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To seek an earth-abundant and environmentally friendly absorber for thin-film solar cells, Cu3PSe4 is investigated by first-principles calculations and device simulations. We demonstrate that the compound has a suitable band gap width of 1.3 eV as well as a high sunlight absorption coefficient. However, drawbacks like small electron affinity, high hole concentration, large lattice mismatch with CdS, etc., are revealed, which may degrade the photovoltaic performance. To address those shortcomings, we propose (1) to optimize the carrier concentration by preparing the samples at low temperature and under a Cu-rich environment, (2) to replace the CdS buffer layer by a more suitable wide-gap semiconductor with smaller lattice mismatch, and (3) that the selected buffer layer should have small electron affinity in order to reduce the open-circuit voltage losses. After implementation of these optimization approaches, the device simulations demonstrate that the power conversion efficiency reaches 17.7% for a solar cell with the configuration Mo/Cu3PSe4/WS2/n-ZnO. The combination of first-principles calculations at the atomistic level and device simulations at the macroscopic level provides an appropriate approach to design ideal solar cells.

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Recently GeSe has developed as a promising light harvesting material by enjoying to its optical and electrical features as well as earth-abundant and low-toxic constituent elements. Nevertheless, the power conversion efficiency of GeSe-based solar cells yet lags far behind the Shockley-Queisser limit. In this work, we systematically designed, simulated and analyzed the highly efficient GeSe thin-film solar cells by SCAPS-1D. The influence of thickness and defect density of light harvest material, GeSe/CdS interface defect density, electron transport layer (ETL), electrode work function and hole transport layer (HTL) on the device output are carefully analyzed. By optimizing the parameters (thickness, defect, concentration, work function, ETL and HTL), an impressive PCE of 17.98% is delivered along with Jsc of 37.11 mA/cm2, FF of 75.53%, Voc of 0.61 V. This work offers theoretical guidance for the design of highly efficient GeSe thin film solar cells.

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In this paper, the single event effect of 6T-SRAM is simulated at circuit level and device level based on a 22 nm fully depleted silicon-on-insulator (FDSOI) process, and the effects of charge sharing and bipolar amplification are considered in device-level simulation. The results demonstrate that, under the combined influence of these two effects, the circuit's upset threshold and critical charge decreased by 15.4% and 23.5%, respectively. This indicates that the charge sharing effect exacerbates the single event effects. By analyzing the incident conditions of two different incident radius particles, it is concluded that the particles with a smaller incident radius have a worse impact on the SRAM circuit, and are more likely to cause the single event upset in the circuit, indicating that the ionization distribution generated by the incident particle affects the charge collection.

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Interfacial modification is a promising strategy to fabricate highly efficient perovskite solar cells (PSCs). Nevertheless, research studies about optimization for the performance of Dion-Jacobson (DJ)-phase quasi-2D PSCs by underlying surface modification are rarely reported. The relevant influence of interfacial modification on defect regulation in the bulk and at the interface for PSCs is still unexplored. Herein, an interlayer of polyaspartic acid (PASP) was introduced at the interface of a hole transporting layer and a perovskite absorber to regulate both the film quality and interface property for BDA-based DJ quasi-2D PSCs (n = 5). The PASP interlayer suppressed the charge recombination, restricted the interfacial charge accumulation, and promoted the charge transport in devices and therefore improved the power conversion efficiency of PSCs from 15.03 to 17.34%. Moreover, through device simulation, it was concluded that the increase of open-circuit voltage (Voc) was mainly attributed to the suppression of interface defects, while the increase of short-circuit current (Jsc) was ascribed to the restriction of interface defects and perovskite bulk defects. The improvement of both Voc and Jsc originated from the passivation of shallow defect states. The present work provides a promising route for the fabrication of efficient quasi-2D PSCs and enriches the fundamental understanding of defect regulation on photovoltaic performance.

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As people develop higher standards for the beauty of urban architecture, more and more architectural designs are exploring sources of natural lighting, such as glass curtain walls and glass domes. However, the pursuit of architectural design aesthetics introduces glare into buildings, which can be uncomfortable and even dangerous for health. Scholars in related fields have carried out many theoretical studies and design activities based on this problem. In this study, we focus on issues of glare in public buildings, aiming to improve light comfort by solving this problem. First, we propose an improved design strategy based on IDEO design thinking by adding the step of diverging from the design scheme. Second, guided by the results of a questionnaire survey and light environment simulations, we avoided the subjective simplicity of the traditional design process. Third, taking the main library of Shanghai Jiao Tong University as an example, we designed a movable sunshade that could effectively reduce glare effects and improve visual comfort, which improved the light comfort in public buildings. The simulation results show that the proposed design can be useful in buildings to effectively control glare and improve visual comfort and health.

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With the aim of decreasing the number of experiments to obtain a perovskite solar cell (PSC) with maximum theoretical efficiency, in this paper, PSC performance was studied using the program solar cell capacitance simulator (SCAPS-1D). The PSC with the architecture ITO/TiO2/perovskite/spiro-MeOTAD/Au was investigated, while the selected perovskite was mixed cation Rb0.05Cs0.1FA0.85PbI3. The analysis was based on an experimentally prepared solar cell with a power conversion efficiency of ~7%. The PSC performance, verified by short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE), was studied by optimization of the simulation parameters responsible for improvement of the cell operation. The optimized parameters were absorber layer thickness, doping, defect concentration and the influence of the resistivity (the net effect of ohmic loss, Rs and the leakage current loss represented by the resistivity, Rshunt). The results of SCAPS-1D simulations estimated the theoretical power conversion efficiency of 15% for our material. We have showed that the main contribution to improvement of solar cell efficiency comes with lowering ohmic resistivity of the cell as well as doping and defect concentration, because their concentration is proportional to recombination rate.

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The dependency of device degradation on bending direction and channel length is analyzed in terms of bandgap states in amorphous indium-gallium-zinc-oxide (a-IGZO) films. The strain distribution in an a-IGZO film under perpendicular and parallel bending of a device with various channel lengths is investigated by conducting a three-dimensional mechanical simulation. Based on the obtained strain distribution, new device simulation structures are suggested in which the active layer is defined as consisting of multiple regions. The different arrangements of a highly strained region and density of states is proportional to the strain account for the measurement tendency. The analysis performed using the proposed structures reveals the causes underlying the effects of different bending directions and channel lengths, which cannot be explained using the existing simulation methods in which the active layer is defined as a single region.

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Monte Carlo (MC) simulations play an important role in radiotherapy, especially as a method to evaluate physical properties that are either impossible or difficult to measure. For example, MC simulations (MCSs) are used to aid in the design of radiotherapy devices or to understand their properties. The aim of this article is to review the MC method for device simulations in radiation therapy. After a brief history of the MC method and popular codes in medical physics, we review applications of the MC method to model treatment heads for neutral and charged particle radiation therapy as well as specific in-room devices for imaging and therapy purposes. We conclude by discussing the impact that MCSs had in this field and the role of MC in future device design.

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Due to their remarkable properties, single-layer 2-D materials appear as excellent candidates to extend Moore's scaling law beyond the currently manufactured silicon FinFETs. However, the known 2-D semiconducting components, essentially transition metal dichalcogenides, are still far from delivering the expected performance. Based on a recent theoretical study that predicts the existence of more than 1800 exfoliable 2-D materials, we investigate here the 100 most promising contenders for logic applications. Their current versus voltage characteristics are simulated from first-principles, combining density functional theory and advanced quantum transport calculations. Both n- and p-type configurations are considered, with gate lengths ranging from 15 down to 5 nm. From this large collection of electronic materials, we identify 13 compounds with electron and hole currents potentially much higher than those in future Si FinFETs. The resulting database widely expands the design space of 2-D transistors and provides original guidelines to the materials and device engineering community.

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Electrical and carrier transport properties in In-Ga-Zn-O thin-film transistors (IGZO TFTs) with a heterojunction channel were investigated. For the heterojunction IGZO channel, a high-In composition IGZO layer (IGZO-high-In) was deposited on a typical compositions IGZO layer (IGZO-111). From the optical properties and photoelectron yield spectroscopy measurements, the heterojunction channel was expected to have the type-II energy band diagram which possesses a conduction band offset (ΔEc) of ~0.4 eV. A depth profile of background charge density indicated that a steep ΔEc is formed even in the amorphous IGZO heterojunction interface deposited by sputtering. A field effect mobility (µFE) of bottom gate structured IGZO TFTs with the heterojunction channel (hetero-IGZO TFTs) improved to ~20 cm2 V-1 s-1, although a channel/gate insulator interface was formed by an IGZO-111 (µFE = ~12 cm2 V-1 s-1). Device simulation analysis revealed that the improvement of µFE in the hetero-IGZO TFTs was originated by a quantum confinement effect for electrons at the heterojunction interface owing to a formation of steep ΔEc. Thus, we believe that heterojunction IGZO channel is an effective method to improve electrical properties of the TFTs.

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Engineering the energetics of perovskite photovoltaic devices through deliberate introduction of dipoles to control the built-in potential of the devices offers an opportunity to enhance their performance without the need to modify the active layer itself. In this work, we demonstrate how the incorporation of molecular dipoles into the bathocuproine (BCP) hole-blocking layer of inverted perovskite solar cells improves the device open-circuit voltage (VOC) and, consequently, their performance. We explore a series of four thiaazulenic derivatives that exhibit increasing dipole moments and demonstrate that these molecules can be introduced into the solution-processed BCP layer to effectively increase the built-in potential within the device without altering any of the other device layers. As a result, the VOC of the devices is enhanced by up to 130 mV, with larger dipoles resulting in higher VOC. To investigate the limitations of this approach, we employ numerical device simulations that demonstrate that the highest dipole derivatives used in this work eliminate all limitations on the VOC stemming from the built-in potential of the device.

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In this study, we investigate direct current (DC)/alternating current (AC) characteristic variability induced by work function fluctuation (WKF) with respect to different nanosized metal grains and the variation of aspect ratios (ARs) of channel cross-sections on a 10 nm gate gate-all-around (GAA) nanowire (NW) metal-oxide-semiconductor field-effect transistor (MOSFET) device. The associated timing and power fluctuations of the GAA NW complementary metal-oxide-semiconductor (CMOS) circuits are further estimated and analyzed simultaneously. The experimentally validated device and circuit simulation running on a parallel computing system are intensively performed while considering the effects of WKF and various ARs to access the device's nominal and fluctuated characteristics. To provide the best accuracy of simulation, we herein calibrate the simulation results and experimental data by adjusting the fitting parameters of the mobility model. Transfer characteristics, dynamic timing, and power consumption of the tested circuit are calculated using a mixed device-circuit simulation technique. The timing fluctuation mainly follows the trend of the variation of threshold voltage. The fluctuation terms of power consumption comprising static, short-circuit, and dynamic powers are governed by the trend that the larger the grain size, the larger the fluctuation.

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Current advanced transistor architectures, such as FinFETs and (stacked) nanowires and nanosheets, employ truly three-dimensional architectures. Already for aggressively scaled bulk transistors, both statistical and systematic process variations have critically influenced device and circuit performance. Three-dimensional device architectures make the control and optimization of the device geometries even more important, both in view of the nominal electrical performance to be achieved and its variations. In turn, it is essential to accurately simulate the device geometry and its impact on the device properties, including the effect caused by non-idealized processes which are subject to various kinds of systematic variations induced by process equipment. In this paper, the hierarchical simulation system developed in the SUPERAID7 project to study the impact of variations from equipment to circuit level is presented. The software system consists of a combination of existing commercial and newly developed tools. As the paper focuses on technological challenges, especially issues resulting from the structuring processes needed to generate the three-dimensional device architectures are discussed. The feasibility of a full simulation of the impact of relevant systematic and stochastic variations on advanced devices and circuits is demonstrated.

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Localized impurities doped in the semiconductor substrate of nanostructure devices play anessential role in understanding and resolving transport and variability issues in device characteristics.Modeling discrete impurities under the framework of device simulations is, therefore, an urgent needfor reliable prediction of device performance via device simulations. In the present paper, we discussthe details of the physics associated with localized impurities in nanostructure devices, which areinherent, yet nontrivial, to any device simulation schemes: The physical interpretation and the roleof electrostatic Coulomb potential in device simulations are clarified. We then show that a naiveintroduction of localized impurities into the Poisson equation leads to a logical inconsistency withinthe framework of the drift-diffusion simulations. We describe a systematic methodology for how totreat the Coulomb potential consistently with both the Poisson and current-continuity (transport)equations. The methodology is extended to the case of nanostructure devices so that the effects of theinterface between different materials are taken into account.

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Herein we propose a new equivalent circuit including double heterojunctions in series to simulate the current-voltage characteristic of P-I-N planar structure perovskite solar cells. This new method can theoretically solve the dilemma of the parameter diode ideal factor being larger than 2 from an ideal single heterojunction equivalent circuit, which usually is in the range from 1 to 2. The diode ideal factor reflects PN junction quality, which influences the recombination at electron transport layer/perovskite and perovskite/hole transport layer interface. Based on the double PN junction equivalent circuit, we can also simulate the dark current-voltage curve for analyzing recombination current (Shockley-Read-Hall recombination) and diffusion current (including direct recombination), and thus carrier recombination and transportation characteristics. This new model offers an efficacious and simple method to investigate interfaces condition, film quality of perovskite absorbing layer and performance of transport layer, helping us further improve the device efficiency and analyze the working mechanism.

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Core-shell nanowires offer great potential to enhance the efficiency of light-emitting diodes (LEDs) and expand the attainable wavelength range of LEDs over the whole visible spectrum. Additionally, nanowire (NW) LEDs can offer both improved light extraction and emission enhancement if the diameter of the wires is not larger than half the emission wavelength (λ/2). However, AlGaInP nanowire LEDs have so far failed to match the high efficiencies of traditional planar technologies, and the parameters limiting the efficiency remain unidentified. In this work, we show by experimental and theoretical studies that the small nanowire dimensions required for efficient light extraction and emission enhancement facilitate significant loss currents, which result in a low efficiency in radial NW LEDs in particular. To this end, we fabricate AlGaInP core-shell nanowire LEDs where the nanowire diameter is roughly equal to λ/2, and we find that both a large loss current and a large contact resistance are present in the samples. To investigate the significant loss current observed in the experiments in more detail, we carry out device simulations accounting for the full 3D nanowire geometry. According to the simulations, the low efficiency of radial AlGaInP nanowire LEDs can be explained by a substantial hole leakage to the outer barrier layer due to the small layer thicknesses and the close proximity of the shell contact. Using further simulations, we propose modifications to the epitaxial structure to eliminate such leakage currents and to increase the efficiency to near unity without sacrificing the λ/2 upper limit of the nanowire diameter. To gain a better insight of the device physics, we introduce an optical output measurement technique to estimate an ideality factor that is only dependent on the quasi-Fermi level separation in the LED. The results show ideality factors in the range of 1-2 around the maximum LED efficiency even in the presence of a very large voltage loss, indicating that the technique is especially attractive for measuring nanowire LEDs at an early stage of development before electrical contacts have been optimized. The presented results and characterization techniques form a basis of how to simultaneously optimize the electrical and optical efficiency of core-shell nanowire LEDs, paving the way to nanowire light emitters that make true use of larger-than-unity Purcell factors and the consequently enhanced spontaneous emission.

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The Boltzmann transport equation is commonly considered to be the best semi-classical description of carrier transport in semiconductors, providing precise information about the distribution of carriers with respect to time (one dimension), location (three dimensions), and momentum (three dimensions). However, numerical solutions for the seven-dimensional carrier distribution functions are very demanding. The most common solution approach is the stochastic Monte Carlo method, because the gigabytes of memory requirements of deterministic direct solution approaches has not been available until recently. As a remedy, the higher accuracy provided by solutions of the Boltzmann transport equation is often exchanged for lower computational expense by using simpler models based on macroscopic quantities such as carrier density and mean carrier velocity. Recent developments for the deterministic spherical harmonics expansion method have reduced the computational cost for solving the Boltzmann transport equation, enabling the computation of carrier distribution functions even for spatially three-dimensional device simulations within minutes to hours. We summarize recent progress for the spherical harmonics expansion method and show that small currents, reasonable execution times, and rare events such as low-frequency noise, which are all hard or even impossible to simulate with the established Monte Carlo method, can be handled in a straight-forward manner. The applicability of the method for important practical applications is demonstrated for noise simulation, small-signal analysis, hot-carrier degradation, and avalanche breakdown.

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Through advanced electro-thermal simulations we demonstrate that self-heating effects play a significant role in ultrascaled nanowire field-effect transistors, that some crystal orientations are less favorable than others (⟨111⟩ for n-type applications, ⟨100⟩ for p-type ones), and that Ge might outperform Si at this scale. We further establish a relationship between the dissipated power and the electrical mobility and another one between the current reduction induced by self-heating and the phonon thermal conductivity.

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In this work, we study the impact of random interface traps (RITs) at the interface of SiO x /Si on the electrical characteristic of 16-nm-gate high-κ/metal gate (HKMG) bulk fin-type field effect transistor (FinFET) devices. Under the same threshold voltage, the effects of RIT position and number on the degradation of electrical characteristics are clarified with respect to different levels of RIT density of state (D it). The variability of the off-state current (I off) and drain-induced barrier lowering (DIBL) will be severely affected by RITs with high D it varying from 5 × 10(12) to 5 × 10(13) eV(-1) cm(-2) owing to significant threshold voltage (V th) fluctuation. The results of this study indicate that if the level of D it is lower than 1 × 10(12) eV(-1) cm(-2), the normalized variability of the on-state current, I off, V th, DIBL, and subthreshold swing is within 5%.