mechanism, which entails the formation and rupture of conducting nanofilaments. It is thoroughly investigated that proper optimization of the barrier layer at the ohmic interface and the switching layer is essential in memristive devices. These results demonstrate that the ZrO2-based memristive device with an optimized ∼2 nm Ta2O5 barrier layer is a promising candidate for multilevel data storage memory applications.

International audience; Producing ultrathin light absorber layers is attractive towards the integration of lightweight planar components in electronic, photonic, and sensor devices. In this work, we report the experimental demonstration of a thin gold (Au) metallic metasurface with near-perfect visible absorption (~ 95 %). Au nanoresonators possessing heights from 5-15 nm with sub-50 nm diameters were engineered by block copolymer (BCP) templating. The Au nanoresonators were fabricated on an alumina (Al2O3) spacer layer and a reflecting Au mirror, in a film-coupled nanoparticle design. The BCP nanopatterning strategy to produce desired heights of Au nanoresonators was tailored to achieve nearperfect absorption at ≈ 600 nm. The experimental insight described in this work is a step forward towards realizing large area flat optics applications derived from subwavelengththin metasurfaces.

In the last few decades, smart windows made from VO2-based thermochromic films have attracted extensive attention, but their actual commercial applications are limited by low luminous transmittance (Tlum), low solar modulation ability (ΔTsol), high phase transition temperature (Tc), and poor durability. In this study, glass/HfO2/VO2/HfO2 tri-layer films were designed and deposited on glass substrates by pulse laser deposition. Crystal structures, surface morphology, surface roughness, electrical properties, and optical properties of as-prepared sandwich structure films were analyzed. Results showed that both HfO2 buffer layer and antireflection layer (ARL) were monoclinic phase and grew along the (020) and (−111) crystal planes, respectively. HfO2 buffer layer not only reduced Tc of VO2 film by about 20 °C, but also played an important role in regulating crystal quality and surface morphology of VO2 films. More importantly, by covering films with HfO2 ARL, Tlum and ΔTsol of VO2 film were greatly improved. In particular, when the thicknesses of HfO2 buffer layer and ARL were 80 nm and 120 nm, the obtained HfO2/VO2/HfO2 tri-layer film reached a balance between high Tlum (∼47.2%), high ΔTsol (∼9.1%) and low Tc (∼49.1 °C). In addition, after 216 h of boiling water treatment, Tlum and ΔTsol of HfO2/VO2/HfO2 film covered with 120 nm thick ARL still remained at 49.3% and 7.0%, showing excellent durability. This research provides a new strategy for designing VO2-based smart windows with high performance and good durability.

As a high-k material, hafnium oxide (HfO2) has been used in gate dielectrics for decades. Since the discovery of polar phase in Si-doped HfO2 films, chemical doping has been widely demonstrated as an effective approach to stabilize the ferroelectric phase in HfO2 based thin films. However, the extra capping layer deposition, post-growth annealing and wake-up effect are usually required to arouse the ferroelectricity in HfO2 based thin films, resulting in the increase of complexity for sample synthesis and the impediment of device application. In this study, the ferroelectricity is observed in non-capped dopant-free HfO2 thin films prepared by pulsed laser deposition (PLD) without post-growth annealing. By adjusting the deposited temperature, oxygen pressure and thickness, the maximum polarization up to 14.7 μC/cm2 was obtained in 7.4 nm-thick film. The fraction of orthorhombic phase, concentrations of defects and size effects are considered as possible mechanisms for the influences of ferroelectric properties. This study indicates that PLD is an effective technique to fabricate high-quality ferroelectric HfO2 thin films in the absence of chemical doping, capping layer deposition and post-growth annealing, which may boost the process of nonvolatile memory device application.

Antimony sulfide (Sb2S3) is an appealing semiconductor as light absorber for solar cells due to its high absorption coefficient, appropriate band gap (~1.7 eV) and abundance of constituent elements. However, power conversion efficiency (PCE) of Sb2S3-based solar cells still lags much behind the theoretically predicted due to the imperfect energy level alignment at the charge transporting layer/Sb2S3 interfaces and hence severe charge recombination. Herein, we insert a high-temperature sintered magnesium (Mg)-doped tin oxide (SnO2) layer between cadmium sulfide (CdS) and fluorine doped tin oxide to form a cascaded energy level alignment and thus mitigate interfacial charge recombination. Simultaneously, the inserted Mg-doped SnO2 buffer layer facilitates the growth of the neibouring CdS film with orientation followed by Sb2S3 film with larger grains and fewer pinholes. Consequently, the resultant Sb2S3 solar cells with Mg-doped SnO2 deliver a champion PCE of 6.31%, 22.8% higher than those without a buffer layer. Our work demonstrates that deliberate absorber growth as well as efficient hole blocking upon an appropriate buffer layer is viable in obtaining solution-processed Sb2S3 solar cells with high performance.

In the present era of data-driven architectures like 5G, Internet of things (IoT), Artificial Intelligence (AI), etc, the requirement of fast-switchable memory storage is more than ever. Oxide resistive switches are considered to be a primary choice in the non-volatile memory design. In this work, we have engineered the conventional metal-insulator-metal (MIM) structure of an oxide memristor (Ag/ZnO/ITO) by inducing an additional oxide layer La0.7Sr0.3MnO3 (LSMO) at the interface between the active layer (ZnO) and Ag electrode. The presence of LSMO acts as a reservoir for the oxygen vacancies, easing the conducting filament formation process in ZnO, thereby enabling drastic improvement of the switching performance and offering reliable endurance over multiple switching cycles. First-principles-based calculations suggested the role of Oxygen vacancies in controlling the electronic state of ZnO and formation of vacancies in the resistive switching process, which is in agreement with the experimental observation. The current results pave ways for improving the switching performance of resistive memory circuits through simple structural engineering incorporation, which lies at the heart of oxide electronics.

Metal oxide semiconductor (MOS) thin films are promising sensing layer for integration in gas sensor devices for detecting toxic and harmful molecules. Herein, tungsten oxide (WO3) thin films are deposited on interdigital electrodes by vacuum thermal evaporation to realize batch fabrication of high-performance gas sensors. Subsequent annealing at different temperatures allows for regulation of the concentration of oxygen vacancies in the WO3 films, which has been found to exert a great influence on the sensor properties. In addition, the surface structure of WO3 films is also highly dependent on the annealing temperature. Gas sensing investigations show that the WO3 sensor annealed at 500 °C possesses the best sensing properties for detecting triethylamine (TEA) including very high response, good selectivity, fast response, and low limit of detection (63 ppb). The excellent sensor performances are attributed to the enhanced adsorption of oxidative oxygen species due to the presence of abundant oxygen vacancies. The scalable fabrication of WO3 thin film gas sensors and the oxygen vacancy engineering strategy proposed herein may shed some light to developing high performance environmental sensors.

In this letter, a miniaturized-element dual-polarized frequency selective rasorber (FSR with independently regulated dual-transmission response has been presented. The proposed FSR is made of two cascaded layers separated by an air spacer, where the top lossy layer provides wideband absorption along with in-band transmission and the bottom lossless layer exhibits a dual bandpass filter. The novelty of the proposed design lies in the use of lumped capacitors in the top layer to realize the independently controlled highly selective transmission frequencies as well as attain a miniaturized unit cell topology (having dimensions of 0.08L 0.08L, L being the lowest operating frequency . In addition, convoluted slot geometries are patterned in the bottom layer to obtain the transmission bands appearing at the same frequencies as that of the top layer. The proposed structure has an operating range of 1.87 - 7.97 GHz, whereas two distinct transmission responses are located at 3.52 GHz and 5 GHz having insertion losses of 1.2 dB and 0.82 dB, respectively. Further, the geometry exhibits an angularly stable performance upto 45o for both TE and TM polarizations. A prototype of the proposed FSR was fabricated and measured to validate the simulated responses under normal incidence

Flexible and transparent conductive films are highly desirable in some optoelectronic devices, such as smart windows, touch panels, as well as displays and electromagnetic protection field. Silver nanowire (Ag NW) has been considered as the best material to replace indium tin oxide (ITO) to fabricate flexible transparent electromagnetic interference (EMI) shielding films due to its superior comprehensive performance. However, the common substrates supporting Ag NWs require surface modification to enhance the adhesion with Ag NWs. In this work, a flexible and transparent Ag NWs EMI shielding film with sandwich structure through a facile rod-coating method, wherein Ag NWs network were embedded between biodegradable gelatin-based substrate and cover layer. The interfacial adhesion between Ag NWs and gelatin-based layers was enhanced by hydrogen-bonding interaction and swelling effect without any pretreatment. The shielding effectiveness (SE) of the G/Ag NW/G (G represents gelatin-based layer) film reaches 37.74 dB at X band with an optical transmittance of 72.0 %. What’s more, the flexible gelatin-based layer and encapsulated structure endow the resultant G/Ag NW/G film integrating excellent mechanical properties, reliable durability, antioxidation, as well as anti-freezing performance. This work paves a new way for fabricating flexible transparent EMI shielding films.

This article presents an ultracompact bandpass filter (BPF) realized by slow wave substrate integrated groove gap waveguide (SW-SIGGW). The SW-SIGGW is composed of two layers of the dielectric substrate, in which periodic mushroom-type electromagnetic band-gap (EBG) unit cells are employed as packaging structures. The gap layer is realized by the upper substrate, and the via-patch mushrooms are designed on the lower substrate. Due to the slow wave structure in the form of periodical metallic via-holes designed on the lower substrate, the guided wavelength is reduced by about 52.8% compared with normal SIGGW. A dual-band resonator and a cascaded second-order BPF are designed based on SW-SIGGW. Compared with the conventional second-order SIGGW BPF, the proposed SW-SIGGW BPF achieves a 62.6% reduction in the area. By adopting vertical stacking technology, the area of the SW-SIGGW BPF is further miniaturized. The final area of the stacked SW-SIGGW BPF is only 18.7% of the conventional filter based on normal SIGGW without slow wave and stacked structure, which is very competitive for the room-limited applications. A prototype of the stacked SW-SIGGW BPF with 5.4% and 7.4% fractional bandwidths at 11.8 and 18 GHz is fabricated and measured. A good agreement between the measured and simulated results verifies the validity of the miniaturized design of SW-SIGGW BPF.

In this letter, a compact bandpass filtering power divider with tunable bandwidth based on spoof surface plasmon polaritons (SSPPs) and substrate integrated waveguide (SIW) is proposed. The hybrid-SIW-SSPP structure shows good potential to expand the scope of bandwidth control of the device. The bandwidth can be designed in a wide range by simply optimizing its dimensions or loading interdigital structures (ISs). Defected ground structure (DGS) is also introduced on the bottom layer to further improve the out-of-band suppression. And good isolation can be obtained via additional resistors welded across the SSPP slot. A prototype loaded with dumbbell-shape DGS and two resistors is fabricated with an overall size of 45 mm x 18 mm x 0.5 mm. Both $S_{21}$ and $S_{31}$ are around -3.8 dB within the whole X-band. The simulated and measured results agree with each other well.

In this paper, a plasmonic solar cell using silver nanoparticles is presented. The unit cell structure composes of two layers, each containing a silver nanoparticle deposited on the absorber layer and covered with an indium tin oxide layer. Nanoparticle structure has been used for light-trapping to increase the absorption of plasmonic solar cells. By various light trapping techniques, light can be concentrated in a thin absorber layer. As it will be clarified, through varying the geometry of these nanoparticle structures, the absorption peaks can be directed. All simulation data are obtained using the finite element method. The proposed model achieves two absorption peaks existing at 1.07 μm and 1.17 μm, each with absorptions of around 50%. The parameters of optimized performance have been specified. The results indicate that this model shows an absorption full width at half maximum, reaching 122 nm. Moreover, it can be noticed that the absorption peak can be increased to reach 0.5. The proposed structure has potential applications in the absorption of the infra-red part of the solar spectrum.

The concept of back-contact device architecture for perovskite solar cells (PSCs) is a promising alternative to PSCs with the traditional sandwich-type device architecture. The most convenient and low cost method to fabricate back-contact electrodes for PSCs is using microsphere lithography as it can be performed without expensive photolithography tools and cleanroom environment. Deposition of a monolayer of polystyrene microbeads on the surface of cathode substrates (conductive transparent oxide glass substrates covered with a thin layer of SnO2) is achieved through a self-assembly process. The self-assembly process is based on electrostatic attraction forces between negatively charged microbeads and the positively charged cathode surface. The self-assembled monolayer of polystyrene microbeads is used as a sacrificial polymer mask to fabricate the anode layer on top of cathodes. The back-contact electrodes are obtained after removing the sacrificial polymer mask through a lift-off process.

Issues of amorphous oxide semiconductors (AOSs) thin-film transistors (TFTs) mainly focus on improving electrical performance and stability. Currently, the hump, the abnormal transfer characteristic, is also an essential factor of AOSs TFT. The hump phenomenon was observed for AOS-TFTs with a metal capping (MC) layer under various measurement conditions. The mobility in the MC TFT was improved from 14.8 cm2/Vs to 19.2 cm2/Vs compared to that of the conventional TFTs. The improved electrical characteristics in the MC structure are representative of the carrier injection effect and the change of the current path. This reason reveals that the MC structure has a hump phenomenon under the low drain to source voltage ( $V_{DS}$ ). The hump characteristic does not significantly affect the overall MC TFT characteristics (transfer characteristic, improved electrical characteristics through MC structure, etc.). In addition, it was confirmed that it exhibits very stable hump characteristics through repeated measurements and uniformity. It was found that two current paths are formed mainly due to carrier injection from the metal capping layer in the hump phenomenon observed at low $V_{DS}$ . These divided current paths can lead to two on-currents ( $I_{on}$ ) in the transfer curve. Many studies have recently been conducted to fabricate semiconductor devices with multi-values such as 0, 1, and 2. This divided current path could propose a simple method to achieve multi-values with an easy process.

A thin intrinsic hydrogenated amorphous silicon carbide ((i) a-SiCx:H) layer with a wide band gap attracts attention as an alternative passivation layer instead of intrinsic hydrogenated amorphous silicon ((i) a-Si:H) for heterojunction photovoltaic applications. The optical band gap of (i) a-SiCx:H can be widened up to 2.24eV. An increase in the optical band gap makes this layer appropriate as the window material by reducing the parasitic absorption. However, the deposition regime should be investigated to understand the incorporation of carbon. The influence of several deposition parameters such as precursor gasses flow rates and plasma power density on the (i) a-SiCx:H layers were investigated in optical, electrical, and elemental aspects. Relatively high interface trap densities were detected related to carbon piling up at the interface. An increase in the amount of C in the interface affected the passivation quality and fixed charge density of the layer. The ratio of secondary ion intensities measured by time of flight-secondary ion mass spectroscopy presents general hydrogen filling of possible dangling bonds and the bonding preferentiality between the silicon or carbon atoms. The passivation quality of the (i) a-SiCx:H layer partially enhanced by stack layer deposition of (i) a-Si:H/(i) a-SiCx:H resulting effective lifetime above 100 μs.

In this work, we experimentally investigate the effects of electric bias on the degradation of few-layer MoS2 back-gated field-effect transistors in ambient air. The devices were fabricated using mechanically exfoliated MoS2 flakes, which were transferred to a Si/SiO2 substrate by a PDMS-based transfer. We report an accelerated electric bias-induced degradation of the devices under investigation and used optical and scanning electron microscopy (SEM) to monitor changes of the morphology of the MoS2 channel. In particular, we found a linear dependency of the degradation on the electric field between the Ti/Au source and drain contacts. In addition, we identify four regions in which morphological changes occur, of which the edges of the MoS2 channel are most affected.

Silicon carbide (SiC), a non-oxide ceramic with superior thermo-mechanical stability, chemical and radiation resistive properties, finds extensive utilization in optical instruments for terrestrial and space applications. However, its inherent porous texture (α-HCP) becomes a deterrent for high-performance optical telescopes, although several techniques of surface alterations over sintered or reaction-bonded SiC are available. In the present work, the physical vapour deposition (PVD) technique is adopted to deposit a thick (∼5 μm) Silicon dioxide (SiO2) clad layer on a sintered and optically polished SiC (SSiC) substrate. SiO2 clad layer coated SSiC (SDO-SSiC) substrate reduces the surface porosity of SSiC which is found to be suitable for optical mirror application. Finally, an Al based reflective and oxides protective coatings are deposited on SiO2 clad layer to achieve reflective behaviour. The surface figure of 75 nm PV (peak-to-valley) and less than 2 nm surface micro-roughness values are achieved which meets the stringent optical telescope specifications for terrestrial and space applications. The structural and nano-mechanical properties of presently developed SiO2 clad layer-based SiC telescopic mirror have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-Ray Analysis (EDX), atomic force microscopy (AFM), and nanoindentation techniques. The optical properties are investigated by optical profilometry and wavelength based spectrometric (both in visible and infrared ranges) techniques. Finally, space worthiness studies viz., thermo-vacuum, thermal storage, thermal shock and relative humidity tests have been carried out successfully. The process of cleaning, grinding and polishing at each substrate preparation stage and coatings are also reported comprehensively.

Flexible printed electronic technology makes it possible to fabricate low-cost digital microfluidic (DMF) chips. Inkjet printing on flexible substrates is one of the most cost-effective fabrication processes for DMF chips. Based on inkjet printing technology and simplified coating methods of dielectric and hydrophobic layers, we fabricated low-cost flexible DMF chips (FDMFCs) on PET sheet and on matte photo paper. The surface quality, conductivity and spatial output resolution of the silver lines under different number of printings, different line widths and line gaps on the two types of FDMFCs were comprehensively analyzed. The traditional square dispensing electrodes were optimized to reduce the volume error of the droplets generated during the repeated dispensing operations. Droplets can be driven to implement all the operations on various configurations of FDMFCs by electrowetting-on-dielectric, including closed configuration, open configuration, hybrid configuration composed of closed and open regions on a single chip, and open curved configuration, which are defined as full-range droplet actuation. The droplet motion between closed and open regions in two position modes of the top plate was deeply studied. Droplet operation experiments prove that the motion performance of droplets can be comparable to that of chips processed by traditional technology, and the rapid prototyping technology of the FDMFCs can make the performance of droplet operation mainly depend on the conductivity of the electrode layer and the electrode gap and greatly weaken the influence of the substrate surface quality on the FDMFCs.

In this study, resistive random-access memory (RRAM)-based crossbar arrays with a memristor W/TiO2/HfO2/TaN structure were fabricated through atomic layer deposition (ALD) to investigate synaptic plasticity and resistive switching (RS) characteristics for bioinspired neuromorphic computing. X-ray photoelectron spectroscopy (XPS) was employed to explore oxygen vacancy concentrations in bilayer TiO2/HfO2 films. Gaussian fitting for O1s peaks confirmed that the HfO2 layer contained a larger number of oxygen vacancies than the TiO2 layer. In addition, HfO2 had lower Gibbs free energy (ΔG°=-1010.8 kJ/mol) than the TiO2 layer (ΔG°=-924.0 kJ/mol), resulting in more oxygen vacancies in the HfO2 layer. XPS results and ΔG° magnitudes confirmed that formation/disruption of oxygen-based conductive filaments took place in the TiO2 layer. The W/TiO2/HfO2/TaN memristive device exhibited excellent and repeatable RS characteristics, including superb 103 dc switching cycles, outstanding 107 pulse endurance, and high-thermal stability (104 s at 125 °C) important for digital computing systems. Furthermore, some essential biological synaptic characteristics such as potentiation-depression plasticity, paired-pulse facilitation (PPF), and spike-timing-dependent plasticity (STDP, asymmetric Hebbian and asymmetric anti-Hebbian) were successfully mimicked herein using the crossbar-array memristive device. Based on experimental results, a migration and diffusion of oxygen vacancy based physical model is proposed to describe the synaptic plasticity and RS mechanism. This study demonstrates that the proposed W/TiO2/HfO2/TaN memristor crossbar-array has a significant potential for applications in non-volatile memory (NVM) and bioinspired neuromorphic systems.

With increasing demands for microchips and increasing needs in the nano-scale semiconductor manufacturing industry, atomic layer etching (ALE) has been developing into a critical etching process. Unlike its counterpart in the film deposition domain, atomic layer deposition (ALD), which has been extensively studied, ALE has not been fully studied yet from a modeling and operation point of view. Therefore, this work develops microscopic models to characterize the thermal ALE process of aluminum oxide thin films with two precursors (hydrogen fluoride and trimethylaluminum). First, the reaction mechanisms for the two half-cycles for the thermal ALE process are established. Electronically predicted geometries of the Al2O3 structure with two precursors are optimized. Along with the optimized geometries, possible reaction pathways are proposed and calculated by density functional theory (DFT)-based electronic structure calculations. The proposed reaction paths and their kinetic parameters are used in a kinetic Monte Carlo (kMC) algorithm, which is capable of capturing the features of the thermal ALE of aluminum oxide. The kMC simulation provides an etch time for the given steady-state operating conditions, which are validated via comparison with available experimental results. Finally, data sets collected from the kMC simulation are used to train a feed-forward artificial neural network (FNN) model. The trained FNN model accurately predicts an etch time and dramatically reduces the computation time compared to the kMC simulation, thereby making it possible to carry out real-time, model-based operational parameter calculations. In addition, the trained FNN model can be used to establish a feasible range of operating conditions without demanding experimental work.

This paper presents the use of AZTS, a non-toxic and earth abundant material as buffer layer in CZTS solar cells due to its good lattice match. We have performed simulation on the experimentally fabricated AZTS/CZTS hetero-junction device by adding CZTS as back surface field (BSF) layer. In this work, first we have reconstructed the AZTS/CZTS experimentally designed solar cell then BSF layer is added to boost the solar cell performance in SCAPS simulator. Several parametersof AZTS buffer layer such as generation/recombination rate and doping concentration are varied during simulationto enhance the performance of investigated solar cells structures. It has been noticed that addition ofBSF layer increasesthe efficiency of AZTS/CZTS solar cell from 4.51% to 5.05% along with improvement of both Voc and FF.

In this letter, a threshold switching (TS) selector with Ag doping-based nano-polycrystalline ZnO switching layer (SL) having (002) preferred orientation has been manifested, without incorporating an active Ag metal layer, using a facile co-sputtering deposition technique. The TS selectors with extremely controlled doping of ~0.14 at. % Ag concentration showed remarkable electroforming (EF)-free selection behavior such as gigantic selectivity (~1011), extreme-low off-current (~10 fA), high on-current density (~1.6 MA/cm2), ultra-steep switching slope (~0.8 mV/decade), satisfactory endurance (>106), fast switch-on speed (~38 ns) and relaxation speed (~64 ns), and high device yield (~90%). Furthermore, selector devices showed reproducible selection behavior with stable threshold voltage (Vth) having merely 8% variances.

Interface recombination is one of the factors limiting the performance of Cu(In,Ga)Se_2 (CIGS). Especially in the absence of band grading at the front and rear surface, interface passivation approaches become important to improve device performance. The integration of an oxide layer as passivation layer at the front surface of the CIGS requires meticulous considerations in order not to impact the further steps of the solar cell production. In this article, a novel approach is reported to try to tackle the problem of interface recombination at the front surface of CIGS without affecting further solar cell production steps. In this approach, an Al_2O_3/HfO_2 multi-stack layer with contact openings is applied. NaCl template patterning with preliminarily selected parameters was used to create a homogeneous pattern of contact opening on the CIGS surface and allow the current flow in the device. After the removal of the NaCl islands, the holes in the multi-stack (openings) were visualized by scanning electron microscopy. In addition, energy-dispersive X-ray spectroscopy (EDS) was performed before and after chemical bath deposition of the buffer layer. The EDS result confirmed that the undesired etching of the Al_2O_3 layer during buffer layer deposition was prevented by using a thin HfO_2 layer. Solar cells were produced by using preliminarily selected parameters for the multi-stack design. As a result, without having a significant negative impact on the solar cell parameters, a device design was achieved which is almost comparable with the reference device. In addition, options for future improvement and development are discussed. European Union's H2020 Research and Innovation Program [715027]

Antimony selenide (Sb2Se3) is a promising light absorber material for solar cells because of its superior photovoltaic properties. However, the current performance of the Sb2Se3 solar cell is much lower than its theoretical value (∼32%) due to its low open-circuit voltage (VOC). In this paper, we have demonstrated inorganic vanadium oxides (VOx) as a hole transport layer (HTL) for Sb2Se3 solar cells to enhance efficiency through the VOC improvement. Here, a solution-processed VOx through the decomposition of the triisopropoxyvanadium (V) oxide is deposited on the Sb2Se3 absorber layer prepared by close-spaced sublimation (CSS). With VOx HTL, the built-in voltage (Vbi) is significantly increased, leading to improved VOC for the Sb2Se3 solar cell devices. As a result, the efficiency of the device increases from an average efficiency of 5.5% to 6.3% with the VOx.

In this work, we report high-performance amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with atomic layer deposited Al₂O₃ dielectric processed at a minimal temperature of 189.6 °C via microwave annealing (MWA). The a-IGZO TFT with MWA exhibits an improvement of 57% in subthreshold swing (SS) compared with the unannealed device; meanwhile, it retains high field-effect mobility of up to 29.2 cm²/(V · s) and large switching ratio of >10⁸. Moreover, the SS of the device was further reduced through a two-step MWA treatment. It is believed that MWA treatment effectively reduces the density of trap states associated with oxygen vacancies, promotes the formation of lattice oxygen, and thus improves the quality of IGZO film. MWA with low thermal budget shows great potential in applications of the back-end of line (BEOL)-compatible oxide devices.

Cu(In,Ga)Se2 (CIGS) is a prevalent material with superior thermo-chemical stability and excellent optoelectronic properties for solar cell applications. In thin film form, CIGS could be a potentially economical and building integrated photovoltaic adaptable substitute to Silicon solar cells, solving humanity's extensive energy demands. To be economically sustainable, CIGS thin film processing must be abridged and affordable. We explored a low-cost, simplified wet chemical nano-ink method to make the CIGS thin film absorber layer comprising precursor thin film preparation by spraying CIGS nano-ink and subsequent post-treatment using Selenium vapor under Nitrogen atmosphere at a temperature of 550 °C. The spray-casted nanocrystalline layers were selenized at a low pressure of 1 Torr or 1 atm Nitrogen utilizing elemental pallets of Selenium as a source of Se vapor. The impact of Selenization pressure on the structure, morphology, composition, and electronic conductivity of selenized CIGS thin films absorber is investigated in this study, as well as the device performance associated with the processing parameters.

Sb2Se3, a quasi-1D structured binary chalcogenide, has great potential as a solar cell light absorber owing to its anisotropic carrier transport and benign grain boundaries when the absorber layer is properly aligned along the [hk1] direction perpendicular to the substrate. A growth technique with a high deposition rate, such as vapor transport deposition, is preferred to form an [hk1]-oriented Sb2Se3 film. However, the possible decomposition of Sb2Se3 during cooling after the high-temperature deposition appears to result in Se deficiency accompanied by the formation of deep-level donor-like defects, such as Se vacancies and Sb on Se antisite defects. Here, we present comprehensive passivation strategies for the rear interface of Sb2Se3 solar cells in a superstrate configuration, namely post-deposition annealing treatment (PAT) under Se, and the introduction of an electron-blocking layer between Sb2Se3 and the rear metal contact. The PAT effectively passivated the defects associated with Se deficiency and greatly improved the open-circuit voltage and fill factor of Sb2Se3 solar cells. With the further introduction of a poly(N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine) electron-blocking layer, the Sb2Se3 solar cell achieved an efficiency of 7.0%.

We have studied the effects of proton irradiation on the AlGaN/GaN HEMTs with AlN buffer layer as well as conventional GaN buffer layer. It was found that a short time proton irradiation (~ 50 sec) can promote beneficial effects on device performances, which results in great reduction in the off-state leakage current and the gate leakage current without degrading the output current and transconductance. The pulsed I-V measurement demonstrated that both devices exhibit greatly improved current dispersion characteristics and, particularly, the device with AlN buffer layer shows stronger radiation hardness than that of the device with GaN buffer layer. These interesting results are believed to be due to the hydrogen passivation with thermal annealing effect during the proton irradiation. It is expected that the proper irradiation condition such as fluence, energy, and time is crucial to improve the device performances, rather than to deteriorate the performances.

Here, we report on the progress of our work on fabrication of simple metal–semiconductor-metal perovskite solar cells, in which the metal electrodes directly contact the perovskite layer to create Schottky junction solar cells. The photovoltaic properties of the device strongly depend on the asymmetry in work function values of two metal contacts, which are gold back-contact electrode and silver nanowires percolation network. Modified polyol synthesis was used to produce silver nanowires. To achieve homogeneous, uniform and highly-conductive network formed by silver nanowires on the perovskite layer, various fabrication protocols (deposition technique, ambience, solvent, volume, etc.) have been tested. We have developed several protocols for obtaining silver nanowires network-based electrodes deposited on top of thin perovskite films on glass substrates with the sheet resistances of the silver nanowires network as small as ∼ 2 KΩ/□.

Cu2ZnSnS4 (CZTS) is a good candidate for cost-effective perovskite solar cells (PSCs) due to its direct bandgap with a value of 1.4–1.5 eV. In this study, we investigate CZTS ink as an inorganic hole-transport-layer (HTL) in CsMAFAPbIBr mixed halide PSCs. We study the cell efficiency and hole extraction from the perovskite layer for different thicknesses of HTL. The optimized device exhibits better hole selectivity, and the best efficiency of the device (12.84%) is achieved for the CZTS layer with a thickness of 159 nm. The prepared samples were also tested by open-circuit voltage decay analysis and electrochemical impedance spectroscopies. Results show that the optimized device effectively prohibits the electrons-holes recombination with a charge transfer resistance of 9.38 Ω cm2. This work suggests that the optimal thickness of CZTS as an HTL in triple-cation PSC is about 159 nm by giving short-circuit current density of 23.69 mA cm−2.

In the conventional sandwich structure of perovskite solar cells (PSCs) with the metallic electrodes, the parasitic absorption losses due to the presence of glass substrate, conductive metal oxides and other functional layers below the perovskite film reduce a certain portion of photons that can be harvested by the perovskite absorber. The carbon quantum dots (CQDs) with down-converting properties can absorb high-energy UV light and convert them into the photons with lower energy lying in the visible light region. The CQDs can be used to enhance the light harvesting power of the PSCs so that the negative effect due to the parasitic absorption can be suppressed. In this work, a coating layer composed of CQDs is deposited on the illuminated side of the glass substrate. In contrast to our previous report, the deionized water (DIW) is used to disperse the CQDs instead of dispersing CQDs in the matrix of PMMA and chlorobenzene (CB). By using the new approach, the preparation of CQD coatings is more efficient and the use of toxic CB can be avoided. After systematic optimization of the preparation parameters, it is found that using water as the dispersion medium for CQDs can also yield the effective coatings for PSCs to enhance their light absorption power.

In this paper, several computer simulations have been carried out using lumerical FTDT software. As a result, the optimal layer thicknesses for antireflection coatings SiC/MgF2 and SiC/ZnO/MgF2 deposited on the surface of polished silicon were determined. Among the considered coatings, the double layer structure SiC (60 nm) + MgF2 (110 nm) has the lowest reflection (

In this letter, we demonstrated an approach to introduce a positive shift in transfer curves of lateral metal-oxide-semiconductor field-effect transistors (MOSFETs) on 4H-SiC (0001), without deterioration of channel conductance. With an additional Al2O3 thin film on thermally grown SiO2 after the nitridation process, a dipole layer was formed at the Al2O3/SiO2 interface, which induced the positive shift of flat-band voltage. The field-effect mobility of MOSFET was not changed after the Al2O3 fabrication process, which means that the quality of the nitrogen-passivated SiO2/SiC interface was not damaged by this process.

This article reports a systematic study on the effects of the epitaxial layer structure on the electrical characteristics of AlGaN/GaN high electron mobility transistors (HEMTs) fabricated on freestanding GaN substrates. First, GaN-on-GaN HEMTs were fabricated comprising channel and buffer layers unintentionally doped with Fe atoms those were diffused from the substrate. Their electrical characteristics were compared with GaN-on-SiC HEMTs. The tradeoff relation between maximum drain current and the breakdown characteristics was improved in GaN-on-GaN devices than in GaN-on-SiC devices. A small current collapse was observed in GaN-on-GaN devices despite a high Fe density in the channel. This suggested an influence of Fe diffusion on the frequency dispersion to be comparatively limited. Second, GaN-on-GaN HEMTs were fabricated using a thin undoped channel layer grown on Fe-doped GaN substrate directly or through an Fe diffusion stopper layer. Without the stopper layer, the buffer leakage was significantly increased by reducing the channel thickness, and a 100-nm-thick channel device showed nonpinch-off characteristics. On the other hand, samples with the stopper layer exhibited no buffer leakage and a complete pinchoff up to 200 V. In addition, a sample with an intentional C doping to the buffer layer showed a relatively large current collapse, suggesting a major contribution of C-doping to the frequency dispersion of GaN-on-GaN HEMTs.

Due to the scarcity of indium (In) in the earth and its potential harm to individuals, the development of In-free transparent conductive film is considered crucial. In this work, In-free SnO2:Sb/Au/SnO2:Sb (ATO/Au/ATO, SAS) tri-layer films with high transparency and conductivity were successfully prepared on polycarbonate (PC) substrates by RF and DC magnetron sputtering at room temperature. The influence of the Au layer thickness on microstructure, electrical and optical performances was systematically studied after fixing the ATO thickness to 50 nm. It was indicated by X-ray diffraction patterns that ATO is amorphous and Au is oriented along (111). The trend of increasing and then decreasing light transmission with Au layer thickness was observed in both experimental and simulation results. The improved figure of merit (FoM, 1.89 × 10−2 Ω−1) was achieved in SAS tri-layer film, the resistivity and average transmittance of which was lowered to 7.50 × 10−5 Ω cm and 81.4%, respectively, when Au layer thickness is 11 nm. Moreover, the mechanism of the variation of optical and electrical properties at different Au layer thickness was proposed. Particularly, the SAS tri-layer films also exhibit superior flexibility, durability and adhesion. These results demonstrate SAS tri-layer films are promising alternative to ITO in flexible electronics applications.

Past few decades, nanostructures are useful in the active region and light-harvesting layers in thin film solar cells. In this work, the high reflectance alternative Si/SiO2 distributed Bragg reflectors (DBRs), and aluminum (Al) thin film layers were integrated as a backside reflectors in ultrathin film silicon solar cells to improve the light trapping mechanism using finite-difference time-domain (FDTD) method. DBR is known as one-dimensional photonic crystal (1DPC) used as backside reflectors with the addition of SiO2 buffer layer. Further, the transverse electric (TE) and magnetic (TM) field distribution shown the strong light scattering in the silicon active layer region by integration of top (ITO) and bottom (Al) nanogratings. Both polarization conditions yielded the highest current density (Jsc) of 22.03 (TE) and 30.42 mA/cm2 (TM) achieved within 50 nm active region thickness.

Flexible supercapacitors with high areal energy density are promising energy storage devices to meet the increasing demands for wearable and portable electronic products. Herein, three kinds of flexible electrodes were fabricated electrochemically through tuning spatial distribution of graphene sheets composited with polyaniline (PANi) nanofiber array on carbon cloth, in which graphene sheets were used as the efficient growing substrate or protecting layer for the arrays and directly inserted into the arrays. It is found that the charge storage ability of all the PANi arrays could be enhanced significantly that depended greatly on the spatial distribution of graphene sheets composited with the array. The composite electrodes composing of graphene inserted PANi array on the graphene covered carbon cloth possesses the highest areal energy density among all the electrodes. More clearly, the corresponding all−solid−state supercapacitor devices can reach outstanding performances with a maximum energy density of 313 μWh cm−2 and capacitance retention of 92.7% after 5000 cycles could be achieved in the electrolyte containing Fe3+. This work is believed to provide a new thought for fabricating cost–effective and flexible electrodes with ultrahigh areal energy density, excellent flexibility and cycle stability endow for high−energy wearable/portable energy storage devices.

This letter reports the successful demonstration of large-current and high-voltage (001) vertical-type two-dimensional hole gas (2DHG) diamond trench metal-oxide-semiconductor field-effect transistors (MOSFETs) with a p--drift layer. The fabricated transistor demonstrated a maximum drain current density of 210 mA/mm, a field-effect-mobility of 61 cm2V-1s-1, and a specific on-resistance of 23 mΩ cm2. Moreover, a high breakdown voltage of 580 V with a gate-drain length of 10 μm was obtained, which is the highest value reported for a vertical-type diamond MOSFET to date. These characteristics indicate that a vertical-type diamond MOSFET using a p--drift layer may be used to realize a pchannel power device with a high breakdown voltage and low on-resistance.

Vacuum-air-shift causes trouble to conventional electron beam evaporation (EBE) coatings. This study compares the protection effect of ion assistance and the ALD (atomic layer deposition) Al2O3 capping layer. The vacuum-air-shift was reproduced on an EBE Ta2O5 single-layer film, a Ta2O5/SiO2 double-layer coating, and a high-reflectance mirror. Similar samples were prepared by EBE assisted with ion beam bombardment. Part of the as-deposited coatings were capped by ALD Al2O3 film with a thickness of about 100 nm. The vacuum-air-shift of the samples was tested with an in-situ spectrophotometer. The cross-section of the coatings was imaged by a scanning electron microscope. The ion assistance was found to reduce the vacuum-air-shift to a limit extent, while the ALD capping film was found to eliminate the vacuum-air-shift. The mechanism of the two protection techniques was analyzed, and their usage was compared and discussed. The ALD capping technique may be used in high precision EBE coatings with convenience and low cost.

Heterojunction c-Si and hydrogenated amorphous silicon (a-Si:H) devices with intrinsic a-Si:H thin layer, known as HIT solar cells, are promising alternatives to conventional c-Si solar cells for the possibility of higher open circuit voltage, low temperature processing and lower costs. We have studied the influence of the properties of p-a-Si:H layer and the work function of the front electrode material on the performance parameters of n-c-Si based HIT solar cells using numerical simulation. The findings are further analyzed using energy band diagrams and carrier concentration profiles at the heterointerface of a-Si:H/n-c-Si to reveal the underlying charge transport mechanisms.

Tantalum nitride (Ta3N5) is a very promising photoanode material due to its narrow band gap (2.1 eV) and suitable band alignment for solar water splitting. However, it suffers from severe photocorrosion during water oxidation. In this work, it was found that surface passivation by AlOx and TiOx layers results in dramatically different PEC performance of Ta3N5 photoanode for water oxidation. The mechanism study indicates that the negative charges on AlOx can generate additional field to promote separation of photogenerated charges, while the positive charges on TiOx layer show the opposite effect. As a result, the Ta3N5 based photoanode modified with AlOx layer gives a high photocurrent of 12.5 mA cm−2 for 24 h at 1.23 V versus the reversible hydrogen electrode (RHE). Dynamic analysis implies that the hole extraction and transfer are significantly improved by the modification with the AlOx layer. This work reveals the importance of the charges on surface passivation layer in interface engineering of photoelectrodes.

We report the design and development of vertical 1.5 kV GaN p–n diodes that consists of an 8 μm drift layer and a thin p-GaN/p+-GaN layer grown by metal–organic chemical vapor deposition (MOCVD) on a hydride vapor phase epitaxy (HVPE) synthesized GaN substrate. The drift layer has a low doping concentration of ∼9 × 1015 cm−3 and electron mobility ~ 1200 cm2/Vs at room temperature. The fabricated devices with an optimized guard ring design as edge termination exhibit a breakdown voltage of > 1.5 kV with specific on-resistance of ~ 1.5 mΩ cm2. The breakdown efficiency of these diodes is over 72% when compared to ideal analytical calculations and over 90% with respect to numerical simulations. Temperature-dependent measurements show that the devices have a positive temperature coefficient suggesting the avalanche breakdown mechanism. These results suggest that these MOCVD grown vertical GaN-on-GaN (HVPE) p–n diodes are promising for low-mid range voltage power switching applications.

Radio frequency identification (RFID) is a well-established technology utilized in inventory management, security, logistics, product marketing as well as next generation smart flexible sensor platforms. This work reports the development of printed, wearable graphene temperature sensor on flexible textile substrates with structural configuration of RFID coil. Patterning of graphene in the form of sensing RFID coils on textile surfaces was achieved with cost-effective and scalable spray printing of graphene oxide and sequential reduction to reduced graphene oxide. Graphene RFID coil operating at 13.56 MHz with temperature sensing capability, are printed on flexible, ordinary fabrics to enable wearable and flexible electronics applications. The demonstration of reduced graphene oxide on textile as temperature sensitive layer is the distinct feature of this work. Good sensitivity of 0.0125 degrees C-1 is achieved with linear response in the range of 25 degrees C to 45 degrees C and similar to 12 % decrease in resistance was observed over the measured temperature span. Induced voltage of 100 mV peak-to-peak at an area of 30.25 cm(-2) is measured. RFID performance of the sensor coil under different bending radii starting from fully flat (0 degrees) to complete bending (90 degrees) was also studied, showing that sensor coil performs well during flat operation (100 mV) and stays above noise floor even under fully bended condition (12 mV). Finally, flexible temperature sensing RFID antenna attached to human body to investigate performance for wearable applications, indicating that the sensor can effectively monitor temperatures in the range of 25 degrees C to 45 degrees C.

Eight level resistance switching in a tri-layer ReRAM cell (ZrOx/AlOx/HfOx) of fixed stack thickness was obtained by tuning the spatial location of its intermediate AlOx layer hence by varying its spatial distribution of three dielectrics. Here we have investigated the underlying reason behind the observed well separated low power resistance switching in this type of valance change memory (VCM) cell achieved by varying its SET current compliance and discussed stack design aspect which impacts its characteristics. Electrical characteristics of a favorable cell obtained by our scheme demonstrate non-overlapped and retainable resistance levels even followed by dc endurance cycles. 106 SET/RESET cycle-based ac-endurance measurement was furthermore performed to assess resistance margin between the HRS and the LRS, and favorable cell exhibited well behaved cell-to-cell and cycle-to-cycle variabilities of its resistance states. Furthermore, retention measurements conducted at room temperature and at 85∘C demonstrate stable non-overlapped resistance levels as suitable for the multi-level/cell storage. SET bias scaling of the favorable cell has been finally assessed by numerical simulation.