Silvaco ATLAS Software Research Articles

Improvement the Breakdown Voltage and the On-resistance in the LDMOSFET: Double Buried Metal Layers Structure

In this paper, a new method is investigated to improve the breakdown voltage in the lateral power MOSFET transistors. The structure is based on Double Buried Metal Layers in the Lateral Diffused MOSFET and it is called DBML-LDMOSFET. The metal layers in the buried oxide under the drift region cause the electric field to be more uniform than the conventional structure. In the DBML-LDMOSFET Structure, the breakdown voltage is improved 25% compared to conventional structure and also the specific on-resistance is almost 11.32 mΩ.cm2. In order to investigate the performance of the structures, SILVACO-ATLAS software has been used and the results have been extracted.

Using energy band engineering to improve heterojunction solar cells efficiency

In recent years, extensive research has been done on silicon and germanium materials for solar cell structure. In this paper, the arrangement of layers is proposed as Si/SiGe/Ge/SiGe/Si for solar cell structure. The mole fraction of Germanium in Silicon-Germanium layers is graded. That is the cause of graded energy band. Because of that, the Structure entitled Band-gap Graded Solar cell (BG Solar Cell). In order to investigate the performance of this structure, SILVACO-ATLAS software has been used and the results have been extracted. The efficiency and short-circuit current density of BG solar cell are 11.9 % and 41.43 mA/cm2, respectively.

Simulation and optimization of InGaN Schottky solar cells to enhance the interface quality

Abstract The InGaN/GaN Schottky solar cell was numerically investigated under AM1.5 illuminations using Silvaco-Atlas software to reach high efficiencies. According to the simulation results, when the indium composition (xIn) exceeds 54%, the conversion efficiency drops sharply and a large valence band offset appears. This failure can be explained by the recombination of the generated carriers before their collection due to the large lattice mismatch in high indium compositions. To overcome this inability, an effective process is established to ameliorate the interface between n-InGaN and n-GaN and to enhance the Schottky solar cell performances. The obtained results predict a clear enhancement of the efficiency from 2.25% to 18.48% at xIn = 60%. An optimization of this structure achieves an important efficiency of 21.69% for the optimal value of xIn = 54%, metal work function Wf = 6.3 eV, doping concentration Nd = 2 × 1017 cm−3 and an InGaN layer thickness TInGaN = 0.18 μm.

Analytical Modeling of ZrO2, HfO2 and SiO2 Effect over Tunneling Field Effect Transistor

These days, tunneling field effect transistors (TFET) for their ability in decrease of off-current transistors and also for electronic device power consumption, it is best point out for a scientist to research on this kind of transistors. By reducing off-current, on-current decreases too in compare to MOSFET transistors. Researchers are trying to reduce-off-current so that a minimum decrease in on-current occurs. One of the methods is to select a suitable oxide for the gate electrode. This paper presents an analytical model for the potential distribution of ZrO2, HfO2 and SiO2 effect over TFET. Using the potential distribution, the tunneling drain current is derived analytically by integrating the band-to-band tunneling generation rate over the device volume. The all-clear proposed that analytical models are validated via numerical results obtained from device simulations in SILVACO ATLAS software based on a non-local band-to-band tunneling model. Then results were ompared together. The results show the optimized on-current against off-current ratio and subthreshold swing.

Experimental and simulation studies on FTO/ZnO:Co/CuO hetero-junction structure for solar cell application

The performance of FTO/ZnO:Co/CuO hetero-junction structure is investigated using the Slivaco-Atlas software. The single oxide films were prepared by spray pyrolysis method on glass substrates in order to characterize the proper material parameters. Structural and morphological analysis confirmed the deposition of FTO, ZnO:Co, and CuO films with porous structures. The extracted physical properties such as thickness, optical and electrical parameters are considered as input data for Silvaco-Atlas software simulation. It was found that thickness layers and carrier concentration of CuO based solar cell play an important role in determining solar cell performances. The combination of the optimum parameters enables to obtain the efficiency of 24.55% which is improved with 8.88% compared to the calculated one using the proper experimental parameters.

Effects of high-k gate dielectrics on the electrical performance and reliability of an amorphous indium-tin-zinc-oxide thin film transistor (a-ITZO TFT): an analytical survey.

This study is a numerical simulation obtained by using Silvaco Atlas software to investigate the effect of different types of dielectric layers, inserted between the channel and the gate, on the performance and reliability of an a-ITZO TFT. Replacing the SiO2 oxide layer with a high-k dielectric layer gives the concept of the electrical thickness, known by the equivalent oxide thickness (EOT) in which the physical thickness (PT) can be increased to improve the device reliability without increasing the effective thickness of the gate dielectric. A range of different high-k dielectric materials was suggested. For low-k SiO2 (k = 3.9), the electrical parameters extracted are: Ci = 3.45 × 10-8 F cm-2, Ion = 2.23 × 10-6 A, Ioff = 2.17 × 10-13 A, Ion/Ioff = 1.02 × 107, EOT = 100 nm, VT = -0.61 V, μFE = 29.75 cm2 V-1 s-1, SS = 7.91 × 10-2 V per decade and Von = -0.95 V. Replacing SiO2 by a high-k dielectric material, such as SrTiO3 (k = 300), leads to effects similar to the effects of reducing the physical thickness of the gate dielectric but without actually reducing this physical thickness. This allows improving the outputs of the a-ITZO TFT as it leads to an increase in Ci, Ion and Ion/Ioff to the values Ci = 2.66 × 10-6 F cm-2, Ion = 2.86 × 10-4 A, and Ion/Ioff = 8.80 × 109, respectively, and the decrease in EOT, Ioff, VT, μFE, SS and Von to the values EOT = 1.3 nm, Ioff = 3.25 × 10-14 A, VT = -0.428 V, μFE = 26.66 cm2 V-1 s-1, SS = 6.12 × 10-2 V per decade and Von = -0.75 V, respectively, without leakage effects.

Effect of mole fraction, doping concentration and gate length on the electrical characteristics of nanoelectronic High Electron Mobility Transistor

Abstract In this work, we have optimized the device structure to achieve a maximum drain current of Nanoelectronic AlGaN/GaN single-heterojunction high electron mobility transistors (HEMTs) by the variations of mole fraction, doping concentration and gate length, using the SILVACO-ATLAS software tool. The drain current increases at higher aluminium mole fraction of AlGaN nano-layer. The drain current increases at higher doping concentration of AlGaN nano-layer. The drain current reduces at higher gate length of HEMTs. The conduction band engineering in terms of quantum wells is investigated in detail by involving the Bose-Einstein expression. The simulation results of this work are supported by the available previous experimental results and analytical modelling. This work will be useful to fabricate the AlGaN/GaN HEMTs experimentally for bioengineering applications.

Numerical investigation of strain effects on properties of AlGaAs/InGaAs multiple quantum well solar cells.

The effects of strain on the electronics and optical properties of a p-i-n solar cell, composed of AlGaAs/InGaAs semiconductor multiple quantum wells, are investigated. The lattice mismatch between AlGaAs and InGaAs induces strain on the composite material; thus the solar cell structure is simulated first with strain and then without strain. Finally, the short-circuit current, fill factor, and cell efficiency for the two approaches are compared in order to determine the effects of the mentioned mismatch on the solar cell properties. In addition, the results are indicated for quantum wells, with different numbers and width. Moreover, the mole fraction of aluminum content of the material varies from 0.1 to 0.3. The simulations are carried out with the Silvaco-Atlas software package ver. 3.20.2.R. Our results show that the existence of strain leads to improvement of the solar cell operation.

Numerical simulation of highly efficient dye sensitized solar cell by replacing the liquid electrolyte with a semiconductor solid layer

A dye-sensitized solar cell (DSSC) with FTO/TiO2/Dye/Electrolyte/FTO structure was simulated by using SILVACO ATLAS software. To optimize the charge transfer at the TiO2/dye/electrolyte interface, an Al-Modified TiO2 layer was used and its influence on photovoltaic performance was investigated. Optimized solar cell showed maximum power conversion efficiency of 7.67% with short-circuit current of 16.50 mA/cm2 and open-circuit voltage of 0.72 V at 100 mW cm−2 (1.5 A M).To resolve the difficulties regarding the use of liquid electrolyte, a solid-state dye-sensitized solar cell (SS-DSSC) was simulated in which a P3HT layer acts as a hole collector instead of liquid electrolyte. SS-DSSC indicated a favorable performance deliver a short-circuit photocurrent of 12.70 mA cm−2 and open-circuit voltage of 0.67 V.

CIGS Solar Cells for Space Applications: Numerical Simulation of the Effect of Traps Created by High-Energy Electron and Proton Irradiation on the Performance of Solar Cells

Numerical simulation is carried out using the Silvaco ATLAS software to predict the effect of 1-MeV electron and 4-MeV proton irradiation on the performance of a Cu(In, Ga)Se2 (CIGS) solar cell that operates under the air mass zero spectrum (AM0). As a consequence of irradiation, two types of traps are induced including the donor- and acceptor-type traps. Only one of them (the donor-type trap) is found responsible for the degradation of the open-circuit voltage (VOC), fill factor (FF) and efficiency (η), while the short circuit current (JSC) remains essentially unaffected. The modelling simulation validity is verified by comparison with the experimental data. This article shows that CIGS solar cells are suited for space applications.

Design and Simulation of InGaN/GaN p–i–n Photodiodes

InGaN ternary alloys with their band gaps varying from 0.7 to 3.4 eV, are very promising for photodetector devices operating from UV to IR wavelength range. Using Silvaco–Atlas software, an In0.1Ga0.9N/GaN based p–i–n photodiode is designed and the J–V characteristics, the spectral responsivity, the frequency response and the cut‐off frequency as a function of InGaN thickness are studied. The photodiode exhibits a high reverse breakdown voltage of 38 V, a peak responsivity of 0.2 A W−1 at 0.343 μm wavelength and a cutoff frequency of 400 MHz under an applied reverse bias voltage of 2 V and for a 0.1 μm i‐InGaN layer, in good agreement with simulated and experimental results found in literature. It is found that an optimum i‐layer thickness of 1.5 μm for the maximum cutoff frequency of 4 GHz attributed to the predominance of the limitation in capacitance effect on the cutoff frequency at low i‐layer thickness and the transit time on the cuttoff frequency for high i‐layer thickness. For this i‐layer thickness, the highest peak responsivity about 0.244 A W−1 at 0.384 μm wavelength is achieved.

Temperature Dependence of the Energy Band Diagram of AlGaN/GaN Heterostructure

Temperature dependence of the energy band diagram of AlGaN/GaN heterostructure was investigated by theoretical calculation and experiment. Through solving Schrodinger and Poisson equations self-consistently by using the Silvaco Atlas software, the energy band diagram with varying temperature was calculated. The results indicate that the conduction band offset of AlGaN/GaN heterostructure decreases with increasing temperature in the range of 7 K to 200 K, which means that the depth of quantum well at AlGaN/GaN interface becomes shallower and the confinement of that on two-dimensional electron gas reduces. The theoretical calculation results are verified by the investigation of temperature dependent photoluminescence of AlGaN/GaN heterostructure. This work provides important theoretical and experimental basis for the performance degradation of AlGaN/GaN HEMT with increasing temperature.

Influence on Characteristics of RTD Due to Variation of Different Parameters and Material Properties

In this paper, novel features offered by Resonant Tunneling Diode (RTD) are reviewed by simulating it under different conditions. GaAs/AlGaAs based RTD is used as the reference one to obtain the characteristics due to parametric variations. To fulfil this purpose a simple model of resonant electronic transport through a double-barrier structure is developed. I-V characteristics are studied by varying barrier parameters and well width. Different peak and valley currents are measured under these conditions. For the same set of parameters both symmetric and asymmetric cases are considered. Different materials of lower effective mass are also taken into consideration to improve Peak to Valley Ratio (PVR). The Indium (In) based materials are considered to compare the characteristics obtained from the conventional GaAs based RTD structure. All these proposed structures are simulated using Silvaco Atlas software.

11.73% efficient perovskite heterojunction solar cell simulated by SILVACO ATLAS software

A Perovskite sensitized solar cell was simulated using SILVACO ATLAS software and the obtained results were compared with the experimental data. The newly modeled Perovskite sensitized solar cell with ITO/TiO2/Perovskite/PEDOT/Au structure by focusing on photo-generation, carrier dissociation and photo-current creation processes provided promising results with the conversion efficiency of 11.73% and the Fill Factor (FF) of 70.10% under the AM1.5 illumination.

Current density of anodes, recombination rate and luminance in MEH-PPV, MDMO-PPV, and P3HT polymers in polymer light-emitting diodes

The present study examined polymer-based organic light-emitting diodes (PLEDs) with the different active layers using Silvaco Atlas software. The electrical and optical responses of the devices were evaluated through the characteristics of current-voltage, luminance, and recombination rate. The performance of the device strongly depends on the physical properties of the active layer. A better understanding of the effect of varying the parameters of the active layer, such as mobility, lifetime, and band gap, on the functioning of the device is necessary to achieve further improvement in these applications. This work presents a theoretical study of PLEDs having different active layers. Poly[2-methoxy-5-(3’,7’-dimethyloctyloxy)-1,4-phenylenevinylene], poly(3-hexylthiophene), and poly[2-methoxy-5-(2’-ethylhexyloxy)-p-phenylene vinylene] organic layers were deposited on an ITO substrate and the structure of the device was completed by a calcium cathode with a work function of 2.9 eV. The Langevin and Poole-Frenkel models were used to analyze the devices. The Langevin model was used to analyze the recombination rate and investigate the relationship between luminance, recombination rate, and the parameters of the active layer that have been less studied in previous works. Analysis of anode current density, luminance, and recombination rate indicate that poly(3-hexylthiophene) PLED shows better performance than others.

Structural and physical characteristics optimization of a dual junction CGS/CIGS solar cell: A numerical simulation

The structure and performance parameters of a dual junction CGS/CIGS solar cell including a CdS antireflection top layer are studied and optimized using Silvaco ATLAS software to obtain maximum possible value of efficiency. To gain a optimized design, the affects of CIGS bottom cell band gap and n-type doping concentration on the efficiency of the cell were examined and the optimum values of these parameters were obtained. In continue, the maximum JSC which is occurs when the current values of the two sub-cells are matched was obtained by varying the thickness of CdS layer, where an optimum efficiency of 43.05% is achieved.

Influence of doped Alq3 layer on performance of MEH-PPV, MDMO-PPV, and P3HT polymer light-emitting diodes

The present study examined the influence of a doped Tris(8-hydroxyquinolinato) aluminium (Alq3). Layer on the performance of polymer-based organic light-emitting diodes (PLEDs) using Silvaco Atlas software. The luminance and recombination rate of a device depends on the physical properties of the active layer and of the effective layers on the active layer. Insertion of a doped Alq3 layer between the active layer and cathode increased the recombination rate of the middle layer that had been limited by the anode and cathode of the device. Better understanding the effect of the doped Alq3 layer on the parameters of mobility, lifetime, and band gap of the active layer and the performance of the device is necessary to achieve further improvement in these applications. This work presents a theoretical study of the influence of the Alq3 layer on PLEDs having different active layers. Poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV), poly(3-hexylthiophene) (P3HT), and poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) organic layers were deposited onto an ITO substrate that was completed using calcium as a cathode with a work function of 2.9 eV. The Langiven model was used to analyze the recombination rate and luminance and indicated that the doped Alq3 layer between the active layer and cathode increased performance of the middle layer and improved the P3HT, MEH-PPV, and MDMO-PPV PLEDs. The MEH-PPV device showed the most improvement in comparison with the MDMO-PPV and P3HT devices. This originated from appropriate overlapping of the doped Alq3 layer and the MEH-PPV active layer.

Numerical simulation of CdS quantum dot sensitized solar cell using the Silvaco-Atlas software

In this study the Silvaco TCAD software was used for modeling and simulation of two photovoltaic devices with ITO/TiO2/P3HT&PCBM/Ag and ITO/TiO2/CdS/P3HT&PCBM/Ag structures. All the simulation results were compared to experimental measurement data of fabricated solar cells (Chen and Li, 2013) [1]. The current density–voltage (J–V) characteristics and the external quantum efficiency (EQE) were simulated under AM1.5G illumination. The simulated photovoltaic parameters of solar cells, short-circuit current density of 5.80mA/cm2, open circuit voltage of 0.61V, the fill factor of 50% and the conversion efficiency 1.8% was obtained for the CdS QDSSC which are in good agreement with the experimental high record data. This improved efficiency is attributed to the increase in light absorption by inserting the CdS QD layer.

An optimized efficient dual junction InGaN/CIGS solar cell: A numerical simulation

The photovoltaic performance of an efficient double junction InGaN/CIGS solar cell including a CdS antireflector top cover layer is studied using Silvaco ATLAS software. In this study, to gain a desired structure, the different design parameters, including the CIGS various band gaps, the doping concentration and the thickness of CdS layer are optimized. The simulation indicates that under current matching condition, an optimum efficiency of 40.42% is achieved.

Two-Dimensional Modelling and Simulation of CIGS Thin-Film Solar Cell

2 D Silvaco Atlas software is used for the study of a CIGS thin film solar cell in the configuration : ZnO(200 nm)/n-type CdS(50 nm)/ p-type CIGS(350 nm)/Mo. The cell performance is evaluated by implementing the defects created at the grain boundaries of the polycrystalline CdS and CIGS material and at the interface CdS/CIGS.The J-V characteristics and the external quantum efficiency EQE are simulated under AM 1.5 illumination. The conversion efficiency  of 20.35% is reached and the other (...)