Showing papers in "Micro and nanostructures in 2022"

Optoelectronic and magnetic properties of transition metals adsorbed Pd2Se3 monolayer

Abstract: In this article, the optical, magnetic, and electronic of pristine and transition metals (TM) adsorbed Pd 2 Se 3 were systematically researched by density functional theory. The results reveal that the most stable position of Pd 2 Se 3 monolayer adsorbed by various TM is different. The band structures of Au-, Cu- and Sc–Pd 2 Se 3 structures demonstrate nonmagnetic metal behaviour, while the Co- and Cr–Pd 2 Se 3 structures display magnetic metal properties. Meanwhile, the Ni- and Pt–Pd 2 Se 3 systems show nonmagnetic semiconductor character, and Fe- and Mn–Pd 2 Se 3 systems exhibit magnetic semiconductor features. Moreover, the work function of Au-, Cu-, Co-, Mn- and Fe–Pd 2 Se 3 structures is lower than Pd 2 Se 3 monolayer, which demonstrates that these structures have good electron emission characteristics. Interestingly, after the adsorption of TM atom, the light absorption of Pd 2 Se 3 system in various regions is boosted to varying degrees, indicating that the introduction of TM atom can improve the light absorption of Pd 2 Se 3 system in ultraviolet, visible and infrared regions. Therefore, it demonstrates that TM-Pd 2 Se 3 systems can be used to fabricate spintronic, photocatalysts and optoelectronic devices. • The most stable positions of Pd 2 Se 3 adsorbed by various TM are different. • The Ni- and Pt–Pd 2 Se 3 systems show nonmagnetic semiconductor character, and Fe- and Mn–Pd 2 Se 3 systems exhibit magnetic semiconductor. • The work function of Au-, Cu-, Co-, Mn- and Fe–Pd 2 Se 3 structures is lower than that of Pd 2 Se 3 . • The introduction of TM atom can improve the light absorption of Pd 2 Se 3 system in ultraviolet, visible and infrared regions.

Performance enhancement of (FAPbI3)1-x(MAPbBr3)x perovskite solar cell with an optimized design

Abstract: In this paper, an optimized design of (FAPbI3)1-x(MAPbBr3)x perovskite solar cell is numerically investigated using SCAPS-1D software package. A variety of potential charge transport materials are investigated. Cu2O as HTL and ZnO as ETL outperform other choices; they are therefore considered as the best candidates. The impact of the electronic properties of both ZnO/perovskite and Perovskite/Cu2O interfaces on the solar cell performance is thoroughly investigated. We discovered that appropriate values of the conduction band offset (CBO+ = 0.29) and valence band offset (VBO+ = 0.09) assure a “spike-type” band alignment at both interfaces. This choice lowers the unwanted interfacial recombination mechanism, resulting in a challenging PCE. In addition, the impact of the work function of back contact is also investigated. According to simulation findings, Ni back electrodes with a work function of 5.04 eV is appropriate for Zn0.8Mg0.2O/(FAPbI3)0.85(MAPbB3)0.15/Cu2O perovskite solar cell. The optimized FTO/MgZnO/(FAPbI3)0.85(MAPbBr3)0.15/Cu2O/Ni PSC reaches a conversion efficiency as high as 25.86%. These findings will pave the way for the design of low-cost, high-efficiency solar cells.

Broadband polarization insensitive and tunable terahertz metamaterial perfect absorber based on the graphene disk and square ribbon

Abstract: Designing broadband absorbers with only one metamaterial layer operating in the terahertz band is a relatively difficult challenge. In this paper, we proposed and investigate a broadband metamaterial perfect absorber (MPA) based on the graphene disk and square ribbon. The conductive substrate of this structure is made of gold and the middle dielectric layer of this structure is made of Rogers RT5880LZ, which acts as a spacer layer between the gold and graphene layers. This structure, while having only one metamaterial layer, also has the advantage of easy implementation because the graphene embedded on the dielectric surface does not have a complex design. The simulation results show that the proposed absorber can provide absorption above 90% with a bandwidth of 2.173 ​THz (1.482–3.655 ​THz). The fractional bandwidth ratio of the proposed structure is 85% for absorption greater than 90%. The absorption mechanism of this structure based on electric fields has been investigated. Since the design of the proposed broadband MPA is symmetrical, this structure is not sensitive to polarization and has a good bearing angle in the range of 0–30°. The proposed structure is tunable because we can shift the absorption frequency by changing the Fermi level of graphene (μ c ). The proposed absorber with these properties is suitable and flexible for applications such as sensing, imaging, and spectroscopy. • The structure has the advantage of easy execution due to its single-layer metamaterial and simple design. • The bandwidth of the structure for absorption above 90% is equal to 2.173 ​THz (1.482–3.655 ​THz). • The structure is tunable without the need for structural changes. • The structure has behaviors such as insensitivity to polarization and high tolerance to the incident angle. • The structure is suitable for applications such as sensing, imaging and spectroscopy.

The effects of temperature and pressure on the optical properties of a donor impurity in (In,Ga)N/GaN multilayer cylindrical quantum dots

Abstract: This paper examines the variation of the linear, third-order nonlinear and total intersubband optical absorption (refractive index changes) coefficients of a donor impurity in multilayer cylindrical quantum dots (MCQDs), under the effect of temperature T and hydrostatic pressure P . Moreover, in this study, we also examined the effect of structure parameters on the optical absorption coefficients of the system. The Schrödinger equation describing the system is solved numerically by the finite element method (FEM) within the effective mass approximation. In our calculations, the confinement potential is modeled by a parabolic form in the radial direction and a square one in the z -direction. The optical absorption coefficients and refractive index changes have been investigated versus the quantum dot radius, indium composition and intensity of the incident electromagnetic for three allowed transitions: 1 s - 1 p , 2 s - 1 p and 1 p - 1 d . Our essential outcomes exhibit that the optical absorption coefficients and refractive index changes are strongly sensitive to the variation of quantum dot sizes, which enhance and blueshift as the quantum confinement is strong. On the contrary, the optical absorption coefficients and refractive index changes diminish and redshift as the quantum confinement reduces. • The optical absorption coefficients (ACs) and refractive index changes (RICs) diminish and redshift as the quantum confinement reduces. • The temperature effect reduces the electronic confinement, consequently, the optical ACs and RICs shift to lower energies (red-shift). • The hydrostatic pressure reflects an additional confinement, which makes the ACs and RICs blueshifted.

Performance enhancement of CIGS solar cell with two dimensional MoS2 hole transport layer

Abstract: This paper describes a performance analysis of solar cell based on Cu (In 1-x Ga x )Se 2 (CIGS) material as an absorber layer together with two dimensional (2d)-MoS 2 as hole transport layer (HTL) inserted between absorber layer and back contact using 1D-SCAPS program tool. In this work, numerical modeling tool has used to investigate the effect of thickness, doping concentration and defect variation on the performance of solar cell. Based on optimization of the device parameters, highest power conversion efficiency ( P C E ) of 26.81% ( V o c =0.783 V, J s c = 40.30 mA/cm 2 and F F = 84.97%), has been obtained for ZnO/CdS/CIGS/MoS 2 photovoltaic cell having 1.18eV energy bandgap ( E g ) of CIGS layer. Performance of proposed CIGS solar cell with 2d-MoS 2 HTL is better than the conventional CIGS solar cell and provide new path for recent advanced research for fabrication of solar cell on this technology. Further, solar cell's performance has been analyzed for various series-shunt resistances, work function of metal contacts and temperature for better analysis of the cell. • Optimization of thickness, doping concentration and defect density of CIGS absorber layer. • Power conversion efficiency of proposeddevice ZnO/CdS/CIGS/MoS 2 obtained 26.81%. • Design a cost-effective and thin film CIGS solar cell. • Work function of front and back contact analyzed. • Performance study at various operating temperature and series-shunt resistance.

Recent developments in materials, architectures and processing of AlGaN/GaN HEMTs for future RF and power electronic applications: A critical review

Abstract: This article critically reviews the architectural novelties, emerging materials (substrate, buffer, barrier & contact materials), technological advancements, processing techniques adopted, geometrical influences & challenges during fabrication, and driving reliability aspects of AlGaN/GaN high electron mobility transistors (AG-HEMTs) that are gaining rapid & progressive adoption as a semiconductor device of outrival choice for high power & RF frequency applications, due to exceptional material-properties of the heterostructure. The device has matured in the last decade reaching ID(drain current) up to 1940 mA/mm, gm(transconductance) up to 556 mS/mm, fT(cut-off frequency) up to 200 GHz, fmax (maximum oscillation frequency) up to 308 GHz and Vbr (breakdown voltage) up to 2900 V. The impact of various barrier and buffer materials, contact technologies, annealing process and temperature, passivation and etching techniques on the RF & DC performance of AG-HEMTs is presented in this paper. An assessment of the influence of irradiation effects, underlying degradation mechanisms, and associated reliability aspects is also included, which helps to exploit the potential of AG-HEMTs in space technology. AG-HEMTs stood a step ahead of conventional devices due to their exceptional material properties and enjoy a diverse range of applications like radar, satellite communication, telecommunication, sensors, space and aeronautics, microwave & millimeter-wave devices, and wireless infrastructures and many more.

Binding energy, polarizability, and diamagnetic response of shallow donor impurity in zinc blende GaN quantum dots

Abstract: In this theoretical investigation, the binding energy, the binding energy Stark-shift, the dipole moment, the polarizability, and the diamagnetic susceptibility related with a confined shallow donor impurity in zinc blende GaN conical-shaped quantum dots are calculated under the effect of an electric field applied along the z-direction. Calculations have been made by using a variational approach within the infinite confining potential model and considering the parabolic conduction band and the effective mass approximations. The results suggest important dependencies of the calculated physical properties on the variation of the dot dimensions, axial impurity position, and the intensity of the applied electric field. It is observed that: i) the binding energy Stark shift increases up to a maximum value and then decreases with increasing the strength of the electric field, and it is strongly influenced by the impurity position and geometrical parameters, ii) for a fixed electric field value, the binding energy Stark shift is always an increasing function of the dot height, and iii) for fixed electric field values, the binding energy Stark shift shows a mixed behavior concerning the dot radius, i.e., for low field strength, the binding energy is always a growing function of the radius, and for large field strengths, such physical quantity grows with the radius up to a maximum and then decreases. Furthermore, the electric field (the strong quantum confinement) enhances slightly (diminishes) the diamagnetic susceptibility of impurity.

Design and simulations of 24.7% efficient silicide on oxide-based electrostatically doped (SILO-ED) carrier selective contact PERC solar cell

Abstract: Silicon-based passivated emitter and rear cell (PERC) has emerged as a mainstream high-efficiency cell technology in recent years. However, inherent contact recombination loss becomes the main limiting factor in PERC solar cells, limiting the performance of the PERC device toward higher efficiencies close to the Auger limit of 29.4%. Therefore, carrier selective contacts such as polysilicon on oxide (POLO) have been researched and investigated in the past to mitigate contact-related losses. POLO contacts require a heavily doped polysilicon layer on a thin tunnel oxide layer to facilitate the tunnelling of desired charge carrier electron or hole and simultaneously push the other carrier hole or electron back into the substrate. In this work, single-sided POLO contact-based PERC device is investigated, and an alternative approach is projected to avoid the need for a heavily doped polysilicon layer in carrier selective contacts. Silicide on oxide-based electrostatically doped (SILO-ED) carrier selective contact is designed and examined through extensive device simulation using Silvaco based process and device simulations. Four different devices with a planar or textured surface are designed, such as conventional, single POLO, single POLO with ED, and SILO-ED PERCs to have a comparative analysis. Initially, the influence of surface recombination velocity (SRV) (from 102 to 107 cm/s) on the front surface in the case of a non-POLO PERC device has been investigated. Afterwards, the PERC device by employing single-POLO contact on the front surface has been designed and simulated to obtain 23.95% efficiency. Further, the concept ED is introduced, and 24.6% efficient ED-POLO (with 1 nm thick poly-Si) and 24.7% SILO-ED contact-based PERC devices are designed to avoid the need for a heavily doped polysilicon layer. The SILO-ED-based PERC device with 24.7% conversion efficiency is also compared with the Auger limit (29.4%) for the comparative purpose. The work reported in this research article may pave the way for developing highly efficient PERC solar cells.

First-principles calculations to investigate electronic, structural, optical, and thermoelectric properties of semiconducting double perovskite Ba2YBiO6

Abstract: This paper presents a computational analysis of some physical properties of Ba 2 YBiO 6 double perovskite, using full potential density functional theory (DFT) calculations. Our study demonstrates that the calculated lattice constant agrees well with the experimental one. The electronic structure results show that Ba 2 YBiO 6 is a p-type indirect band-gap semiconductor, with bandgap of 2.87 eV. The optical properties are explored with reflectivity (R ( ω ) ), refractive index (n ( ω ) ), energy loss function ( E l o s s ( ω ) ) , complex dielectric constant ( ε ( ω ) ) , absorption coefficient ( α ( ω ) ), and optical conductivity ( σ ( ω ) ). Furthermore, for thermoelectric response of the material examined with the Seebeck coefficient (S) and the electrical conductivity (σ/ τ ), showed that holes are the majority carriers demonstrating semiconducting nature of the material. These findings suggest that double perovskite Ba 2 YBiO 6 could fit for ultraviolet (UV) and visible-light optoelectronic devices, and thermoelectric applications. • Ba 2 YBiO 6 is a p-type semiconductor with an indirect band gap. • Ground-state properties of the double perovskite Ba 2 YBiO 6 were determined. • A high Spaired with low κ resulted in a high ZT near to unity. • Ba 2 YBiO 6 fits ultraviolet (UV), visible-light optoelectronic devices, and thermoelectric applications.

Effects of electric field and biaxial strain on the (NO2, NO, O2, and SO2) gas adsorption properties of Sc2CO2 monolayer

Abstract: Herein, we present a first-principles study of the effects of electric field and biaxial strain on the adsorption properties of Sc2CO2 monolayer in respect of O2, SO2, NO, and NO2 gases. We calculated the optimized configuration, adsorption energy, charge transfer, band structure, and densities of states of the adsorption systems under various electric fields and biaxial strains. We found that the adsorption intensities of NO2, NO, O2, and SO2 on the Sc2CO2 monolayer decrease with increasing the positive electric field. However, the electric field of 0.408 ​V/Å is not large enough to cause the desorption of O2, SO2, NO, and NO2 molecules, and it does not change their chemisorption nature on the Sc2CO2 monolayer. On the other hand, the gas adsorption intensity increases with increasing the biaxial strain from −10% to 10%. The Sc2CO2 monolayer with the −10% compressive strain physisorbs NO2, NO, O2, and SO2 molecules as compared to the chemisorption on the pristine one. The biaxial strains ϵ≥2% change the selectivity in gas adsorption of Sc2CO2 monolayer to NO2 molecule, compared with the O2 molecule on the pristine Sc2CO2 monolayer. The present work suggests an effective way to obtain attractive gas adsorption properties of two-dimensional materials using strain engineering for future gas sensors, gas capture or toxic gas filtration applications.

Study on compensation behaviors and hysteresis characteristics of a graphene-like trilayer with sandwich structure

Abstract: This paper focuses on a ferrimagnetic mixed-spin (3/2, 5/2) Ising model with an ABA sandwich structure for a graphene-like trilayer. By means of Monte Carlo method, the compensation behaviors and hysteresis characteristics of the system are investigated induced by different parameters. It is found that the negative increase of crystal field of sublattices a with large spin and its weak exchange coupling are favorable for the compensation behavior. In addition, we also find that the system may exhibit the magnetization plateaus at low temperature and the triple-loop hysteresis phenomenon because of the competition between external magnetic field and various physical parameters. • A ferrimagnetic mixed-spin (3/2, 5/2) Ising model with an ABA sandwich structure was proposed. • The effects of crystal field and exchange coupling were studied. • Magnetization, susceptibility, specific heat and internal energy were discussed. • Phase diagrams of the critical and compensation temperatures were presented. • Interesting magnetization plateaus and multi-loop hysteresis phenomena were found.

Realization of polarization adjusting in reconfigurable graphene-based microstrip antenna by adding leaf-shaped patch

Abstract: In this article, the design of a microstrip leaf-shaped patch antenna based on a semi-metal substance called graphene is studied. Configuration of the antenna is considered in a method that each of the various sections of the antenna dependent on chemical potential variations can make available a specific radiation status for the far-field of the antenna. Basic aspect of the present plan is to regulate the antenna polarization only by variation of the Fermi energy quantity of its graphene layer. In a way as if it's main physical construction stays unchanged. With this idea, it is achieved the possibility of achieving an antenna with an advantageous matching range in the limit of 0.3 through 1 THz, which can control its polarization in three modes (RHCP, LHCP & LP) for the range of 0.5–0.7 THz with the axial ratio less than 3 dB. Remarkably, the physical structure of the antenna produced it feasible for us to attain circular polarization by attaching leaf-shaped layered patches at its edges.

A noticeable improvement in opto-electronic properties of nebulizer sprayed In2S3 thin films for stable-photodetector applications

Abstract: In the present work, the versatile Indium sulfide thin film (In2S3) are deposited on glass substrates by using nebulizer assisted spray pyrolysis technique at 350 °C for ultra violet (UV) light detection application. The effect of the of indium and sulfur molar concentrations on the structure, morphology, optical characteristics, and photo-sensing capability of the prepared In2S3 films were systematically examined in the range of 0.01 M–0.03 M. The structural analysis of the 0.03 M sample showed a maximum crystallite size of 36 nm. The morphological image from the scanning electron microscope showed a homogeneous, large size grained surface of In2S3 completely covering the substrate. As the molar concentration was raised from 0.01 to 0.03 M, the indium to the sulfur ratio in the prepared films ranged from 1.02 to 1.16. All the prepared films showed good absorption in the ultraviolet region of the electromagnetic spectrum. The sample prepared at 0.03 M was found to have a minimum band gap of 2.38 eV and a maximum PL intensity at 680 nm. The I–V characteristics show a photocurrent of 1.4 × 10−5 A under UV light of wavelength 365 nm for an external bias voltage of ±5 V. A maximum responsivity of 2.74 A/W, detectivity of 2.65 × 1010 Jones was exhibited by 0.03 M sample with a high EQE of 63.9%. The prepared In2S3 thin film can be used as active material in photodetectors.

A critical review on performance, reliability, and fabrication challenges in nanosheet FET for future analog/digital IC applications

Abstract: This article critically reviews the fabrication challenges, emerging materials (wafer, high-k oxide, gate metal, channel materials), dimensional influences, thermal effects, growth techniques utilized, performance, and reliability concerns involved in Nanosheet FET. The Nanosheet FET is getting mainstream acceptance in the semiconductor industry due to its outstanding low-power performances. The NSFET is expected to replace the state-of-art FinFET, and Nanowire FET devices in the coming years. With power and performance combined in NSFET, cognitive, edge, and other computing platforms can be delivered via hybrid cloud environments. Keeping this in view, the performance and reliability comparison of all the three devices is assessed. Several aspects such as random discrete dopants (RDD), metal grain granularity (MGG), gate-edge roughness (GER), and line-edge roughness (LER), Bias Thermal Instability (BTI), and Hot Carrier Injection (HCI) influencing the performance of FinFET, NWFET, and NSFET is studied. The effect of strain engineering, surface orientation in NSFET is also studied. The primary reliability concern Self Heating effect (SHE) which is the root cause of device degradation is also assessed. Furthermore, an insight into future advanced devices (Forksheet FET, Complementary FET, Vertical Transport FET) is provided which are still under development that might possibly replace Nanosheet FET is also presented in this paper. • Critically reviews the challenges in fabrication. • Demonstrates the reliability issues, strain engineering, surface orientation, and geometrical influences in NSFET. • Highlights the comparison between state of art devices FinFET, NWFET, and NSFET. • Investigates the future research directions in NSFET. • Highlights the evolution of high mobility channel materials, wafer, high-k oxide, gate metal, thermal effects, and performance of NSFET.

Renovation of dual-band to quad-band polarization-insensitive and wide incident angle perfect absorber based on the extra graphene layer

Abstract: In this article, first, using conventional graphene-dielectric-metal layers, we have achieved a perfect dual-band terahertz absorber. The obtained results indicate that there are two absorption bands of 97.66% and 98.64% ranging in 5.45 and 7 THz, respectively. Then, the electric fields of this structure at the desired frequencies are also shown to understand the absorption mechanism better. Next, due to the symmetry in the structure relative to the center of the shape coordinate, by adding another layer, a nearly perfect quad-band absorber is obtained. Also, this model of structure has four absorption bands with peaks of 84.4%, 95.6%, 99.2% and 96.12% at frequencies of 4.15, 5.14, 5.58 and 7.35 THz, respectively. Usually, in multi-band structures, the average percentage of absorption bands is expressed, which in the proposed structure is 93.83%. Another interesting advantage of the proposed structure is that the absorption rate is insensitive to wave polarization changes. This structure, in addition to insensitive to being polarization, has a wide incident angle too. This structure can be used in sensor, photodetectors and imaging applications due to perfect absorption rates and multi-band capability.

Thermodynamic characteristics and magnetocaloric effect of a diluted graphdiyne monolayer with defects: A Monte Carlo study

Abstract: Based on Monte Carlo simulation, we studied the thermodynamic characteristics and magnetocaloric effect of a diluted graphdiyne monolayer with defects. The changes of magnetization, magnetic susceptibility and internal energy induced by physical parameters were examined. In particular, the effects of crystal field, external magnetic field and defect concentration on magnetic entropy change, adiabatic temperature change and hysteresis behavior were studied in detail. In addition, we also gave the relative cooling power induced by different external magnetic field and defect concentration. Finally, we found that defect concentration, temperature and crystal field have similar effect on hysteresis loops.

Effect and optimization of ZnO layer on the performance of GaInP/GaAs tandem solar cell

Abstract: Two-dimentionnal Atlas SILVACO-TCAD® device simulator is used to simulate the performances of dual-junction (2J) GaInP/GaAs tandem solar cell under AM1.5G illumination spectrum. The structure of GaInP/GaAs tandem solar cell consists of the combination of two single-junctions based on GaInP top-cell and GaAs bottom-cell. The performance of GaInP/GaAs tandem solar cell is studied using ZnO intermediate layer as a transparent conducting oxide (TCO) between the bottom and top cells to connect them in serial structure. An undoped ZnO front layer is used as an anti-reflective (AR) layer in front side of GaInP top-cell to enhance the conversion efficiency. Without ZnO front layer, a conversion efficiency of 25.29% has been achieved with 0.95 μm base layer thickness of GaInP top-cell and a current-matching density for both cells was Jsc = 11.30 mA/cm2. Optimization resulted in record efficiency of 30.82% in GaInP/GaAs tandem solar cell by introducing ZnO front layer with 0.7 μm base layer thickness of GaInP top-cell with a current-matching density of 13.66 mA/cm2 and an open circuit voltage of 2.51 V. The GaInP/GaAs tandem solar cell in current study exhibit an improvement in conversion efficiency using anti-reflective ZnO front layer. This results are a promising step to fabricate an efficient III‐V multi-junctions solar cells.

A rectifying Al/ZnO/pSi/Al heterojunction as a photodiode

Abstract: The investigation reports on fabrication and measurements of heterojunction diode based on ZnO layer. The layers are ultrasonic sprayed onto p-type silicon substrates at 350 ​°C and the front contacts made from aluminum have been thermally evaporated in low pressure vacuum. The Al/ZnO/p-Si/Al device is then made-up and characterized by current-voltage and capacitance-voltage under dark, light and temperature environments. The ideality factor exceeds the unity which confirms the non-ideal comportment of such device based on nZnO layer. An interesting rectifying sketch around 2544 in dark and 4082 in light is recorded as shown by I–V curve. The electrical parameters of such device are determined in dark and light (60–150 ​mW/cm 2 ) conditions displaying the values of ideality factor (n i ) of 3.5 (1.6), barrier height Φ B of 0.74 (0.89) V, series resistance R s of 5 (1.6) kΩ. Influence of temperature on the current-voltage curve is evidenced within the 22–107 ​°C range. To boost this study, the measurement of C–V-f characteristics are measured and interface state densities of ZnO/p-Si diode in dark, light and temperature environments are investigated. Richardson plot evidences numerous parameters of ZnO/pSi heterojunction diode. • Al/ZnO/p-Si/Al heterojunction based on ZnO layers is fabricated by spray pyrolysis process. • I–V characteristics under room temperature in dark, light and under temperatures are measured. • C–V characteristics under room temperature in dark and under low and high frequencies are investigated. • Interface state density properties are also investigated inside the heterojunction. • Such results give to ZnO/Si/Al heterojunction photodiode properties.

Ferric oxide and heterostructure BlueP/MoSe2 nanostructure based SPR sensor using magnetic material nickel for sensitivity enhancements

Abstract: In the present paper, we examine a highly sensitive surface plasmon resonance (SPR) sensor structure based on angular interrogation. Our simulations are based on transfer matrix method (TMM) and a monochromatic light of wavelength 633 ​nm has been used. The SPR configuration designed by the CaF 2 Prism-Ag-Fe 2 O 3 –Ni-BlueP/MoSe 2 -Sensing medium is theoretically analyzed to enhance the performance of the sensor. A monolayer of Fe 2 O 3 sandwiched among the Ag, Ni and BlueP/MoSe 2 layers provides the high sensitivity of 395 0 RIU −1 for the proposed SPR sensor when the refractive index of the sensing medium is 1.330. The proposed SPR sensor has times improved angular sensitivity than a conventional SPR sensor. Monolayers of Ni and BlueP/MoSe 2 have been used as a bio-compatible reagent to enhance the angular sensitivity of proposed SPR sensor. The proposed SPR sensor has the potential to be used in biosensing applications. • For simulation purpose transfer matrix method (TMM) is utilized. • To theoretically analyzed the performance of the SPR sensor “Kretschmann Configuration’’ is selected with CaF 2 Prism-Ag-Fe 2 O 3 –Ni-BlueP/MoSe 2 -Sensing materials. • The optimized sensitivity 395 0 RIU −1 sensor at refractive index 1.330 is achieved for the proposed SPR sensor. • Other performance parameters like Detection accuracy, Quality factor and FWHM, have been also calculated for proposed SPR sensor. • Fe 2 O 3 , Ni and BlueP/MoSe 2 heterostructure have been used to enhance the performance of SPR sensor. • The transverse magnetic field intensity (8.579 ​V/m) and penetration depth (248.85 ​nm) of the proposed SPR sensor have also been achieved. • The proposed SPR sensor has a high potential in the fields of biochemical and biomedical applications.

A graphene based dual-band metamaterial absorber for TE polarized THz wave

Abstract: A graphene based tunable metamaterial perfect absorber is designed, which is a classic and simple sandwich structure composed of a non-rotationally symmetric graphene pattern layer, a TOPAS dielectric layer and a thick enough gold ground plane. The dynamically adjustable absorption property of the proposed absorber is polarization sensitive, which is novel compared with the widely studied polarization insensitive metamaterial absorber. For TE polarized incident electromagnetic waves (EMW), the dual-band absorption can be generated at frequencies of 4.268 THz and 6.032 THz with peak absorption coefficients up to 99.99% and 99.79%, respectively. But for TM light, there is only one near unity absorption band located at about 4.148 THz. So it will have potential application value for the polarization state resolution of THz waves. The research mainly concentrates on the dual-band tunable absorption under TE polarized incident light. The factors affecting the absorption properties of the proposed absorber are studied by discussing the dependence of the geometric parameters as well as chemical potential and relaxation time of the graphene on the absorption. The simulation results are verified by using multiple reflection interference theory (MRIT) and impedance matching theory (IMT), and the results show that the theoretical results match well with the simulation results. The absorber can achieve good absorption performance in a wide range of incident angles for TE light. Furthermore, by selecting two different graphene chemical potential, good performance of THz switching can be realized. In addition, the application in the field of refractive sensing is also investigated in detail, and higher sensitivity and better figure of merit (FOM) can be obtained. Thus, the designed graphene-based dual-band THz metamaterial absorber has great potential in polarization resolution, EMW absorbing, THz switching, refractive index sensing and so on.

Correlation between electrical properties and growth dynamics for Si-doped Al-rich AlGaN grown by metal-organic chemical vapor deposition

Abstract: Correlation between electrical properties and growth dynamics for Si-doped AlGaN with Al mole fraction above 60% has been investigated. It is found that the electron concentration decreases significantly when decreasing the growth rate, while the electron mobility experiences a non-monotonic process of increasing at first and then decreasing. Combination of secondary ion mass spectroscopy and panchromatic cathodoluminescence results, reveals that the evolution of electrical properties mainly originates from compensation of III vacancy (VIII) to Si dopant, making VIII-nSi complexes, i.e., the concentrations of VIII-nSi complexes increase with decreasing the growth rate, implying high growth rate principle is vital for n-AlGaN.

A new pocket-doped NCFET for low power applications: Impact of ferroelectric and oxide thickness on its performance

Abstract: Negative capacitance field-effect transistor (NCFET) is a potential device that has exhibited an immense prospective to outplace conventional FETs because of their steep switching characteristics driven by ferroelectric gate stack. The negative capacitance in ferroelectrics yields a voltage step-up action that curtails the sub-threshold swing (SS) below 60 mV/decade. In this work, a device based on single gate NCFET (SG-NCFET) and a highly doped double pocket double gate (HDDP-DG-NCFET) with n++ pocket at the edge of source and drain channel junction are proposed to investigate the impact of the morphological modification on electrical parameters of NCFET. In addition, the effect of incorporating pocket in HfO2 based single gate and double gate NCFET is investigated that delivers steep SS and enhances the switching ratio. The device architecture is designed systematically to boost ION/IOFF ratio by optimizing the pocket thickness and ferroelectric parameters. Various scaling parameters are optimized to achieve an OFF current of 1.9 × 10−11 A/μm, 2.65 × 10−13 A/μm, ON-OFF current ratio of 108, 1010 and SS of 36.2 mV/decade, 25.5 mV/decade for SG-NCFET and HDDP-DG-NCFET, respectively. Finally, the proposed NCFET characteristics are compared to those of prevailing NCFET designs and the HDDP-DG-NCFET design emerges out to be a better solution for low-power applications.

Synthesis of CZTS kesterite by pH adjustment in order to improve the performance of CZTS thin film for photovoltaic applications

Abstract: Quaternary CZTS (Cu 2 ZnSnS 4 ) kesterite thin layers were successfully made by electrochemical deposition method. CZTS thin layers were deposited on Indium Tin Oxide (ITO) from an aqueous solution. In this work, the effects of pH adjustment under ambient conditions of CZTS thin films were studied. The as grown samples were investigated by numerous existing characterization systems. The X-ray diffraction (XRD) proves the polycrystalline description of the layer. The average crystallite size is varying from 10 ​nm to 24 ​nm of the films is dependent on the pH of the solution. All the thin films are in the CZTS kesterite phase attributed to A 1 mode at 334 ​cm −1 verified by Raman spectroscopy. The SEM and AFM study show that the pH variation of the solution improved the surface morphology and topography of the CZTS thin films which increase several nm in grain size. Moreover, the optical analysis indicates a suitable band gap in the range of 1.5–1.8 ​eV depending upon the sulfurization temperature. It is found that the pH variation affects both the stability and the performance of the high-quality CZTS absorber layer applications. The CZTS layer with 4.80 pH was annealed at 450 ​°C and 500 ​°C, and at these temperatures the band gap was varied. At the end the band gap variations effect on the performance of CZTS based solar cell is being analyzed by using a simulation tool SCAPS-1D. • Quaternary CZTS was prepared via one-stepelectrochemical deposition. • The pH variation make a significant impact on XRD, morphology and grain size. • The solution pH 4.8 exhibit pure kesterite CZTS without any secondary phases. • The optical bandgap was observed between the1.5 ​eV–1.79 ​eV by the effect of sulfurization of CZTS sample having 4.80 pH. • SCAPS-1D software was used to elaborate the bandgap variation.

Polarization-doped quantum wells with graded Al-composition for highly efficient deep ultraviolet light-emitting diodes

Abstract: The efficiency performance of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) suffers from the strong polarization effect in multiple quantum wells (MQWs). Here, we propose V-shaped QWs to improve the quantum efficiency of DUV LEDs. We numerically investigated the effect of QWs with graded Al-composition on the device performance of DUV LEDs. Simulation results show that the QWs with graded Al-composition can mitigate the detrimental factors of traditional QWs with flat Al-composition, such as tilted energy band and separation of carrier wave function. Furthermore, compared to the QWs with linearly decreased or increased Al-composition along the growth direction, the V-shaped QWs can simultaneously alleviate the slope of valance and conduction band and obtain the better carrier confinement ability. Therefore, the DUV LED with V-shaped QWs exhibits a better optical performance.

A detailed review of perovskite solar cells: Introduction, working principle, modelling, fabrication techniques, future challenges

Abstract: Researchers worldwide have been interested in perovskite solar cells (PSCs) due to their exceptional photovoltaic (PV) performance. The PSCs are the next generation of the PV market as they can produce power with performance that is on par with the best silicon solar cells while costing less than silicon solar cells. The efficiency of PSCs has increased from 3.81% to 25.7% within a decade, demonstrating their immense potential. In this review, the advantages of PSCs and the evolution of efficiency with various configuration are summarized and discussed. The manufacture of PSCs on a large scale and the fabrication of perovskite films are described as well. Despite their advantages, PSCs have encountered numerous problems, including toxicity and degradation in the presence of moisture, oxygen, and UV light. Thus, we emphasize this line added to the difficulties preventing the commercialization of PSCs, as well as the road map towards commercialization are thoroughly examined.

Sensitivity of indium molar fraction in InGaN quantum wells for near-UV light-emitting diodes

Abstract: InGaN-based quantum wells (QWs) have higher threading dislocation density (TDD) in InGaN Light-emitting diode (LED). Despite of higher TDD, variation of Indium (In) molar fraction in the QW generate localized excitons with higher Indium composition, thus preventing bound carriers from non-radiative recombination. In this work, the sensitivity of the Indium molar fraction in InGaN QWs is explored for near-ultraviolet (UV) LEDs. The theoretically calculated results show that as the Indium composition increases in InGaN QWs, the radiative recombination increases along with an increase in carrier injection efficiency. The reduced non-radiative recombination for higher Indium composition leads to the enhanced spontaneous emission rate and internal quantum efficiency (IQE). For lowered Indium composition, the peak emission wavelength of the InGaN LEDs shift toward the shorter wavelength and the performances degrade drastically. Hence for shorter UV LEDs, the AlGaN-based device structure should be a suitable choice.

The effect of ZnS buffer layer on Cu2SnS3 (CTS) thin film solar cells performance: Numerical approach

Abstract: The aim of this paper is to optimize a new structure of Cu2SnS3 (CTS) thin-film based solar cells by using the one-dimensional solar cell capacitance simulator (SCAPS 1D). We proposed ZnS as a non-toxic buffer layer and ITO as a window layer, neither of which has been reported with a CTS absorber layer. The effects of various parameters that affect CTS thin-film solar cell performance, such as thickness of the absorber layer, carrier concentration, band gap, and temperature, are investigated. The generation and recombination rates in both structures, Mo/CTS/ZnS/ITO and Mo/CTS/CdS/ITO, are studied. The results reveal that solar cell performance is enhanced within the range of 5e+16–2e+17 cm−3 of carrier concentration and 1.3–1.5 eV of band gap of CdS. The recombination rate at the CTS/ZnS interface is significantly lower compared to the CTS/CdS interface, indicating good conduction band alignment between the CTS absorber and ZnS buffer. Under the optimum parameters, power conversion efficiency (PCE) of CTS-based solar cells was boosted from 16.53% to 17.05% when ZnS was used as a buffer layer instead of CdS.

Broadband absorption enhancement in carbon-based perovskite solar cell with a composite light trapping structure

Abstract: In this work, a composite light-trapping strategy based on [email protected]2 nanoparticles embedded inside the active layer and an antireflection coating on the top surface is proposed to obtain broadband absorption improvement in carbon-based perovskite solar cells (C–PSCs). The effects of geometrical parameters, including the radius and period of Ag nanoparticles, the thickness of the protective SiO2 shell and the thickness of the antireflection coating, on the light absorption are investigated using the finite-difference time-domain (FDTD) method. Simulation results illustrate that nearly full absorption of light can be achieved with the optimized structure parameters for a 600 nm thick perovskite layer using the composite light-trapping scheme. The short-circuit current density (JSC) exhibits an improvement of 24.8% relatively compared to the C-PSC without light management. The proposed composite light-trapping structure allows improved light utilization and saved material consumption in C–PSCs.

Undoped Drain Graded Doping (UDGD) based TFET design: An innovative concept

Abstract: The work deals with the implementation of charge plasma concept towards the formation of graded doping profile in the Drain region of Tunnel FET (TFET) device architecture. This new and innovative concept of graded doping profile in the lateral direction holds its merit towards stopping the ambipolar conduction in TFETs without affecting its off and the on state performance. The proposed device i.e. Undoped Drain Graded Doping based TFET (UDGD TFET) architecture is highly effective in suppressing the gate to drain and therefore the total gate capacitance values and thus also seems promising towards reduction in the dynamic power dissipation in TFETs. The architecture has also shown significant improvements for RF application in terms of cut-off frequency, Gain Bandwidth and Transit Time with optimized parameters such as gate work function, drain workfunction, channel length and drain region length when compared to conventional Tunnel FETs. • The proposed device i.e. UDGD TFET uses the charge plasma concept in a different way and helps in suppressing the device ambipolar behavior (reduced by 12 orders for φ MG ​= ​4.3eV) without affecting its DC on-state (tunneling at source/channel junction) and off-state Characteristics. • The idea to laterally dope the drain region with graded doping has proven its potential in rectifying the issue of tunneling across drain/channel junction. • The UDGD TFET has been primarily proposed with the motive to completely suppress the TFET ambipolarity has later on turned efficient in suppressing the device parasitic effects in terms of total gate capacitance (C gg ) and gate to drain capacitance (C gd ) parameter by approximately 88% and 48% respectively in comparison to Conventional TFET (C-TFET) Device. • Such meritorious advantages of UDGD TFET have uplifted the RF performance of C-TFETs in terms of significant improvements in device cut-off frequency (f T ), its Gain Bandwidth (GBW) value and Transit Time, τ when studied. • The performance of UDGD TFETs has also been optimized by tuning the φ MG, φ MD, L Ch and L D values where φ MG ​= ​4.3eV, φ MD ​= ​4.3eV, L Ch ​= ​32 ​nm and L D ​= ​20 ​nm has been reported as the optimized parameters.

Analysis and evaluation of Si(1-x) Ge(x) pocket on sensitivity of a dual-material double-gate dopingless tunnel FET label-free biosensor

Abstract: This work reports a sensitivity analysis for a dual-material double-gate dopingless Tunnel FET (DM-DG-DLTFET) biosensor carrying a Si (1-x) Ge (x) pocket for improved performance of an overall device. The biomolecules are immobilized in a cavity suitable for small-sized biomolecules detection and the performance of the device is investigated by calculating the electrical properties altered due to the dielectric modulation caused by presence and absence of biomolecules by commercially available ATLAS TM tool. The Si (1-x) Ge (x) pocket placed under the cavity at source-channel interface helps to attain better on-current which is usually less in case of other reported structures of Tunnel FETs. The variation in the composition of Ge is observed to obtain enhanced sensitivity. The device is studied for threshold voltage sensitivity of neutral as well as charged biomolecules and the nature of the present biomolecule is also determined using the transconductance-to-current ratio (g m /I ds ) which can also be considered as a sensing metric. The optimized device design has been proposed keeping track of the electrical and physical trade-offs. Our results show a maximum of 539.5 mV shift in the threshold voltage when dielectric constant (K) of the neutral biomolecule is varied from 1 to 12 which makes our device evidently an efficient candidate for label-free biosensing application. • A dual-material double-gate dopingless Tunnel FET biosensor with Si (1-x) Ge (x) pocket is presented for enhanced performance. • Sensitivity improvement in neutral as well as charged biomolecules is noticed. • Analysis of pocket with a variation of Ge content shows improvement in drain and threshold voltage sensitivity of the device. • The device shows a remarkable difference between using a doped pocket underneath the cavity and using no pocket at all.