Intrinsic Region Research Articles

Auger Suppression of Incandescence in Individual Suspended Carbon Nanotube pn-Junctions.

There are various mechanisms of light emission in carbon nanotubes (CNTs), which give rise to a wide range of spectral characteristics that provide important information. Here we report suppression of incandescence via Auger recombination in suspended carbon nanotube pn-junctions generated from dual-gate CNT field-effect transistor (FET) devices. By applying equal and opposite voltages to the gate electrodes (i.e., Vg1 = -Vg2), we create a pn-junction within the CNT. Under these gating conditions, we observe a sharp peak in the incandescence intensity around zero applied gate voltage, where the intrinsic region has the largest spatial extent. Here, the emission occurs under high electrical power densities of around 0.1 MW/cm2 (or 6 μW) and arises from thermal emission at elevated temperatures above 800 K (i.e., incandescence). It is somewhat surprising that this thermal emission intensity is so sensitive to the gating conditions, and we observe a 1000-fold suppression of light emission between Vg1 = 0 and 15 V, over a range in which the electrical power dissipated in the nanotube is roughly constant. This behavior is understood on the basis of Auger recombination, which suppresses light emission by the excitation of free carriers. Based on the calculated carrier density and band profiles, the length of the intrinsic region drops by a factor of 7-25× over the range from |Vg| = 0 to 15 V. We, therefore, conclude that the light emission intensity is significantly dependent on the free carrier density profile and the size of the intrinsic region in these CNT devices.

Radiation-induced electron and hole traps in Ge1 − xSnx (x = 0–0.094)

The band structure of germanium changes significantly when alloyed with a few percent concentrations of tin, and while much work has been done to characterize and exploit these changes, the corresponding deep-level defect characteristics are largely unknown. In this paper, we investigate the dominant deep-level defects created by 2 MeV proton irradiation in Ge1 − xSnx (x = 0.0, 0.020, 0.053, 0.069, and 0.094) diodes and determine how the ionization energies of these defects change with tin concentrations. Deep-level transient spectroscopy measurements approximate the ionization energies associated with electron transitions to/from the valence band (hole traps) and conduction band (electron traps) in the intrinsic regions of p-i-n diode test structures. The prominent deep-level hole traps may be associated with divacancies, vacancy–tin complexes, and vacancy–phosphorous complexes (V2, V–Sn, and V–P, respectively), with the presumed V–P hole trap dominating after room temperature annealing. The ionization energy level of this trap (approximated by the apparent activation energy for hole emission) is close to the intrinsic Fermi level in the 0% and 2% Sn devices and decreases as the tin concentration is increased, maintaining an approximately fixed energy spacing below the indirect conduction band edge. The other hole traps follow this same trend, and the dominant electron trap ionization energies remain roughly constant with changes in tin concentrations, indicating they are likewise pinned to the conduction band edge. These results suggest a pattern that may, in many cases, apply more generally to deep-level defects in these alloys, including those present in the “as-grown” materials.

Separating the two polarities of the POLO contacts of an 26.1%-efficient IBC solar cell

By applying an interdigitated back contacted solar cell concept with poly-Si on oxide passivating contacts an efficiency of 26.1% was achieved recently. In this paper the impact of the implemented initially intrinsic poly-Si region between p-type poly-Si and n-type poly-Si regions is investigated. Two recombination paths are identified: The recombination at the interface between the initially intrinsic poly-Si and the wafer as well as the recombination across the resulting p(i)n diode on the rear side which is aimed to be reduced by introducing an initially intrinsic region. By using test structures, it is demonstrated that the width of the initially intrinsic region ((i) poly-Si region) has a strong influence on the recombination current through the p(i)n diode and that this initially intrinsic region needs to be about 30 μm wide to sufficiently reduce the recombination across the p(i)n diode. Lateral and depth-resolved time of flight secondary ion mass spectrometry analysis shows that the high-temperature annealing step causes a strong lateral inter-diffusion of donor and acceptor atoms into the initially intrinsic region. This diffusion has a positive impact on the passivation quality at the c-Si/SiOx/i poly-Si interface and is thus essential for achieving an independently confirmed efficiency of 26.1% with 30 μm-wide initially intrinsic poly-Si regions.

Study on structural and optical properties of Mn-doped ZnO thin films by sol-gel method

For ZnO, doping transition metal is one of the powerful tools to improve its photoelectric performance. In this study, Mn-doped ZnO thin films with various thickness and different doping concentration were synthesized by low cost sol-gel method. We systematically investigated structural and optical properties of Mn-doped ZnO with different concentrations and film thickness. Research showed that with the increase of Mn doping concentration, the crystallization of ZnO decreased, and the preferred orientation was weakened. Moreover, the ultraviolet–visible (UV–Vis) absorption coefficient rose as the energy gap (Eg) decreases and Urbach energy (EU) increases). In the intrinsic emission region below 380 nm and in the defect emission region of 440–600 nm, Mn-doped 1.5% ZnO showed the strongest emission, then the excessive doping would reduce photoluminescence of ZnO. However, in the defect emissions region of 380–440 nm, pure ZnO showed highest emission that decreased gradually with the increase doping concentration. Meanwhile, as the increase of film thickness, the crystallization properties of ZnO were improved, but there were more cracks which resulted in the decrease of UV–vis absorption coefficient, the decrease of Eg and the increase of EU). Meanwhile, the intrinsic emission enhanced and the defect emissions decreased.

New Pathways of Mutational Change in SARS-CoV-2 Proteomes Involve Regions of Intrinsic Disorder Important for Virus Replication and Release.

The massive worldwide spread of the SARS-CoV-2 virus is fueling the COVID-19 pandemic. Since the first whole-genome sequence was published in January 2020, a growing database of tens of thousands of viral genomes has been constructed. This offers opportunities to study pathways of molecular change in the expanding viral population that can help identify molecular culprits of virulence and virus spread. Here we investigate the genomic accumulation of mutations at various time points of the early pandemic to identify changes in mutationally highly active genomic regions that are occurring worldwide. We used the Wuhan NC_045512.2 sequence as a reference and sampled 15 342 indexed sequences from GISAID, translating them into proteins and grouping them by month of deposition. The per-position amino acid frequencies and Shannon entropies of the coding sequences were calculated for each month, and a map of intrinsic disorder regions and binding sites was generated. The analysis revealed dominant variants, most of which were located in loop regions and on the surface of the proteins. Mutation entropy decreased between March and April of 2020 after steady increases at several sites, including the D614G mutation site of the spike (S) protein that was previously found associated with higher case fatality rates and at sites of the NSP12 polymerase and the NSP13 helicase proteins. Notable expanding mutations include R203K and G204R of the nucleocapsid (N) protein inter-domain linker region and G251V of the viroporin encoded by ORF3a between March and April. The regions spanning these mutations exhibited significant intrinsic disorder, which was enhanced and decreased by the N-protein and viroporin 3a protein mutations, respectively. These results predict an ongoing mutational shift from the spike and replication complex to other regions, especially to encoded molecules known to represent major β-interferon antagonists. The study provides valuable information for therapeutics and vaccine design, as well as insight into mutation tendencies that could facilitate preventive control.

Recent research progress of ferroelectric negative capacitance field effect transistors

Ferroelectric negative capacitance field effect transistors(Fe-NCFETs) can break through the so-called “Boltzmann Tyranny” of traditional metal oxide semiconductor field effect transistors and reduce the subthreshold swing below 60 mV/dec, which could greatly improve the on/off current ratio and short-channel effect. Consequently, the power dissipation of the device is effectively lowered. The Fe-NCFET provides a choice for the downscaling of the transistor and the continuation of Moore’s Law. In this review, the representative research progress of Fe-NCFETs in recent years is comprehensively reviewed to conduce to further study. In the first chapter, the background and significance of Fe-NCFETs are introduced. In the second chapter, the basic properties of ferroelectric materials are introduced, and then the types of ferroelectric materials are summarized. Among them, the invention of hafnium oxide-based ferroelectric materials solves the problem of compatibility between traditional ferroelectric materials and CMOS processes, making the performance of NCFETs further improved. In the third chapter, the advantages and disadvantages of Fe-NCFETs with MFS, MFIS and MFMIS structures are first summarized, then from the perspective of atomic microscopic forces the “S” relationship curve of ferroelectric materials is derived and combined with Gibbs free energy formula and L-K equation, and the intrinsic negative capacitance region in the free energy curve of the ferroelectric material is obtained. Next, the steady-state negative capacitance and transient negative capacitance in the ferroelectric capacitor are discussed from the aspects of concept and circuit characteristics; after that the working area of negative capacitance Fe-NCFET is discussed. In the fourth chapter, the significant research results of Fe-NCFETs combined with hafnium-based ferroelectrics in recent years are summarized from the perspective of two-dimensional channel materials and three-dimensional channel materials respectively. Among them, the Fe-NCFETs based on three-dimensional channel materials such as silicon, germanium-based materials, III-V compounds, and carbon nanotubes are more compatible with traditional CMOS processes. The interface between the channel and the ferroelectric layer is better, and the electrical performance is more stable. However, thereremain some problems to be solved in three-dimensional channel materials such as the limited on-state current resulting from the low effective carrier mobility of the silicon, the small on/off current ratio due to the leakage caused by the small bandgap of the germanium-based material, the poor interfacial properties between the III-V compound materials and the dielectric layer, and the ambiguous working mechanism of Fe-NCFETs based on carbon nanotube. Compared with Fe-NCFETs based on three-dimensional channel materials, the Fe-NCFETs based on two-dimensional channel materials such as transition metal chalcogenide, graphene, and black phosphorus provide the possibility for the characteristic size of the transistor to be reduced to 3 nm. However, the interface performance between the two-dimensional channel material and the gate dielectric layer is poor, since there are numerous defect states at the interface. Furthermore, the two-dimensional channel materials have poor compatibility with traditional CMOS process. Hence, it is imperative to search for new approaches to finding a balance between device characteristics. Finally, the presently existing problems and future development directions of Fe-NCFETs are summarized and prospected.

Electrical characteristics analysis of PIN detector with different doping concentration levels of N and P-type materials

Present work involves the analysis of electrical characteristics of PIN photodetector with different doping concentration of P and N-type regions which serve as good ohmic contacts. It is possible to improve the basic electronic properties of a PIN photodetector with slight changes in doping levels. So, critical investigation of limit of heavy doping levels of N and P-type materials is very important. Hence this paper illustrates the importance of selecting the optimum value of doping levels when the doping level of intrinsic region remains fixed. Moreover, it provides the analysis of cathode current, recombination rate; electric field; spectral and transient responses of PIN detector to highlight the effect of doping concentration below or beyond the optimum value (1018) for the selected detector. For large photocurrent and fast switching operation there is a need to define the optimum level of the doping concentration of P and N-type layers in PIN detector. In this paper, the performance of Silicon based PIN photodiode’s intensity response within 100–1000 nm wavelength range is demonstrated. The present work will be beneficial in different applications such as detection of light in Ultraviolet range and for high-speed switching circuits.

Physical insights into the effects of quantum dots size and temperature on efficiency of InAs/GaAs quantum dots intermediate band solar cell

The main problem of the photovoltaic conversion device is that low energy photons cannot excite charge carrier to the conduction band, so that the concept of the quantum dot solar cell is proposed in the intrinsic region of the p−i−n structure. In this work, numerical simulation has been proposed using the Matlab software. We simulate and measure the effects of quantum dots size and temperature on efficiency of GaAs p−i−n structure solar cells incorporating quantum dots (QDs) InAs under illumination. The results show that the efficiency of p−i−n solar cell depend strongly on size of QDs and temperature.

The Dynamic Emission Zone in Sandwich Polymer Light‐Emitting Electrochemical Cells

AbstractIn light‐emitting electrochemical cells (LECs), the position of the emission zone (EZ) is not predefined via a multilayer architecture design, but governed by a complex motion of electrical and ionic charges. As a result of the evolution of doped charge transport layers that enclose a dynamic intrinsic region until steady state is reached, the EZ is often dynamic during turn‐on. For thick sandwich polymer LECs, a continuous change of the emission color provides a direct visual indication of a moving EZ. Results from an optical and electrical analysis indicate that the intrinsic zone is narrow at early times, but starts to widen during operation, notably well before the electrical device optimum is reached. Results from numerical simulations demonstrate that the only precondition for this event to occur is that the mobilities of anions (μa) and cations (μc) are not equal, and the direction of the EZ shift dictates μc > μa. Quantitative ion profiles reveal that the displacement of ions stops when the intrinsic zone stabilizes, confirming the relation between ion movement and EZ shift. Finally, simulations indicate that the experimental current peak for constant‐voltage operation is intrinsic and the subsequent decay does not result from degradation, as commonly stated.

Antenna beam forming and beam controlling for Improving the Wi-Fi signal

Antenna design plays a prominent role when we consider the far-field patterns when compared with near field patterns. By using a PIN diode (which has a wide intrinsic region when compared with normal diode) as a switch and a capacitor as a filter we are proposing an antenna design that able to radiate far field regions. The reason behind choosing capacitor as a filter means that we are designing antenna to transfer high frequency signals. For antenna deign simulations we have different software’s (like FEKO, ZELAND IE 3D etc.,) but the preferred software for this antenna design is Computer Simulation Technology Microwave Studio (CST MWS) as we are operating in a frequency band of 2 to 2.54GHz and the diameter of the antenna 20X20cm. Based on the diameter chosen the antenna is able to switch direction of signalling by using a switch with four different angles. The material used for antenna design FR-4 which is a Composite material composed of fibre glass cloth with an epoxy resin blinder i.e. frame resistance and SMB connectors with 75Ω impedance.

Candidate for Magnetic Doping Agent and High-Temperature Thermoelectric Performance Enhancer: Hard Magnetic M-type BaFe12O19 Nanometer Suspension.

How to prevent the agglomeration of nanoparticles in nanocomposites remains a key challenge. Using nanometer suspension as a doping agent provides an effective approach to solve this challenge. A new technique that consists of chemical coprecipitation, ball milling and sedimentation separation metheds was developed for preparing hard magnetic M-type BaFe12O19 nanometer suspension. The single-phase BaFe12O19 nanoparticles dispersed uniformly in alcohol have been prepared by this new technique. Magnetic nanocomposite thermoelectric materials with a homogeneous dispersion of BaFe12O19 nanoparticles were prepared through a combination process of an ultrasonic mixing of BaFe12O19 nanometer suspension and In-filled CoSb3 thermoelectric matrix material and spark plasma sintering. The microstructure analysis of magnetic nanocomposite thermoelectric materials confirmed that using the nanometer suspension as a doping agent is an effective way to solve the agglomeration phenomenon of nanoparticles in nanocomposites. In addition, the decline of thermoelectric performance in the high-temperature intrinsic excitation region of In-filled CoSb3 can be effectively suppressed by the magnetic phase transition of BaFe12O19 nanoparticles dried by nanometer suspension from ferromagnetism to paramagnetism. It is also confirmed that using the BaFe12O19 nanometer suspension as a thermoelectric performance enhancer is an effective way to solve the challenging problem of performance deterioration of thermoelectric materials at high temperature.

Allosteric changes in HDM2 by the ATM phosphomimetic S395D mutation: implications on HDM2 function.

Allosteric changes imposed by post-translational modifications regulate and differentiate the functions of proteins with intrinsic disorder regions. HDM2 is a hub protein with a large interactome and with different cellular functions. It is best known for its regulation of the p53 tumour suppressor. Under normal cellular conditions, HDM2 ubiquitinates and degrades p53 by the 26S proteasome but after DNA damage, HDM2 switches from a negative to a positive regulator of p53 by binding to p53 mRNA to promote translation of the p53 mRNA. This change in activity is governed by the ataxia telangiectasia mutated kinase via phosphorylation on serine 395 and is mimicked by the S395D phosphomimetic mutant. Here we have used different approaches to show that this event is accompanied by a specific change in the HDM2 structure that affects the HDM2 interactome, such as the N-termini HDM2–p53 protein–protein interaction. These data will give a better understanding of how HDM2 switches from a negative to a positive regulator of p53 and gain new insights into the control of the HDM2 structure and its interactome under different cellular conditions and help identify interphases as potential targets for new drug developments.

GeSn/Ge Pin Diodes on Si with Sn Contents up to 14 %

We report about the fabrication of GeSn/Ge pin diodes with Sn concentrations between 8 % and 14 %. The thickness of the GeSn layers in the intrinsic region was 100 nm. Starting from 12 % Sn, the GeSn begins to relax, which is associated with a significant increase in dark current of the associated pin bulk diodes. In contrast, the same amount of Sn incorporated in multi quantum-well structures grows pseudomorphically. In these diodes the dark current is reduced by almost two orders of magnitude for the highest Sn concentration of 14 % compared to the pin bulk diodes with the same Sn concentrations.

InAs/GaAs quantum dot solar cells with quantum dots in the base region

In this work, the influence of quantum dot (QD) position on the performance of solar cells was studied. The presence of QDs within the base regions leads to improved open circuit voltage (Voc) from 0.73 to 0.90 V. Despite a slight reduction in short-circuit current (Jsc) due to carrier collection loss, the enhancement of the Voc of QDSCs with QDs in base region is significant enough to ensure that power conversion efficiencies (η) are higher than the reference quantum dot solar cell (QDSC) of which QDs are embedded in the intrinsic region. Moreover, sample with QDs in deep base region achieved the highest η of 9.75%, an increase of 29% with regard to the reference quantum dot solar cell.

Physics-Based Capacitance Model of Drift Region in Laterally Diffused Metal-Oxide Semiconductor and Its Implementation with BSIM4.

A physical capacitance model is presented for the drift region in a laterally diffused metal-oxide semiconductor (LDMOS). It is derived as a surface-potential-based model of nodal charge for the drift region. The model is combined with BSIM4, which is for the intrinsic MOSFET region of LDMOS, and it is validated with TCAD and measurement data. The model accurately predicts the capacitance of each node for the entire bias region.

A Dynamically Modulated All‐Dielectric Metasurface Doublet for Directional Harmonic Generation and Manipulation in Transmission

AbstractIn this paper, an electrically tunable all‐dielectric metasurface doublet is proposed operating at mid‐infrared frequency regime with dynamic 2π phase span in transmission mode. Each layer of the metasurface consists of a periodic array of silicon nanobars configured into p‐i‐n junctions in which the double carrier injection into the intrinsic region under forward bias allows for tuning of the silicon refractive index. The physical mechanism is based on the spectral overlap of high quality factor guided mode resonances supported by each constituent layer establishing an extreme Huygens' operation regime of nearly reflectionless transmission with steep phase spectrum. The short response time of field‐driven carrier injection in p‐i‐n junctions allows for modulation of refractive index with radio‐frequency biasing signals, yielding a stable time‐modulated all‐dielectric metasurface with directional frequency conversion and harmonic generation in transmission. A systematic approach is adopted to control the output spectrum of generated frequency harmonics through engineering the temporally modulated phase of transmitted light via adjusting the modulation waveform. Specifically, pure frequency mixing and concurrent dual‐frequency generation in transmission mode are demonstrated. Unique applications of the time‐modulated all‐dielectric metasurface are presented including wavelength‐multiplexed metalens for dual‐polarity focusing/diffusing and frequency diverse transmitarray for ultrafast spatiotemporal beam‐scanning.

Low-Power, High-Sensitivity Temperature Sensor Based on Ultrathin SOI Lateral p-i-n Gated Diode

In this work, we present a silicon-based p-i-n thermal diode, with post-CMOS MEMS processing (deep reactive ion etching and Al deposition) and annealing (at 250 °C). The MEMS processing degraded device stability as well as thermal sensing linearity and sensitivity, while the local annealing recovered the device performance (forward and reverse characteristics) by reducing the trap density and improving the carrier lifetime. After annealing, the on-membrane diode can achieve stabilized thermal linearity with a high sensitivity of ~ 2.25 mV/°C at 0.02– $0.03~\mu \text{A}$ low constant current, in the temperature range from room temperature to 200 °C, under a back-gate bias of 90 V to achieve a fully-depleted condition in the intrinsic (I) region and decrease the trap-assisted recombination at the front surface which dominates and degrades the device forward output current. To be compatible with commercial 1.0- $\mu \text{m}$ SOI CMOS technology, a front gate with a 25-nm-thick oxide dielectric is proposed and simulated in Atlas/SILVACO to optimize the device performance and achieve the same thermal characteristics under a front-gate bias of 1.0 V, showing its potential in low-power consumption electronics. The temperature sensor investigated in this work shows its industrial capability in gas sensing and integrated circuit applications.

An electrostatic analytical modeling of high-k stacked gate-all-around heterojunction tunnel FETs considering the depletion regions

This paper deals with the analytical modelling of high-k stacked Gate-All-Around Heterojunction Tunnel Field Effect Transistor (GAA-HJTFET) considering the depletion regions. The surface potential is derived from 2D Poisson’s Equation using the Parabolic Approximation Methodology and the Electric field is obtained by differentiating the surface potential. The drain current is obtained by considering volume of the device, shortest tunnelling path using the Kane’s Model. Due to heterojunction of the SiGe the energy band of the device move downwards to the intrinsic region because of which ION current improves, supress ambipolar behaviour of the device and reduces subthreshold swing. ION-IOFF ratio obtained from the device is 1010. Threshold voltage, transconductance is calculated using drain current equation where the threshold voltage is between 0.7 and 0.8 V and transconductance is 280 µA/mV. The results obtained are validated using ATLAS TCAD Simulation Tool.

Analytical Study of Performance Parameters of InGaN/GaN Multiple Quantum Well Solar Cell

An analytical study has been carried out to obtain the device performance parameters of InGaN/GaN-based multiple quantum well solar cell (MQWSC). Significant improvements are made upon the preexisting models reported in the literature for predicting device performance matrix for MQWSC. The American Society for Testing and Materials (ASTM) standards data sheets are utilized for attaining photon flux density instead of blackbody radiation formula. Furthermore, the photon flux density is utilized to evaluate the performance parameters of MQWSC and bulk p-i-n solar cell. Results suggest that by incorporating QWs in the intrinsic region ( ${x} = {0.1}$ in $\text{In}_{x}\text{Ga}_{{1}-{x}}\text{N}$ ), ∼27% increment in the conversion efficiency can be achieved as compared to that from the bulk solar cell. Moreover, the impact of operating temperature in the solar cell performance is also studied. The rise in temperature leads to an increase in short-circuit current density; however, open-circuit voltage and conversion efficiency decrease. A decrement of ∼9.7% in the conversion efficiency of MQWSC is observed with the rise in temperature from 200 to 400 K as compared to ∼11.6% decline in p-i-n solar cell.

Nonvolatile and Volatile Memory Characteristics of a Silicon Nanowire Feedback Field-Effect Transistor With a Nitride Charge-Storage Layer

We demonstrate the nonvolatile and volatile memory characteristics of a gate-all-around silicon nanowire feedback field-effect transistor (FBFET) with a nitride charge-storage layer analyzed by a commercial TCAD simulator. Our FBFET exhibits a threshold voltage window of 0.76 V with a programming/erasing time of ${1}~\mu \text{s}$ in the nonvolatile memory mode. We investigated the delay of read operations with accumulated charges in the intrinsic channel region in this memory mode. Moreover, the FBFET exhibits a sensing margin of 6.3 $\mu \text{A}$ and a read/write speed of 10 ns with an outstanding retention time, as well as nondestructive read characteristics in the volatile memory mode, allowing this device to operate without any refresh operation. In addition, we describe the operating principle of our device and demonstrate its potential as integrated memory for 3-D integrations.