Search Results (51)

Intermediate-band photovoltaics promise single-junction efficiencies that exceed the Shockley and Queisser limit, yet viable material platforms and device geometries remain under debate. Here, we perform comprehensive two-dimensional device-scale simulations using Silvaco Atlas TCAD to analyze p-i-n In_0.20Ga_0.80N solar cells in which the intermediate band is supplied by In_0.35Ga_0.65N quantum dots located inside the intrinsic layer. Quantum-dot diameters from 1 nm to 10 nm and areal densities up to 116 dots per period are evaluated under AM 1.5G, one-sun illumination at 300 K. The baseline pn junction achieves a simulated power-conversion efficiency of 33.9%. The incorporation of a single 1 nm quantum-dot layer dramatically increases efficiency to 48.1%, driven by a 35% enhancement in short-circuit current density while maintaining open-circuit voltage stability. Further increases in dot density continue to boost current but with diminishing benefit; the highest efficiency recorded, 49.4% at 116 dots, is only 1.4 percentage points above the 40-dot configuration. The improvements originate from two-step sub-band-gap absorption mediated by the quantum dots and from enhanced carrier collection in a widened depletion region. These results define a practical design window centred on approximately 1 nm dots and about 40 dots per period, balancing substantial efficiency gains with manageable structural complexity and providing concrete targets for epitaxial implementation. Full article

Aiming at the problems of low withstand voltage and poor RF performance of traditional HEMT devices, a new AlGaN/GaN high electron mobility transistor device with a π-gate (NπGS HEMT) is designed in this paper. The new structure incorporates a π-gate design along with a PN-junction field plate and an AlGaN back-barrier layer. The device is modeled and simulated in Silvaco TCAD 2015 software and compared with traditional t-gate HEMT devices. The results show that the NπGS HEMT has a significant improvement in various characteristics. The new structure has a higher peak transconductance of 336 mS·mm⁻¹, which is 13% higher than that of the traditional HEMT structure. In terms of output characteristics, the new structure has a higher saturation drain current of 0.188 A/mm. The new structure improves the RF performance of the device with a higher maximum cutoff frequency of about 839 GHz. The device also has a better performance in terms of voltage withstand, exhibiting a higher breakdown voltage of 1817 V. These results show that the proposed new structure could be useful for future research on high voltage withstand and high RF HEMT devices. Full article

Vertical GaN P-i-N diodes exhibit excellent high-voltage performance, fast switching speed, and low conduction losses, making them highly attractive for power applications. However, their breakdown voltage is severely constrained by electric field crowding at device edges. Using silvaco tcad (2019) tools, this work systematically evaluates multiple edge termination techniques, including deep-etched mesa, beveled mesa, and field-plate configurations with both vertical and inclined mesa structures. We present an optimized multi-drift-layer GaN P-i-N diode incorporating field-plate termination and analyze its electrical performance in detail. This study covers forward conduction characteristics including on-state voltage, on-resistance, and their temperature dependence, reverse breakdown behavior examining voltage capability and electric field distribution under different temperatures, and switching performance addressing both forward recovery phenomena, i.e., voltage overshoot and carrier injection dynamics, and reverse recovery characteristics including peak current and recovery time. The comprehensive analysis offers practical design guidelines for developing high-performance GaN power devices. Full article

We propose a novel ultraviolet (UV) phototransistor (PT) architecture based on an AlGaN/GaN high electron mobility transistor (HEMT) with a buried p-GaN layer. In the dark, the polarization-induced two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction interface is depleted by the buried p-GaN and the conduction channel is closed. Under UV illumination, the depletion region shrinks to just beneath the AlGaN/GaN interface and the 2DEG recovers. The retraction distance of the depletion region during device turn-on operation is comparable to the thickness of the AlGaN barrier layer, which is an order of magnitude smaller than that in the conventional p-GaN/AlGaN/GaN PT, whose retraction distance spans the entire GaN channel layer. Consequently, the proposed device demonstrates significantly enhanced weak-light detection capability and improved switching speed. Silvaco Atlas simulations reveal that under a weak UV intensity of 100 nW/cm², the proposed device achieves a photocurrent density of 1.68 × 10⁻³ mA/mm, responsivity of 8.41 × 10⁵ A/W, photo-to-dark-current ratio of 2.0 × 10⁸, UV-to-visible rejection ratio exceeding 10⁸, detectivity above 1 × 10¹⁹ cm·Hz^1/2/W, and response time of 0.41/0.41 ns. The electron concentration distributions, conduction band variations, and 2DEG recovery behaviors in both the conventional and novel structures under dark and weak UV illumination are investigated in depth via simulations. Full article

This study proposed a novel perovskite/silicon heterojunction (SHJ) tandem device structure without an interlayer, represented as ITO/NiO/perovskite/SnO₂/MoO_X/i-a-Si:H/n-c-Si/i-a-Si:H/n-a-Si:H/Ag, which was investigated by Silvaco TCAD software. The recombination layer in this structure comprises the carrier transport layers of SnO₂ and MoO_X, where MoO_X serves dual functions, acting as the emitter for the SHJ bottom cell and as part of the recombination layer in the tandem cell. First, the effects of different recombination layers are analyzed, and the SnO₂/MoO_X layer demonstrates the best performance. Then, we systematically investigated the impact of the carrier concentration, interface defect density, thicknesses of the SnO₂/MoO_X layer, different hole transport layers (HTLs) for the top cell, absorption layer thicknesses, and perovskite defect density on device performance. The optimal carrier concentration in the recombination layer should exceed 5 × 10¹⁹ cm⁻³, the interface defect density should be below 1 × 10¹⁶ cm⁻², and the thicknesses of SnO₂/MoO_X should be kept at 20 nm/20 nm. CuSCN has been found to be the optimal HTL for the top cell. When the silicon absorption layer is 200 μm, the perovskite layer thickness is 470 nm, and the defect density of the perovskite layer is 10¹¹ cm⁻³, the planar structure can achieve the best performance of 32.56%. Finally, we studied the effect of surface texturing on the SHJ bottom cell, achieving a power conversion efficiency of 35.31% for the tandem cell. Our simulation results suggest that the simplified perovskite/SHJ tandem solar cell with a dual-functional MoO_X layer has the potential to provide a viable pathway for developing high-efficiency tandem devices. Full article

Modern multi-junction solar cell technology offers a pathway to achieving consistent and high photovoltaic conversion efficiencies through enhanced solar spectrum absorption. Indeed, during the last years, the industries of solar cells have focused on optimizing device structures, utilizing both robust and delicate materials to maximize their performances. This paper presents the modeling and optimization of the electrical and structural properties of high-efficiency InGaP/GaAs double-junction solar cells, specifically without employing an anti-reflective coating. This developed structure has been achieved by introducing a buffer layer in the lower layer and incorporating an upper back surface field layer into the investigated cell structure. Furthermore, the optimization conducted in this paper using Silvaco-Atlas software (version 2018) under the AM1.5G spectrum reveals that the proposed InGaP/GaAs tandem cell configuration exhibits significant performance, reaching conversion efficiency of 41.585%. It can be said that this adapted structure yields a short-circuit current density of 21.65 mA/cm², an open-circuit voltage of 2.319 V, and a filling factor of 84.001%. Whereas this newly optimized structure demonstrates its effectiveness in enhancing solar cell efficiency performance, presenting highly promising results with potential significance for the devices’ optical and electrical properties. Full article

In this work, floating-gate organic field-effect transistor memory using the n-type semiconductor poly-{[N,N′-bis(2-octyldodecyl) naphthalene-1,4,5,8-bis (dicarbo- ximide)-2,6-dili]-alt-5,5′-(2,2′-bithiophene)} (N2200) as a charge-trapping layer is presented. With the assistance of a technology computer-aided design (TCAD) tool (Silvaco-Atlas), the storage characteristics of the device are numerically simulated by using the carrier injection and Fower–Nordheim (FN) tunneling models. The shift in the transfer characteristic curves and the charge-trapping mechanism after programming/erasing (P/E) operations under different P/E voltages and different pulse operation times are discussed. The impacts of different thicknesses of the tunneling layer on storage characteristics are also analyzed. The results show that the memory window with a tunneling layer thickness of 8 nm is 16.1 V under the P/E voltage of ±45 V, 5 s. After 1000 cycle tests, the memory shows good fatigue resistance, and the read current on/off ratio reaches 10³. Full article

With the growing demand for more efficient power conversion and silicon reaching its theoretical limit, wide bandgap semiconductor devices are emerging as a potential solution. For instance, Gallium Nitride (GaN)-based high-electron-mobility transistors (HEMTs) are getting more attention, and several structures for the normally off operation have been proposed. Adding an AlN interlayer in conventional AlGaN/GaN normally on HEMT structures is known to enhance the current density. In this work, the effect of an AlN interlayer in the normally off AlGaN/GaN MISHEMT with a buried p-region was investigated using a TCAD simulation from Silvaco. The added AlN interlayer increases the two-dimensional electron gas density, requiring a higher p-doping concentration to achieve the same threshold voltage. The simulation results show that the overall effect is a reduction in the device’s current density and peak transconductance by 21.83% and 44.4%, respectively. Further analysis of the current profile shows that because of the buried p-region and at high gate voltages, the current flows near the AlGaN/GaN interface and along the insulator/AlGaN interface. Adding an AlN interface blocks the migration of channel electrons to the insulator/AlGaN interface, resulting in a lower current density. Full article

This study systematically investigates the effects of anode metals (Ti/Au and Ni/Au) with different work functions on the electrical and temperature characteristics of β-Ga₂O₃-based Schottky barrier diodes (SBDs), junction barrier Schottky diodes (JBSDs) and P-N diodes (PNDs), utilizing Silvaco TCAD simulation software, device fabrication and comparative analysis. From the perspective of transport characteristics, it is observed that the SBD exhibits a lower turn-on voltage and a higher current density. Notably, the V_on of the Ti/Au anode SBD is merely 0.2 V, which is the lowest recorded value in the existing literature. The V_on and current trend of two types of PNDs are nearly consistent, confirming that the contact between Ti/Au or Ni/Au and NiO_x is ohmic. A theoretical derivation reveals the basic principles of the different contact resistances and current variations. With the combination of SBD and PND, the V_on, current density, and variation rate of the JBSD lie between those of the SBD and PND. In terms of temperature characteristics, all diodes can work well at 200 °C, with both current density and V_on showing a decreasing trend as the temperature increases. Among them, the PND with a Ni/Au anode exhibits the best thermal stability, with reductions in V_on and current density of 8.20% and 25.31%, respectively, while the SBD with a Ti/Au anode shows the poorest performance, with reductions of 98.56% and 30.73%. Finally, the reverse breakdown (BV) characteristics of all six devices are tested. The average BV values for the PND with Ti/Au and Ni/Au anodes reach 1575 V and 1550 V, respectively. Moreover, although the V_on of the JBSD decreases to 0.24 V, its average BV is approximately 220 V. This work could provide valuable insights for the future application of β-Ga₂O₃-based diodes in high-power and low-power consumption systems. Full article

This study proposes an AlGaN/GaN current aperture vertical electron transistor (CAVET) featuring a double superjunction (SJ) to enhance breakdown voltage (BV) and investigates its electrical characteristics via technology computer-aided design (TCAD) Silvaco Atlas simulation. An additional p-pillar was formed beneath the gate current blocking layer to create a lateral depletion region that provided a high off-state breakdown voltage. To address the tradeoff between the drain current and off-state breakdown voltage, the key design parameters were carefully optimized. The proposed device exhibited a higher off-state breakdown voltage (2933 V) than the device with a single SJ (2786 V), although the specific on-resistance of the proposed method (1.29 mΩ·cm⁻²) was slightly higher than that of the single SJ device (1.17 mΩ·cm⁻²). In addition, the reverse transfer capacitance was improved by 15.6% in the proposed device. Full article

As semiconductor devices become smaller, their performance and integration density improve, but new negative effects emerge due to the reduced distance between structures. In DRAM, these effects can lead to data loss or require additional refresh cycles, causing performance degradation. Specifically, in the 6F² DRAM structure, activating a word line (WL) lowers the energy barrier of adjacent WLs, leading to the Pass Gate Effect (PGE). This study investigates the use of buried oxide beneath the WL to mitigate the PGE through simulation. Using SILVACO TCAD, we analyzed the impact of varying the size and position of the buried oxide on the PGE. The results showed that increasing the oxide size or reducing the distance to the WL effectively reduced the PGE. However, the presence of interface traps, which increase with the addition of buried oxide, was found to exacerbate the PGE, indicating that minimizing interface traps is crucial when incorporating buried oxide. Full article

Historically, multi-junction solar cells have evolved to capture a broader spectrum of sunlight, significantly enhancing efficiency beyond conventional solar technologies. In this study, we utilized Silvaco TCAD tools to optimize a five-junction solar cell composed of AlInP, AlGaInP, AlGaInAs, GaInP, GaAs, InGaAs, and Ge, drawing on advancements documented in the literature. Our research focused on optimizing these cells through sophisticated statistical modeling and material innovation, particularly examining the relationship between layer thickness and electrical yield under one sun illumination. Employing III-V tandem solar cells, renowned for their superior efficiency in converting sunlight to electricity, we applied advanced statistical models to a reference solar cell configured with predefined layer thicknesses. Our analysis revealed significant positive correlations between layer thickness and electrical performance, with correlation coefficients (R² values) impressively ranging from 0.86 to 0.96 across different regions. This detailed statistical insight led to an improvement in overall cell efficiency to 44.2. A key innovation in our approach was replacing the traditional germanium (Ge) substrate with Copper Indium Gallium Selenide (CIGS), known for its adjustable bandgap and superior absorption of long-wavelength photons. This strategic modification not only broadened the absorption spectrum but also elevated the overall cell efficiency to 47%. Additionally, the optimization process involved simulations using predictive profilers and Silvaco Atlas tools, which systematically assessed various configurations for their spectral absorption and current–voltage characteristics, further enhancing the cell’s performance. These findings underscore the critical role of precise material engineering and sophisticated statistical analyses in advancing solar cell technology, setting new efficiency benchmarks, and driving further developments in the field. Full article

This paper investigates the behavior of SiC MOSFETs body diode reverse recovery as a function of different operating conditions. The knowledge of their effects is crucial to properly designing and driving power converters based on SiC devices, in order to optimize the MOSFETs commutations aiming at improving efficiency. Indeed, reverse recovery is a part of the switching transient, but it has a significant role due to its impact on recovery energy and charge. The set of different operating conditions has been properly chosen to prevent or force the snappy recovery of the device under testing. The experimental results and specific software simulations have revealed phenomena unknown in the literature. More specifically, the analysis of the reverse recovery charge, Q_rr, revealed two unexpected phenomena at high temperatures: it decreased with increasing gate voltage; the higher the device threshold, the higher the Q_rr. TCAD-Silvaco (ATLAS v. 5.29.0.C) simulations have shown that this is due to a displacement current flowing in the drift region due to the output capacitance voltage variation during commutation. From the analysis of the snappy recovery, it has emerged that there is a minimum forward current slope, below which the reverse recovery cannot be snappy, even for a high current level. Once this current slope is reached, Q_rr varies with the forward current only. Full article

This study proposed a novel double-layer junction termination structure for vertical diamond-based PN junction diodes (PND). The effects of the geometry and doping concentration of the junction termination structure on the PNDs’ electrical properties are investigated using Silvaco TCAD software (Version 5.0.10.R). It demonstrates that the electric performances of PND with a single n-type diamond layer are sensitive to the doping concentration and electrode location of the n-type diamond. To further suppress the electric field crowding and obtain a better balance between breakdown voltage and on-resistance, a double-layer junction termination structure is introduced and evaluated, yielding significantly improved electronic performances. Those results provide some useful thoughts for the design of vertical diamond PND devices. Full article

In this study, the electrical performance and bias stability of InSnO/a-InGaZnO (ITO/a-IGZO) heterojunction thin-film transistors (TFTs) are investigated. Compared to a-IGZO TFTs, the mobility (µ_FE) and bias stability of ITO/a-IGZO heterojunction TFTs are enhanced. The band alignment of the ITO/a-IGZO heterojunction is analyzed by using X-ray photoelectron spectroscopy (XPS). A conduction band offset (∆E_C) of 0.5 eV is observed in the ITO/a-IGZO heterojunction, resulting in electron accumulation in the formed potential well. Meanwhile, the ∆E_C of the ITO/a-IGZO heterojunction can be modulated by nitrogen doping ITO (ITON), which can affect the carrier confinement and transport properties at the ITO/a-IGZO heterojunction interface. Moreover, the carrier concentration distribution at the ITO/a-IGZO heterointerface is extracted by means of TCAD silvaco 2018 simulation, which is beneficial for enhancing the electrical performance of ITO/a-IGZO heterojunction TFTs. Full article