Editorial

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Quality in Simulation-Only Manuscripts Submitted to J-EDS

In recent years the Journal of the Electron Device Society (J-EDS) has experienced an increasing number of submissions of "simulation only" manuscripts. One reason for this is the improved accuracy and maturity of physicsbased simulation tools, either Technology Computer Aided Design (TCAD) or circuit analysis programs, that allow researchers to explore, devise and optimize the best breakthroughs going beyond the state-of-the-art technology without the need for experimental validation

Characterization of the Dynamic RON of 600 V GaN Switches under Operating Conditions

High-voltage GaN switches can offer tremendous advantages over silicon counterparts for the development of high-efficiency switching-mode power converters at high commutation frequency. Nonetheless, GaN devices are prone to charge-trapping effects that can be particularly relevant in the early-stage development of new technologies. Charge-trapping mechanisms are responsible for the degradation of the dynamic ON-resistance (RON) with respect to its static value: this degradation is typically dependent on the blocking voltage, the commutation frequency and temperature, and is responsible for the reduction of power converter efficiency. The characterization of this phenomenon is very valuable for the development of a new process to compare different technological solutions or for the final assessment of performance. This characterization cannot be made with traditional static or small signal measurements since RON degradation is triggered by application-like dynamic device excitations. In this paper, we propose a technique for the characterization of the dynamic RON of high-voltage GaN switches under real operating conditions: this technique is based on the design of a half bridge switching leg in which the DUT is operated under conditions that resemble its operation in a power converter. With this setup, the characterization of a 600 V GaN switch dynamic RON is performed as a function of variable blocking voltages and commutation frequency. Additionally, this technique allows the separation of thermal and trapping effects, enabling the characterization of the dynamic RON at different temperature

Simulation Study of Light-induced, Current-induced Degradation and Recovery on PERC Solar Cells

Abstract The way to permanently recover the well-known Light-Induced Degradation (LID) which affects the p-type Cz-Si PERC solar cells represents one of the main challenges of photovoltaic research. In this work we have set up a numerical simulations flow which allows us to reproduce the experimental measured values of figures of merit (FOMs) of four different Cz-PERC solar cells lots subjected to a degradation and two regeneration processes. The recombination centres in bulk and the Boron-Oxygen complexes (B-O) are modeled by means of two trap levels tuned on the basis of experimental data. From simulations we confirm that the FOM degradation levels off after 16hours and the regeneration process characterized by relatively long time process is preferred in terms of performance recovery. In addition, further cells with different passivation films are analyzed by adopting the same methodology

Numerical Simulation of Vertical Silicon Nanowires based Heterojunction Solar Cells

Abstract Nanowires (NWs) solar cells are expected to outperform the thin-film counterparts in terms of optical absorptance. In this theoretical study we optimize the geometry of vertical crystalline-amorphous silicon core-shell NW arrays on doped ZnO:Al (AZO)-Glass substrate by means of 3-D optical simulations in order to maximize the photon absorption. The optimized geometry is investigated by means of 3-D TCAD numerical simulation in order to calculate the ultimate efficiency and the main figures of merit by taking into account recombination losses. We show that optimized 10 μm-long crystalline – amorphous silicon core-shell (c-Si/a-Si/AZO/Glass) NWs can reach photo-generated current up to 22.94 mA/cm 2 (above 45% larger than that of the planar counterpart with the same amount of absorbing material) and conversion efficiency of 13.95%

Simulation Study of Multi-wire front Contact Grids for Silicon Solar Cells

Abstract Multi-wire (MW) front-contact schemes represent a promising alternative to standard H-pattern structure with ribbon busbar (BB) in silicon solar cells. In the case of MW schemes, busbar are replaced by copper wires. MW have been demonstrated to enhance the photo-generation with respect to a standard H-pattern structure with ribbon busbar when solar cells are encapsulated and assembled in modules. However, the influence of the geometrical and optical properties of the encapsulation layers as well as of wires on the optical effective shading is not exhaustively treated by the literature. In this work, we have performed electro-optical simulations of MW and BB based solar cells in order to calculate the effective optical shading factor, the enhancement of conversion efficiency and the saving of contact-paste, with respect to the BB design. Specifically, we have studied by means of a ray-tracing simulation tool the significant impact of the front contact grid geometry, of the encapsulation layer thickness and of the optical properties of the cell front interface on the effective optical shading. The calculated values of effective optical shading are used to determine the enhancement of the figures of merit and the paste saving with respect to the reference silver BB scheme. On the basis of our calculations the adoption of optimized MW designs may enhance the conversion efficiency up to 0.5% abs , allowing paste saving up to 50 mg per cell

Hot-Carrier Degradation in Power LDMOS: Selective LOCOS-Versus STI-Based Architecture

In this paper, we present an analysis of the degradation induced by hot-carrier stress in new generation power lateral double-diffused MOS (LDMOS) transistors. Two architectures with the same nominal voltage and comparable performance featuring a selective LOCOS and a shallow-trench isolation are investigated by means of constant voltage stress measurements and TCAD simulations. In particular, the on-resistance degradation in linear regime is experimentally extracted and numerically reproduced under different stress conditions. A similar amount of degradation has been reached by the two architectures, although different physical mechanisms contribute to the creation of the interface states. By using a recently developed physics-based degradation model, it has been possible to distinguish the damage due to collisions of single high-energetic electrons (single-particle events) and the contribution of colder electrons impinging on the silicon/oxide interface (multiple-particle events). A clear dominance of the single-electron collisions has been found in the case of LOCOS structure, whereas the multiple-particle effect plays a clear role in STI-based device at larger gate-voltage stress

Numerical Simulation and Experimental Characterization of Emitter Wrap through Solar Cells with Deep Grooved Base Contact (EWT-DGB)

Abstract In this work we present an Emitter Wrap Through cell with Deep Grooved Base contact (EWT-DGB), designed for both 1-sun and concentrating applications. The proposed approach, which consists in a deep grooved hole array composed by holes of two alternating doping type, allows both a reduction of the cell series resistance and an increase in collection efficiency also by using relatively thick substrates with low lifetime. The measured experimental data including dark J-V characteristics, figures of merit (FOMs) under illumination and external quantum efficiency (EQE) are compared to the results of 3-D drift-diffusion TCAD numerical simulations. Moreover, the impact of the hole spacing and of process-dependent physical parameters (interface defects) on FOMs is investigated by means of simulations

A Comparative Study of MWT Architectures by Means of Numerical Simulations

AbstractIn order to improve the efficiency of c-Si and mc-Si solar cells, Metal Wrap Though (MWT) architecture is investigated. In this paper we implement TCAD numerical simulations to analyze the performance of MWT cells with a point busbar or a continuous busbar at the back side. The two topologies of MWT cells are compared in both illuminated and dark conditions, aiming at understanding and comparing the resistive and recombination losses. The impact of the separation region is also studied, highlighting the degradation effect on the Fill Factor (FF) and on the efficiency in the two structures. We observe that the separation region dimension leads to a higher degradation of efficiency in case of continuous busbar

Healthcare resource consumption and related costs of patients estimated with treatment-resistant depression in Italy

Purpose: To analyse the healthcare resource consumption and related costs for the Italian National Health System of patients estimated to be affected by treatment-resistant depression (TRD) in Italy. Patients and methods: This was an observational retrospective study based on administrative databases, including those related to residential/semiresidential structures, of Veneto Region and the Local Health Unit of Bergamo in Italy (for a total of around 6 million health-assisted subjects). Between July 2011 and December 2017, all adult patients with a third antidepressant (AD) after ≥2 AD (each one with at least ≥4 weeks duration, ≥1 prescription at maximum dosage reported in datasheets, a grace period ≤30 days when switching AD and treatment maintained ≥9 months) were included. Overall and psychiatry-related healthcare resources consumption and related costs were estimated on a 12-months based analysis. Data were re-proportioned to the Italian population. Results: We have previously estimated a total of 101,455 patients with TRD in Italy (130,049 considering the mean maximum dosage of AD). Of them, 44.2% had at least a psychiatric hospitalization/visit or accessed a residential/semiresidential structure, and 31% added another AD or a mood stabilizer/antipsychotic drug. Patients with at least one psychiatry-related hospitalization increased over the number of antidepressant lines from 12.0% during first line up to 24.5% during fourth line. Direct healthcare costs increased from €4,405 for first line to €9,251 from fifth line onwards. Psychiatry-related costs went from €1,817 (first line) to €4,606 (fifth line onwards) and were mainly driven by residential/semiresidential structures and hospitalizations. Conclusion: An upward trend with number of AD lines was observed for all healthcare resource utilization and consequently for all direct costs, thus indicating an increasing burden for patients as they move forward AD lines