Si Homojunction Research Articles

Performance assessment of an eco-friendly tandem solar cell based on double perovskite Cs2AgBiBr6

Tandem solar cells have a wider photon absorption range, allowing them to provide better efficiency than single-junction SC. The upper cell absorbs high-energy photons, while the lower cell absorbs low-energy filtered photons. However, in order to obtain affordable, efficient, and long-lasting SC, the absorber layers of the top and bottom cells must be integrated with an adequate bandgap. This research suggests tandem perovskite solar cells as upper band active materials in this setting. The Si homojunction solar cell's performance was improved by investigating the thicknesses of the p−type and n−type layers, doping concentrations, and defect densities. The thickness variation of the perovskite solar cell (100−400nm) is then optimized. To precisely replicate the tandem devices, the estimated spectra of the perovskite SC are optically filtered onto the lower cells. Current matching was achieved by adjusting the thickness of the perovskite sub-cell with different bottom layer thicknesses, and the optimized efficiency of 36.26% for the perovskite/Si tandem device was shown. The discoveries will open the door for the upcoming creation of high−efficiency, low-energy solar cells.

The Optimizing of Prefabricated Solar Cells by Dual Plasmonic Nanoparticles

Background: The quest for improving the efficiency of solar cells has garnered considerable attention in numerous scientific investigations. One promising approach involves utilizing plasmons generated by metal nanoparticles to enhance the performance of photovoltaic solar cells.
 Materials and Methods: High-purity gold nanoparticles (AuNPs), silver nanoparticles (AgNPs), and a combination of both were synthesized using pulsed laser ablation in distilled water. Subsequently, these nanoparticles were deposited onto silicon (Si) substrates and pre-existing Si homo-junction photovoltaic cells.
 Results: The optical analysis of the prepared nanoparticle suspension revealed distinct plasmonic bands located at approximately 400 nm and 523 nm wavelengths for AgNPs and AuNPs, respectively. In the case of the AuNPs:AgNPs mixture, two plasmonic bands were observed, corresponding to the presence of both types of metal nanoparticles. The X-ray diffraction (XRD) analysis of the deposited nanoparticle samples on Si wafers demonstrated a polycrystalline structure for all samples. Scanning electron microscopy (SEM) imaging displayed uniformly distributed spherical Au nanoparticles on the substrate, while AgNPs exhibited some aggregations.
 Conclusion: The photovoltaic (PV) solar cells demonstrated an enhanced performance, attributed to the ability of the plasmonic nanoparticles to facilitate increased light absorption or enhance surface conductivity. The combination of silver and gold particles holds promise for solar surface coating, further optimizing the cells to capture a greater amount of solar radiation within their plasmon peaks. This study highlights the potential of plasmonic nanoparticles to enhance the efficiency of previously prepared PV cells.

Paper-Thin Al-Catalyzed Si Nanowire Solar Cells and Efficiency Enhancement by Hybrid Nanostructures with Mn-Doped Perovskite Nanocrystals

The use of thin silicon (Si) wafers and streamlined fabrication methods that can be scaled up without compromising device efficiency is a key strategy for realizing low-cost and flexible solar cells. Herein, aluminum (Al)-catalyzed Si nanowires (NWs) formed by vapor–liquid–solid growth on paper-thin polished and etched Si(111) wafers of 100 and 60 μm thickness with high proficiency for minimizing interfacial defects and light absorption loss have been accomplished. Successfully addressing the major challenge of rapid Al catalyst oxidation by ex situ and uncomplicated growth conditions allows for the potential to scale up the process while preventing the formation of deep-level traps resulting from catalyst contamination. The Si NWs formed on the nanowave surface of a thin etched Si wafer evidence comparable light absorbance and low interfacial defects to those grown on thin polished and traditional Si wafers. Fabrication of thin Si NW solar cells with a homojunction p+–p–n–n+ structure toward the enhanced power conversion efficiency (PCE) by hybrid nanostructures with manganese-doped cesium lead chloride (CsPb0.81Mn0.19Cl3) perovskite nanocrystals (NCs) using a simple drop-casting method has been explicitly explained. The precise tuning of the energy band and NC size enabled a significant radiative energy transfer by matching the light absorption range of NCs with a high Stokes shift in the luminescence spectrum and the spectral response range of underlying Si solar cells. The nonradiative energy transfer efficiency of NCs and an NC amount infiltration on homojunction Si NW solar cells for maximizing PCE enhancement were examined. The effective photon-harvesting architectures of NWs and NCs together with efficient energy transfers and surface passivation from NCs to the underlying homojunction Si NW solar cells could capably enhance PCE up to a 9% level. These results exhibited the potential for feasible low-cost and large-scale fabrication techniques with lower consumption of raw materials for future photovoltaic applications.

Photovoltaic parameter extraction and optimisation of ZnO/GO based hybrid solar trigeneration system using SCAPS 1D

In this work, simulative investigation of Zinc Oxide/Graphene Oxide based novel hybrid solar trigeneration system has been performed to identify its photovoltaic parameters i.e. Current density (Jsc), Open circuit voltage (Voc), fill factor (FF), Power Conversion Efficiency (PCE), using SCAPS 1D (Solar Cell Capacitance Simulator) software. A comparison was made between the simulated and estimated experimental values for the cell under standard test conditions, which showed an all over good agreement. The simulated values of VOC, JSC, FF, PCE for ZnO/GO are 0.79 V, 12.46 mA/cm2, 52.14 %, 8.46 % respectively. The extracted experimental values are 0.72 V, 7.24 mA/cm2, 56.94 %, 9.12 % respectively. Further analysis is done to study the effect of graphene oxide layer thickness on PV properties of the cell. Also performance of ZnO/GO cell was compared to ZnO/SiO2 cell and it was found that the efficiency of the two is nearly similar when evaluated at 32 °C under 1 Sun and AM 1.5. A limiting factor in using the high-efficiency Si homojunction solar cell is its high fabrication cost. Hence here we try to replace GO with SiO2 because of its simpler synthesis and involved fabrication processes. But the only backdrop is its lower efficiency, which can be improved by rigorous simulation analysis of the organic semiconductor layer. The performance of the presented hybrid system has been estimated and differentiated with other known solar trigeneration system to evaluate the viability of the showcased model, provided physical constraints imposed by the environment are considered depending upon the system installation location.

Perovskite/Silicon Tandem Solar Cells with a Voc of 1784 mV Based on an Industrially Feasible 25 cm2 TOPCon Silicon Cell

Perovskite-based tandem solar cells are promising candidates for industrial applications. This study demonstrated perovskite/silicon tandem devices based on a conventional Si homojunction device configuration employing a tunnel oxide passivating contact to improve the voltage. Moreover, we fabricated it without the deposition of a recombination layer on a large area while showing the possibility of applying the industry market. This solar cell exhibited a power conversion efficiency of 17.3% and a high voltage of 1783 mV on a 25 cm2 active area.

A novel source material engineered double gate tunnel field effect transistor for radio frequency integrated circuit applications

Tunnel field effect transistors (TFETs) have proved their potential for many possible electronic circuit applications. However, with the variety of TFET structures being worked upon it has been an unresolved challenge to optimize them for the applications to which they are best suited. In this paper we present a detailed comparative analysis of the linearity distortion and the radiofrequency (RF) performance parameters of a proposed heterojunction Mg2Si source double gate TFET (HMSDG-TFET) and a conventional homojunction Si source DG-TFET (SSDG-TFET). A source material engineering scheme is utilized to implement a staggered type 2 heterojunction at the source–channel junction by replacing the source material with Mg2Si (a low band gap material) to enhance the ON current (2.5 × 10–4 A µm−1), reduce the threshold voltage (0.26 V) and achieve a steeper subthreshold swing (10.05 mV decade−1). For linearity and distortion analysis, the figure of merit (FOM)-like higher-order transconductances, second- and third-order voltage intercepts, third-order intercept point, third-order intermodulation distortion, zero crossover point, 1 dB compression point, second-order harmonic distortion, third order harmonic distortion and total harmonic distortion have been examined. To portray the possible application of devices under consideration for RF integrated circuit applications, both structures are investigated for RF FOMs such as power gains, cutoff frequency (fT), maximum oscillation frequency (F max) and admittance parameters. Investigations carried out using a Silvaco ATLAS device simulator tool revealed that with fT approximately three orders higher (0.49 THz) and F max approximately two orders higher (0.9 THz) than that of a SSDG-TFET, the HMSDG-TFET is an appropriate candidate for use in high-frequency, high-linearity, low-distortion and low-power analog/RF applications.

Interfacial Built-In Electric Field-Driven Direct Current Generator Based on Dynamic Silicon Homojunction.

Searching for light and miniaturized functional device structures for sustainable energy gathering from the environment is the focus of energy society with the development of the internet of things. The proposal of a dynamic heterojunction-based direct current generator builds up new platforms for developing in situ energy. However, the requirement of different semiconductors in dynamic heterojunction is too complex to wide applications, generating energy loss for crystal structure mismatch. Herein, dynamic homojunction generators are explored, with the same semiconductor and majority carrier type. Systematic experiments reveal that the majority of carrier directional separation originates from the breaking symmetry between carrier distribution, leading to the rebounding effect of carriers by the interfacial electric field. Strikingly, NN Si homojunction with different Fermi levels can also output the electricity with higher current density than PP/PN homojunction, attributing to higher carrier mobility. The current density is as high as 214.0 A/m2, and internal impedance is as low as 3.6 kΩ, matching well with the impedance of electron components. Furthermore, the N-i-N structure is explored, whose output voltage can be further improved to 1.3 V in the case of the N-Si/Al2O3/N-Si structure, attributing to the enhanced interfacial barrier. This approach provides a simple and feasible way of converting low-frequency disordered mechanical motion into electricity.

Optimization of device design for low cost and high efficiency planar monolithic perovskite/silicon tandem solar cells

Perovskite/silicon hybrid tandem solar cells are very close to commercialization owing to their low cost and relatively high efficiency compared to tandem cells based on III-V compound semiconductors. However, most hybrid tandem cell research is based on n-type heterojunction Si cells, which occupy only a small fraction of the total solar market. Here, we propose a new method for optimizing the design of low-cost and high-efficiency monolithic tandem cells based on p-type homojunction Si cells by realizing lossless current matching by simultaneously controlling the band gap energy and thickness of the perovskite film. In addition, systematic studies have been conducted to determine the optimal hole transport layer applicable to the tandem cell from the viewpoint of band alignment and process compatibility, in order to reduce the open-circuit voltage loss. Optimized tandem cells, which were fabricated with a 310 nm thick perovskite layer of (FAPbI3)0.8(MAPbBr3)0.2 and a hole transport layer of poly(triaryl amine), had a significantly increased efficiency of 21.19% compared to semi-transparent stand-alone perovskite (13.4%) and Si cells (12.8%). Our tandem cell represented the highest efficiency increment among all monolithic perovskite/Si tandem cells as well as the highest efficiency among monolithic perovskite/Si tandem cells based on p-type homojunction Si cells with Al back-surface fields. The design rules suggested in this study could also be applicable to different types of perovskite/Si tandem cells.

Modeling and optimization of core/shell p-i-n Si/Si0.2Ge0.8 nanowire for photovoltaic

In this work we propose a modeling and simulation of core/shell p-i-n Si/Si0.2Ge0.8 nanowire for photovoltaic. In the first step of this work, we have compared the core/shell p-i-n homojunction Si and heterojunction Si/Si0.2Ge0.8 Nanowire (NW) solar cell having a length of 3μm and a radius of 0.19μm, by studying their current-voltage and external quantum efficiency (EQE). Our results have shown that blending Silicon with 80% of Germanium enhances relatively the short circuit current and efficiency by 3.04% and 8.48% respectively. In other hand, the absorption edge of Silicon NW has extended from 1100nm to 1200nm, with a gain of EQE of 15% obtained in this range. In the second part, we have tried to optimize the Si/Si0.2Ge0.8 structure, by varying their radius and length. The corresponding results have indicated that a radius of 0.28μm and a length of 10μm are the optimal geometric parameters for any optimization of such structure.

Black phosphorus induced photo-doping for high-performance organic-silicon heterojunction photovoltaics

In conventional crystalline silicon (Si) homojunction solar cells, a strategy of doping by transporting phosphorus or boron impurities into Si is commonly used to build Ohmic contacts at rear electrodes. However, this technique involves an energy intensive, high temperature (∼800 °C) process and toxic doping materials. Black phosphorus (BP) is a two-dimensional, narrow bandgap semiconductor with high carrier mobility that exhibits broad light harvesting properties. Here, we place BP:zinc oxide (ZnO) composite films between Si and aluminum (Al) to improve their contact. Once the BP harvests photons with energies below 1.1 eV from the crystalline Si, the ZnO carrier concentration increases dramatically due to charge injection. This photo-induced doping results in a high carrier concentration in the ZnO film, mimicking the modulated doping technique used in semiconductor heterojunctions. We show that photo-induced carriers dramatically increase the conductivities of the BP-modified ZnO films, thus reducing the contact resistance between Si and Al. A photovoltaic power conversion efficiency of 15.2% is achieved in organic-Si heterojunction solar cells that use a ZnO:BP layer. These findings demonstrate an effective way of improving Si/metal contact via a simple, low temperature process.

Core-Shell P-N Junction Si Nanowires as Rapid Response and High-Sensitivity pH Sensor

High density, vertical well-aligned p-type, n-type, and core-shell p-n homojunction Si nanowires were synthesized on p-Si substrate. The morphology, crystalline structure, composition, and doping ratio of these Si nanowires were investigated via field emission scanning electron microscope, Raman spectra, and X-ray photoelectron spectroscopy. The pH sensors were fabricated with the typical extended-gate field-effect transistor method. The core-shell p-n junction Si nanowires samples had the best performance for pH sensitivity at 68 mV/pH compared with the p-Si NWs and n-Si NWs pH sensors. Furthermore, the pH sensing current of the core-shell p-n junction Si NWs sensor featured rapid response, good repeatability, and stability. The built-in potential $V_{bi}$ of the core-shell p-n homojunction Si nanowires is ~0.78 V, which improved the pH sensitivity.

Influence of Front and Back Contacts on Photovoltaic Performances of p-n Homojunction Si Solar Cell: Considering an Electron-Blocking Layer

In this simultion work, the effect of front and back contacts of p-n homojunction Si solar cell with an electron-blocking layer (EBL) has been studied with the help of a strong solar cell simulator named AMPS-1D (analysis of microelectronic and photonic structures one dimensional). Without the effect of these contact parameters, low solar cell efficiency has been observed. Fluorine-doped tin oxide (FTO) with high work function (5.45 eV) has been used as the front contact to the proposed solar cell. Zinc (Zn) metal which has a work function of 4.3 eV has been used as the back contact of the proposed model. With FTO as the front contact and Zn as the back contact, the optimum efficiency of 29.275% (Voc = 1.363 V, Jsc = 23.747 mA/cm2, FF = 0.905) has been observed. This type of simple Si-based p-n homojunction solar cell with EBL of high efficiency has been proposed in this paper.

A Computational Study of Tunneling Field-Effect Transistors: Challenges and Design Optimizations

Complementary-metal-oxide-semiconductor (CMOS) transistors have been commonly employed in the electronics industry for the past decades thank to their excellent scalability, low cost, and high performance. The semiconductor industry follows the Moore’s law which predicts that the number of transistors in an integrated circuit (IC) approximately doubles every two years. High packing density enables more logic circuits to be fabricated on a given IC chip area which lowers the cost per function. However, exponential growth of the number of transistors per IC chip leads to a drastic increase in the power density. Basically, power consumption of an IC can be categorized into two components: active power (PActive ) and passive power (PPassive ). PActive is given by αfCVDD 2 , where α is the activity factor, f is the operating frequency, C is the load capacitance, and VDD is the power supply voltage. PPassive is the power dissipation of transistors that are at the OFF state. Its magnitude is proportional to the product of OFF state current (IOFF ) and VDD . With the shrinking of physical dimensions of CMOS devices into sub-10 nanometer regime, direct source to drain tunneling and gate leakage can significantly increase the IOFF , which in turn increases the static power. In other words, power consumption has imposed a serious issue for advanced technology nodes. Since both active and passive powers are strongly dependent on the VDD , one effective way to reduce the power consumption is to scale down the VDD . The threshold voltage (VTH ) of the conventional MOSFETs needs to be reduced so that the same ION can be sustained at reduced VDD . However, decreasing VTH without scaling the subthreshold swing (S) will result in a high IOFF . This causes high passive power consumption. In the conventional MOSFET, the high energy electrons following the Fermi-Dirac distribution contribute to the subthreshold current which sets the lower limit of the subthreshold swing. Thus, a steeper switching characteristic is required in order to retain the same ION and IOFF when VDD is reduced. In this context, tunneling field-effect transistors (TFET) based on band-to-band tunneling (BTBT) is a promising candidate to overcome the 60mV/dec swing limitation at room temperature faced in conventional MOSFETs. Although a steeper switching characteristic can be achieved in TFETs, the ION of TFETs is still too low to satisfy the drive current requirement for low power application projected by the International Technology Roadmap for Semiconductors (ITRS). The performance of TFET can be enhanced via a few innovations, such as the employment of direct band gap materials, heterostructures with staggered band alignments, and inventive device structure designs. Recent advancements in TFET shows that enhancement in TFET is attained when the BTBT direction is aligned to the gate induced electric field, so-called vertical TFET (VTFET). This is due to the greater efficiency of the gate to control the band bending. In this work, we investigate the performance of the vertical TFET based on group IV and III-V materials. The vertical TFET considered is the Electron-Hole Bilayer TFET. The device Hamiltonians for all channel materials are constructed based on the full-band sp3d5s*tight-binding (TB) model. The atomistic TB model offers a realistic calculation which captures the properties of nano-scale structures more accurately. The carrier transport of VTFET is calculated using a quantum simulator based on the formalism of non-equilibrium Green’s function (NEGF). Subsequently, the atomic charge obtained from NEGF is coupled with the Poisson solver to solve for the atomic potential self-consistently. The optimization of VTEFT is carried out in terms of ON-current and subthreshold swing. The materials considered consist of silicon, germanium, and indium antimonide, and hetero-structures from III-V semiconductors. The effects of the device geometries, such as the length of overlap (LOV ) and underlap (LUN ) regions, are studied in order to provide insights in enhancing the electrical performance of VTFETs. Our study shows that heterojunction consisting of GaSb (source) and InAs (drain) offers higher current than that of Si homojunction. The electrical performance of VTEFT is further benchmarked with that of the conventional lateral PIN structure. In conclusion, this work presents the challenges and key design considerations of VTEFT.

Design of Si0.5Ge0.5 based tunnel field effect transistor and its performance evaluation

In this work, the performance comparison of two heterojunction PIN TFETs having Si channel and Si0.5Ge0.5 source with high-k (SiGe DGTFET HK) and hetero-gate dielectric (SiGe DGTFET HG) respectively with those of two homojunction Si based PIN (DGTFET HK and DGTFET HG) TFETs is performed. Similarly, by employing the technique of pocketing at source junction in above four PIN TFETs, the performances of resultant four PNPN TFETs (SiGe PNPN DGTFET HK, SiGe PNPN DGTFET HG, PNPN DGTFET HK and PNPN DGTFET HG) are also compared with each other. Due to lower tunnel resistance of SiGe based heterojunction PIN and PNPN TFETs, the DC parameters such as ON current, ON-OFF current ratio, average subthreshold slope are improved significantly as compared to Si based PIN and PNPN TFETs respectively. The output characteristics of HG architectures in Si based homojunction PIN and PNPN TFETs is observed to be identical to with respective Si based HK PIN and PNPN TFET architectures. However, the output characteristics of HG architectures in SiGe based heterojunction PIN and PNPN TFETs degrade as compared to their respective SiGe based HK PIN and PNPN TFET architectures. In ON state, SiGe based HK and HG PIN and PNPN TFETs have lower gate capacitance (Cgg) as compared to their respective Si based HK and HG PIN and PNPN TFETs. Moreover, HG architecture suppresses gate to drain capacitance (Cgd) and ambipolar conduction. Transconductance (gm) and cut off frequency (fT) is also observed to be higher for SiGe based PIN and PNPN TFETs.

Effect of Shell Growth and Doping Conditions of Core–Shell Homojunction Si Nanowire Solar Cells

Effects of shell growth and doping conditions on the structural, optical and photovoltaic properties of core-shell homojunction Si nanowire (SiNW) arrays have been investigated. Core-shell nanowires were fabricated using a combination of metal-catalyzed electroless etching (MCEE) and thermal chemical vapor deposition (CVD) techniques. SiNWs formed by MCEE technique readily bundles with each other, disturbing the formation of radial p-n junctions surrounding them. CVD has made it possible to form uniform p-type Si shell layers on n-type SiNWs formed by MCEE technique. Results of SEM and Raman measurements reveal that electrical active B concentration can be increased with increase of shell thickness by increasing doping gas fluxes and growth time while keeping good crystallinity. Reflectivity measurements show an increase of light reflection in the visible range with increasing shell thickness. The short circuit current (I(sc)) and fill factor (FF) closely depend on the shell growth time and the dopant gas flux for the growth of shell layers. These results show doping conditions to be a key parameter for core-shell homojunction SiNW solar cells.

Electronic and thermoelectric properties of nanograting layers

Recently, new quantum features have been observed and studied in the area of nanostructured layers. Nanograting (NG) on the surface of the thin layer imposes additional boundary conditions on electron wave function and forbids some quantum states. Electrons, rejected from the forbidden quantum states, have to occupy states with higher energy. In the case of semiconductor materials, electrons rejected from the valence band have to occupy empty quantum states in the conduction band. Such increase in conduction band electron concentration n can be termed as geometry-induced doping or G-doping. G-doping is equivalent to donor doping from the point of view of the increase in n. However, there are no ionized impurities. This preserves charge carrier scattering to the intrinsic semiconductor level and increases carrier mobility. G-doping involves electron confinement to NG layer. Here, we investigate the system of multiple NG layers forming a series of homo junctions. Si and GaAs homojunctions were studied and G-doping levels of 1018-1019 cm−3 were obtained. We also study a system composed of NG layer and an additional top layer forming periodic series of p-n junctions. In such system, charge depletion region develops inside the NG and its effective depth reduces, becoming a rather strong function of temperature T. Consequently, T-dependence of chemical potential magnifies and Seebeck coefficient S increases. We investigate S in the system of semiconductor NG layer having abrupt p-n junctions on the top of the grating. Analysis made on the basis of Boltzmann transport equations shows dramatic increase in S. At the same time, other transport coefficients remain unaffected by the junctions. Calculations show one order of magnitude increase in the thermoelectric figure of merit ZT relative to bulk material.

Geometry-induced electron doping in periodic semiconductor nanostructures

Recently, new quantum features have been observed and studied in the area of nanostructured layers. Nanograting on the surface of the thin layer imposes additional boundary conditions on the electron wave function and induces G-doping or geometry doping. G-doping is equivalent to donor doping from the point of view of the increase in electron concentration n. However, there are no ionized impurities. This preserves charge carrier scattering to the intrinsic semiconductor level and increases carrier mobility with respect to the donor-doped layer. G-doping involves electron confinement to the nanograting layer. Here, we investigate the system of multiple nanograting layers forming a series of hetero- or homojunctions. The system includes main and barrier layers. In the case of heterojunctions, both types of layers were G-doped. In the case of homojunctions, main layers were G-doped and barrier layers were donor-doped. In such systems, the dependence of n on layer geometry and material parameters was analysed. Si and GaAs homojunctions and GaAs/AlGaAs, Si/SiGe, GaInP/AlGAs, and InP/InAlAs heterojunctions were studied. G-doping levels of 1018–1019cm−3 were obtained in homojunctions and type II heterojunctions. High G-doping levels were attained only when the difference between band gap values was low.

Comparison of band-to-band tunneling models in Si and Si—Ge junctions

We compared several different band-to-band tunneling (BTBT) models with both Sentaurus and the two-dimensional full-band Monte Carlo simulator in Si homo-junctions and Si—Ge hetero-junctions. It was shown that in Si homo-junctions, different models could achieve similar results. However, in the Si—Ge hetero-junctions, there were significant differences among these models at high reverse biases (over 2 V). Compared to the nonlocal model, the local models in Sentaurus underrated the BTBT rate distinctly, and the Monte Carlo method was shown to give a better approximation. Additionally, it was found that in the Si region near the interface of the Si—Ge hetero-junctions, the direct tunneling rates increased largely due to the interaction of the band structures of Si and Ge.

Studies on Anisotype Si/Si1-xGex Heterojunction DDR IMPATTs: Efficient Millimeter-wave Sources at 94 GHz Window

In this paper, an attempt is made to investigate the millimeter-wave performance of anisotype Si/Si1-xGex heterojunction Double-drift region (DDR) Impact Avalanche Transit Time (IMPATT) devices operating at 94 GHz window frequency by using a generalized double-iterative computer method based on drift-diffusion model developed by the authors. Simulation study on both anisotype Np and nP type Si/Si1-xGex heterojunction DDR IMPATTs for Ge mole fractions, x = 0.1 and x = 0.3, is carried out and their mm-wave properties are compared with a Si homojunction DDR IMPATT operating at the same frequency. Results show that significant improvements in DC to RF conversion efficiency and RF power output can be achieved in Si/Si1-xGex heterojunction DDR IMPATTs as compared to their Si homojunction counterpart. It is observed that the mm-wave performance of nP Si0.7Ge0.3/Si heterojunction DDR as regards to RF power output and conversion efficiency is best among all the devices under consideration. DC to RF conversion efficiency and continuous wave (CW) RF power output of nP Si0 7Ge0 3/Si DDR are obtained as 20.04% and 731.7 mW, respectively, near 94 GHz; whereas for Si DDR, the same parameters are obtained as 10.40% and 609.3 mW, respectively.

Analysis of trap-assisted tunneling in vertical Si homo-junction and SiGe hetero-junction Tunnel-FETs

This paper reports on the integration of vertical nTunnel FETs (TFETs) with SiGe hetero-junction and analyzes the presence of trap-assisted tunneling impacting the device behavior. Temperature measurements are used to distinguish the band-to-band tunneling (BTBT) from the trap-assisted tunneling (TAT). It is shown that TAT degrades the onset characteristic and the subthreshold swing of the devices. TCAD simulations are in good agreement with experimental data for a germanium content up to 44%, when including non-local TAT model and properly tuning the model’s parameters. Simulations also suggest that boosting the BTBT component, for example by further bandgap decrease (Ge source), or by other means should be beneficial in lowering the impact of trap-assisted tunneling, provided that the material defectivity does not worsen.