Superlattices and Microstructures最新文献

Zinc sulfide (ZnS) is an emerging alternate n-type buffer layer for the cadmium-free thin-film solar cells. The present research adopts a unique mixture of glycerol and tartaric acid for the emergence of phase-pure ZnS during pulse electrodeposition. Besides, proper optimization of pulse parameters aid in producing crystalline ZnS films with no post-deposition heat treatment. The as-deposited films exhibit cubic ZnS as confirmed from X-Ray Diffraction (XRD) and micro-Raman analyses. The optical study reveals an average transmittance of 71% in the wavelength spread of 300–900 nm with a band gap of 3.8 eV. The n-type semiconducting behavior of ZnS is affirmed from the Mott-Schottky analysis and the flat band potential is inferred to be −1.0 V vs SCE. The crystalline ZnS films produced from the economic pulse electrodeposition method devoid of heat treatment step, with their demonstration as photoanode in photoelectrochemical cells are suitable for the relevant applications.

We present a novel and comprehensive quantum analytical modeling of a sub-20 nm Dual Metal Double Gate (DMDG) Tunnel Field Effect Transistor (TFET) for the first time in literature. Owing to structural confinement at sub-20 nm regime, the energy states at channel are quantized and carrier propagation is regulated by quantum transport. We address such quantization aspects (viz. subband quantization, bandgap shifting, tunneling through barrier etc.) and incorporate them in analytical modeling using self-consistent solution of Schrödinger-Poisson's equation. As a result of work function difference at gate, we observe creation of quantum well, followed by a tunneling barrier, along the channel. Energy states in the quantum well are derived from Schrodinger equation, whereas, transmission coefficients are derived for each tunneling barrier. Finally, current density is obtained using ‘Landauer formula for quantum transport’. We methodically study the effects of structural confinement on device performances and observe significant shift from classical counterpart. Moreover, we note that quantization in DMDG TFET can be optimized that will lead to superior device performance. The results are verified with simulation data in each occasion to substantiate analytical models.

As the energy problem becomes more prominent, research on thermoelectric (TE) materials has deepened over the past few decades. Low thermal conductivity enables thermoelectric materials better thermal conversion performance. In this study, based on the first principles and phonon Boltzmann transport equation, we studied the thermal conductivities of single-layer WSe₂ under several defect conditions using density functional theory (DFT) as implemented in the Vienna Ab-initio Simulation Package (VASP). The lattice thermal conductivities of WSe₂ under six kinds of defect states, i.e., PS, SS-c, DS-s, SW-c, SS-e, and DS-d, are 66.1, 41.2, 39.4, 8.8, 42.1, and 38.4 W/(m·K), respectively at 300 K. Defect structures can reduce thermal conductivity up to 86.7% (SW-c) compared with perfect structure. The influences of defect content, type, location factors on thermal properties have been discussed in this research. By introducing atom defects, we can reduce and regulate the thermal property of WSe₂, which should provide an interesting idea for other thermoelectric materials to gain a lower thermal conductivity.

This work investigated the thermoelectric properties of Cu₂ZnSnS₄ (CZTS) thin films deposited on the soda-lime glass using spin-coating techniques with different layers. X-ray diffraction (XRD) pattern confirms the increase of the layer number leads to improve the crystallite size and all the films exhibit tetragonal structure with the presence of secondary phases. EDX shows a reduction of Cu and Zn contents while an increase in Sn contents is observed when the thickness increases. Surface topography is also carried out to study the surface roughness and it is found to be minimum when we deposit 4 layers. The absorption spectra show that CZTS exhibit a bandgap varied between 1.33 and 1.9 eV, the resistivity and the Seebeck coefficient have been found to increase with the increase of surface roughness. This investigation indicates that Cu₂ZnSnS₄ thin films can be a suitable material for thermoelectric application at near room temperature range.

The high-voltage interconnection (HVI) effect induces electric field crowding at the drift region near the source side of power lateral double diffusion MOS (LDMOS). Thus, the electric field profile is deteriorated, and the breakdown characteristic is weakened. This increases the difficulty of device optimization and affects the reliability of the device significantly. Since conventional models based 2-D method can only treat the HVI as a metal layer, therefore, no quantitative analysis can be provided. In order to quantify the impact of the HVI and provide a design scheme for preventing the deterioration in the device's breakdown characteristic, a novel three-dimensional analytical model of the HVI effect for the SOI LDMOS is proposed. By solving the 3-D Poisson's equation, the potential and electric field distribution of the drift region surface are investigated, and the breakdown mechanism is explored quantitatively. The analytical solutions are matched well with the simulation results, which verify the validity of the model. Based on the model, a simple and effective criterion is derived to optimize the structure geometry parameters. The largest width of the HVI metal line is given to prevent the breakdown voltage deterioration.

In this work, a recent heuristic method called Dragonfly Algorithm (DA) has been employed for the first time to investigate the temperature effect on the Schottky diode electrical parameters. Beryllium-doped Al_0.29Ga_0.71As Schottky diodes grown by molecular beam epitaxy (MBE) have been used to validate the suggested method. The proposed approach is based on the analysis of current-voltage-temperature (I–V-T) and capacitance-voltage (C–V) characteristics. Furthermore, the interface state density $\left(N_{ss}\right)$ as function of the difference between the surface state energy and valence band energy $(E_{ss}-E_V)$ was determined. The obtained results demonstrate the high efficiency of this strategy to accurately determine the electrical parameters and investigate their temperature dependency. This efficiency can be clearly remarked from the well fit between both predicted and measured current characteristics.

In this work, AlGaN/GaN HEMT pH sensitive response has been presented through extensive simulations demonstrating the effect of pH variation on channel conductance, potential and conduction band profile. The pH solution is defined by an intrinsic semiconductor material whose properties are modified to mimic electrolyte solution and the effect of variation in charged adsorbates is accommodated by adjusting the interface charges density at oxide-semiconductor interface. The effect of AlGaN barrier layer composition (thickness and Aluminum mole fraction) on the sensitivity was analyzed by simulating different device configurations using ATLAS Silvaco device simulation tool. The devices render improved voltage sensitivity (S_V = ΔV_r/pH) and high output current sensitivity (S_I = (ΔI_ds/pH) = 15 mA/mm-pH). The simulations predict a thinner barrier layer along with smaller mole fraction device is most sensitive to pH changes at the surface for an open gate operation.

Nanoplasmonics is a potential game-changer in the development of next-generation on-chip photonic devices and computers, owing to the geometrically controlled and amplified linear and nonlinear optical processes. For instance, it resolves the limited light-matter interaction of the unique two-dimensional (2D) crystalline materials like semiconducting monolayer molybdenum disulfide (1L-MoS₂). Metal grating (MG) substrates excel at this because their surface plasmons (SPs) can lead to stark field confinement near the surface. This work studies optical amplification of 1L-MoS₂ on the gold (Au) MG substrate, which was designed to operate in a glycerol environment with SP resonance (SPR) at 850 nm excitation wavelength. Its design was verified by simulated and experimental reflectances, and topographically inspected by atomic force microscopy (AFM). Two advanced imaging modalities, second harmonic generation (SHG) and confocal Raman microscopy (CRM) were used to evaluate its 170-fold SHG on- and 3-fold CRM off-resonance optical amplifications, respectively. Some MoS₂-to-grating adhesion issues due to trapped liquid showed as image nonuniformities. Possible improvements to limitations like surface roughness were also discussed. These Au MG substrates can boost conventional linear and nonlinear backscattering microscopies because they are tunable in the visible and near-infrared range by selecting geometry, metal, and environment.

In_yGa_1-yN templates are grown with y ≤ 13.5% and a few nm surface roughness. These templates are used successfully to address two of the main issues facing long wavelength emitting LEDs, mainly the low growth temperature and high values of strain in the quantum wells (QWs). In this work, three LED structures are investigated: the first is a blue LED grown on GaN, the second and third are green LEDs grown on relaxed In_yGa_1-yN templates with y of about 10% and 12%, respectively. The same multiple quantum wells (MQWs) were used in the three LED structures, with the same well width, barrier width, and growth temperature. The reduced strain in the QWs due to the use of InGaN templates enhances the indium incorporation rate in the QWs. Red shift in emission wavelength of about 100 nm, from 470 nm to 570 nm, was achieved, at low injection current. Optical output power and external quantum efficiency (EQE) measurements showed that at high level of current injection, performance of the blue LED is about twice of the green emitting LEDs on InGaN templates. The current results indicate the potential of the InGaN template approach, with high values of y, in addressing problems facing long wavelength InGaN LEDs.

Sensing COVID-19, GOx (glucose oxidase enzyme) in exhaled breath condensate/saliva, bio-molecules like KIM (Kidney Injury Molecule) in human body and pH value in human body fluids have gained huge attention in the present scenario as well as in the past decade. Hence, for the first time, double channel technique in AlGaN/GaN High Electron Mobility Transistor (HEMT) is proposed and its applicability is demonstrated by biosensing application. Simulation using SILVACO Technology Computer Aided Design (TCAD) based on numerical solid state models has been extensively used for investigation and analysis. The sensitivity of double channel device is compared with single channel device and its performance is evaluated in terms of the transconductance. Unlike the single channel device, double channel device exhibited wide range of transconductance with respect to gate bias. The device recorded a sensitivity of 136%, which is 74% higher than the sensitivity of single channel device. Hence, it is inferred that the sensitivity enhances with the use of multiple channels and could be increased by increasing the number of channels. The results of this research show that the proposed sensor stands a promising candidate for future biosensing applications that demand high detection limits.