Electrically Doped Research Articles

Controlling Drain Side Tunneling Barrier Width in Electrically Doped PNPN Tunnel FET

In this paper, we propose and investigate an electrically doped (ED) PNPN tunnel field effect transistor (FET), in which the drain side tunneling barrier width is effectively controlled to obtain a suppressed ambipolar current. We present that the proposed PNPN tunnel FETs can be realized without chemically doped junctions by applying the polarity bias concept to a doped N+/P- starting structure. Using numerical device simulations, we demonstrate how the tunneling barrier width on the drain side can be influenced by several design parameters, such as the gap length between the channel and the drain (Lgap), the working function of the polarity gate, and the dielectric material of the spacer. The simulation results show that an ED PNPN tunneling FET with an ED drain, which has been explored for the first time, exhibits a low ambipolar current of 5.87 × 10-16 A/µm at a gap length of 20 nm. The ambipolar current is reduced by six orders of magnitude compared to that which occurs with a conventional ED PNPN tunnel FET with a uniformly doped drain, while the average subthreshold slope and the ON state and OFF state currents remained nearly identical.

Spin transport properties in DNA & electrically doped iron QD organo-metallic junction

The DNA sensor has emerged as strong candidates for next generation ultra low power application due to its self assemble technique. Non-Equilibrium Green’s Function (NEGF) along with Density Functional Theory (DFT) based First Principle approach is used in investigation of spin transport properties along with quantum scattering transmission characteristics of DNA sensor via Iron (Fe) quantum dots (QD) electrodes at room temperature. Electrically doped Fe QD plays an important role in spin transport mechanism. This electrical doping concentration and weak coupling strength between DNA and Fe QD organo-metallic junction effect into the tunneling contact resistance (TCR) along with quantum-ballistic transmission and junction conductivity of parallel and anti-parallel configuration of this analytical model representation. It has been observed that higher current has been achieved for parallel configuration when compare with anti-parallel configuration at same bias voltage. This voltage-current characteristic is significantly modulated due to the electrical doping effect. This spin transport property shows that this system can well perform for anti parallel configuration. High tunnel organo-metallic resistance approximately 99.9% is observed even at 0 V bias voltage. Tunneling Organo Metallic Contact Resistance (TOMCR) remains large at upper bias voltage.

Sensitivity Analysis of Physically Doped, Charge Plasma and Electrically Doped TFET Biosensors

TFET based label-free biosensors are fast, sensitive and more power efficient as compared to CMOS biosensors, which are prone to short channel effects (SCEs). However, literature is flooded with various TFET biosensors that have become the reason of dilemma for researchers during pandemic situations like COVID-19. Therefore, in this work, a physically doped (PD), charge plasma (CP) and electrically doped (ED) dielectric modulated (DM) TFET based label-free biosensors are compared, which cover almost the entire range of doping and junctionless devices. Also, we found that the ED based TFET biosensors provide better current sensitivities of 5.10 × 107, 4.77 × 108 and 7.11 × 108 for biomolecules with K=12, positive charge= 1 × 1013 C/cm2 and negative charge= -1 × 1013 C/cm2 respectively. Hence, ED-DM-TFET based biosensors can act as promising candidates to provide better detection and identification quality.

Electrically doped SiGe-heterojunction TFET based biosensor considering non-ideal hybridization issues: a simulation study.

Calibrated simulations are used to study a dielectric modulated, electrically doped, dual metal gate, SiGe heterojunction, double gate TFET biosensor in this work. Use of lower bandgap SiGe at the source side helps in improving the ON current of the biosensor. Electric doping is preferred over physical doping to overcome the random dopant fluctuations and high thermal budget problems. Non-ideal situations having partially and non-uniformly filled cavity regions are analyzed in this work. Partially filled cavity has fill factor less than 100% and is studied by considering 50%, 20%, and 10% fill factors. Different positions of biomolecules inside a partially filled cavity are also studied through extensive simulations and are found to affect the sensitivity largely. Four different non-uniform profiles, decreasing, increasing, convex and concave, are created in the cavity region and their sensitivity values are compared for different dielectric constants (k) and charge densities (Q_{mathrm{Bio}}). Among the different non-uniform profiles considered, maximum sensitivity is obtained for decreasing profile and it improves with an increase in dielectric constant and positive charge density while it decreases when negative charge density increases.

Control of Water Adsorption via Electrically Doped Graphene: Effect of Fermi Level on Uptake and H2O Orientation

AbstractThe interaction of graphene with water molecules under an applied electric field is not thoroughly understood, yet this interaction is important to many thermal, fluidic, and electrical applications of graphene. In this work, the effect of electrical doping of graphene on water adsorption is studied through adsorption isotherms and current–voltage (IV) characterizations as a function of the Fermi level. The water adsorption onto graphene increases by ≈15% and the doping levels increase by a factor of three with a gate‐to‐graphene voltage of +20 or −20 V compared to 0 V for sub‐monolayer adsorption. This change in uptake is attributed to the increase in density of state of graphene upon electrical‐doping, which changes the Coulombic and van der Waals interactions. The water adsorption onto graphene is either n‐ or p‐doping depending on the applied gate‐to‐graphene voltage. The ambi‐doping nature of water onto graphene is due to the polar nature of water molecules, so the doping depends on the orientation of the water molecules.

Electron transport properties of electrically doped guanine nano-sheet based bio-Zener diode: a first principle paradigm

The quantum ballistic transmission properties of an electrically-doped guanine-nanosheet-based bio-Zener diode are investigated using density functional theory and nonequilibrium Green’s function-based first-principles calculations. The bio-Zener diode is gate-bias modulated, and its various quantum-electronic properties, for example, the V–I characteristic, the transmission spectra, and the device density of states, depend on both the electrical doping concentration and on the applied gate bias voltage. The junctionless highly doped bio-Zener diode shows high levels of reverse-bias current which is dominated by majority charge carriers. It is also found that, due to the presence of a wide bandgap and the backscattering effect, the forward-bias current is highly suppressed. The quantum simulation results confirm a strong reverse gate-bias-modulated biased current–voltage response as well as a charge transport phenomenon through the effective device region. The bio-Zener diode exhibits a specific reverse breakdown that can be varied from −0.78 to −3.2 V without affecting the forward current–voltage characteristic. The current findings are obtained by including the coherent tunneling and incoherent hopping processes with a minimal Hamiltonian model approach.

Charge generation efficiency of electrically doped organic semiconductors

Organic semiconductors (OSCs) have been a significant focus of research for electronic devices over the years exclusively due to their superior mechanical and optical properties as opposed to conventional inorganic semiconductors (ISCs) such as silicon or germanium. These unique materials have smoothened the path for developing extremely light-weight and ultrathin electronic devices with built-in flexibility and transparency for a considerably low cost. However, the commercial application of these organic materials is limited by their inferior electrical conductivity and charge carrier mobility compared with inorganic counterparts. This review article presents an overview of the works published on how to control and adjust the electrical conductivity of OSCs, focusing on electrical doping. The main point of this review is related to the principles and fundamental mechanisms of charge generation efficiency (CGE) in OSCs, which are significantly different from those of ISCs. The reported CGE of OSCs, defined as the ratio of the generated charge carriers to the dopants, is found to be in the range of a few percent and is significantly small compared with the ISCs. The origin of this lies in the lower dissociation rate of the charge transfer complexes (CTCs) formed between the tightly bound ionized dopants and generated charges. The CTCs induce localized electron-hole pairs, and the dissociation of such CTCs into free charge carriers requires large activation energies to overcome the strong Coulombic forces exerted on the generated charges by the dopant ions. Therefore, high doping concentrations are required to generate a large number of free charge carriers in doped OSC films. In this review, the CGE of OSCs is discussed in detail from the point of view of CTC formation and charge separation efficiencies.

Reactivity of an air-stable dihydrobenzoimidazole n-dopant with organic semiconductor molecules

Summary 1,3-Dimethyl-2-(4-(dimethylamino)phenyl)-2,4-dihydro-1H-benzoimidazole, N-DMBI-H, is widely used as an air-stable n-dopant for organic semiconductors. Here, its reactivity is investigated with a variety of imide- and amide-containing semiconductor molecules that have reduction potentials in the range −0.54 to −1.10 V versus ferrocene. Reaction rates correlate poorly with these potentials. The more reactive of the imides form the corresponding radical anions cleanly, but kinetic isotope studies using N-DMBI-D indicate that the reaction proceeds via an initial hydride- or hydrogen-transfer step. For an amide- and ester-rigidified bis(styryl)benzene derivative the hydride-reduced product is stable under an inert atmosphere and can be observed directly; the radical anion can only be obtained in sub-stoichiometric yield and under certain reaction conditions. On the other hand, (N-DMBI)2 rapidly reduces all the imides and amides examined to the corresponding radical anions. The implications of these findings for dopant selection and use are discussed.

Investigation of DC, RF and Linearity Performances of III–V Semiconductor-Based Electrically Doped TFET for Mixed Signal Applications

The aim of this paper is to bring forward a novel hetero-material electrically doped (ED) GAA TFET for high-performing and power efficient mixed signal applications. A number of low and high band gap III–V semiconductors were considered at source and drain channel regions, and their electrical characteristics were compared to identify the best alternative. To that end, DC/RF/linearity properties of AlGaSb/GaAsP, Ge/GaAs, Si/GaAs, Si/Ge, Silicon and SiGe/Si based ED GAA TFETs were analyzed. We found that the AlGaSb/GaAs-ED-TFET provides 16 $$\mu \hbox {A}$$ ON current at 25 mV/decade subthreshold swing and 1e13 $$I_{ON}/ I_{OFF}$$ ratio with exceptional analog and linearity characteristics. Also, we found that interface trap charges (ITC) in AlGaSb/GaAs-ED-TFET present negligible impact and have no effect on system performance. Further, improvisation is possible through mole fraction optimization of $$Al_{x}Ga_{1-x}Sb$$ . Finally, the mixed signal components that are widely available in system architectures are implemented using AlGaSb/GaAs-ED-TFET and their performance criteria are measured. All device simulations were performed using the TCAD Silvaco tool, and look-up based Verilog-A technique was used for circuit simulation in Cadence.

Efficient Electrical Doping of Organic Semiconductors Via an Orthogonal Liquid‐Liquid Contact

AbstractDoping is an effective strategy to tune the electrical properties of organic semiconductors. Traditional solution‐processed doping methods, including “host‐dopant mixing‐doping” and “post‐fabrication doping” methods, present challenges for their use in applications in optoelectronic devices. This work reports about a novel method to prepare electrically doped films, the authors call orthogonal liquid‐liquid‐contact (OLLC) doping. In OLLC doping, dopant and polymer semiconductors are dissolved in water and an organic solvent, respectively, and electrical doping occurs during film formation at the orthogonal liquid‐liquid (aqueous‐organic) interface. A large free volume of polymer and dopant in their solutions enables diffusion for effective doping. Thanks to the high surface tension of water, nanometer‐thick polymer films form spontaneously on the aqueous surface and simultaneously get doped. The doped thin polymer films on the aqueous surface can be easily transferred to devices to facilitate hole collection/injection in organic photovoltaics and light‐emitting diodes with solution‐processed top electrodes.

Electrical doping in single walled carbon nanotube systems: A new technique

First report on electrically doped semiconducting carbon nanotube is presented using Extended Huckel Theory in combination with Non-equilibrium Green’s function formalism. The results show increase in current with the increasing electrical doping concentration. Electrical doping induces high charge concentration at small applied voltages and is far more superior because of its fault free approach overcoming the limitations of conventional doping. Furthermore, the device density of states confirms the sufficient number of peaks in the valence and conduction bands. The obtained results were compared with other theoretical results in the field in the form of a table. The results are very beneficial for the designing of high-performance CNT devices and enhancing their potential applications in the electronics industry.

Electrothermal analysis of novel N-P-P FinFET with electrically doped drain: a dual material gate device for reliable nanoscale applications

In this paper, we offer a new structure of N+-P-P Fin Field Effect Transistor (FinFET) with a dual material gate in which the drain side P–N junction has been physically removed. The P-type drain consists of two parts, depletion region (DR) and electrically doped (ED) area, where the ED region is surrounded by an extra gate with optimized length and appropriate work function made of barium (B-gate). The ED region located under the B-gate is converted to N+ drain using the charged plasma (CP) concept to design the CP-FinFET. Improved ability to control the hot carrier effect by amending the critical electric field is the main idea of this work. The p-type depletion region (DR) created between the silicon active layer and electrically doped drain eliminates the gate-drain overlap and reduces the charge sharing and short channel effects (SCE). The modified electric field in the DR region offers advantages including improved hot-electron reliability and high-performance devices. Therefore, in the CP-FinFET the degradation mechanism improves due to the hot carrier effect (HCE) reduction. Indeed, the improvement in device performance is investigated using three-dimensional Atlas simulator with concentrating on the gate current, off-state current, reliability, electron temperature and gate induced drain leakage (GIDL). The comparison results demonstrate the superiority of the proposed structure as a high-efficiency device to design reliable Complementary metal–oxide–semiconductor circuits in nanoscale.

Metal-graphene hybrid active chiral metasurfaces for dynamic terahertz wavefront modulation and near field imaging

Chiral metasurfaces can achieve giant chiral optical responses and have been expanded from the optical band to other electromagnetic bands. Here, we propose a new method for dynamic terahertz circular dichroism (CD) manipulation in metasurfaces. By introducing a patterned and electrically doped graphene into the metamirror consists of double layer C-shaped split ring resonators (SRRs), efficient terahertz CD modulation is observed. Since the electrical doping of graphene changes the absorption loss of the metasuface cavity, the structure shows switching between a chiral metasurface and an ordinary metal mirror, which can be seen as "on" and "off" states. The calculation results show an efficient modulation of the terahertz CD in a large dynamic range. In addition, we also use the new method to design two metasurfaces for dynamic terahertz wavefront modulation and near-field digital imaging, both of which show a high-performance electrical switching. This method provides a new way for the design of active terahertz devices based on metasurfaces, and also promotes the applications of terahertz chiral metasurfaces in high-speed wireless communication and dynamic imaging.

Circuit Level Modeling of Electrically Doped Adenine–Thymine Nanotube Based Field Effect Transistor

We investigate the gate-controlled, electrically doped tunnelling current in Adenine-Thymine heterojunction nanotube-based Field Effect Transistor (FET). This analytical model FET is designed by Density Functional Theory (DFT) and Non-Equilibrium Green's Function (NEGF) based First principle formalisms. It is demonstrated that Band to Band Tunnelling (BTBT) is possible in relaxed Adenine-Thymine heterostructure nanotube. The evaluation of BTBT tunnelling probability to estimate tunnelling current for only ±0.01V applied bias voltage is calculated using Wentzel-Kramers-Brillouin approximation. Electrical doping is introduced to eliminate the probability of fault generation. By keen observation on the shift of energy levels in the band structure, the availability of high transmission co-efficient peaks and current-voltage response we demonstrate the Schottky barrier nature for this geometrically pre-optimized bio-molecular FET. The doping concentration is varied from 0.0001V to 0.1V to achieve a substantially large amount of tunnelling current when the electronic temperature is kept at 300K. The E-k diagram or complex band structure of this heterostructure nanotube ensures its in-direct semi-conducting nature. This is a first attempt to present a circuit-level demonstration using this Adenine-Thymine nanotube-based bio-molecular FET and validate the obtained results with the existing approaches.

Electronic transport properties of electrically doped cytosine‐based optical molecular switch with single‐wall carbon nanotube electrodes

This study represents an empirical model of cytosine-based optical molecular switch. This possible biomolecular switch has been designed using the first principle approach which is based on density functional theory and non-equilibrium Green's function. The quantum-ballistic transport property and current-voltage (I-V) characteristics of cytosine-based optomolecular switch have been investigated at 25 THz operating frequency. The influence of highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps on the electronic transmission and I-V characteristics has been discussed in detail. The aim of this study is to highlight the minimum conformational change during a single ON-OFF switching cycle. The biomolecule comprises switching behaviour when converts from straightened to twisted form during photo-excitement. The straightened and twisted forms of the molecule are represented as logic `0' and logic `1', respectively. This p and n regions of this switch has been made using electrical doping process. The current through the twisted form of the cytosine biomolecule is ~1000 times higher than the straightened form. The maximum switching ratio 62.1 is obtained at 1 V bias. The origin of the switching behaviour of the biomolecule can be interpreted by quantum-ballistic transport model along with HOMO-LUMO gaps.

Effective approach to enhance DC and high‐frequency performance of electrically doped TFET

The need to overcome the shortcomings of conventional tunnel field-effect transistor (TFET) has driven many to come up with advanced TFET innovations. This Letter presents a comparative analysis of new techniques to enhance DC/radio-frequency (RF) performance of dopingless TFETs. In this regard, two advanced structures have been compared along with conventional electrically doped TFET. The devices – electrically doped TFET, low work-function strip electrically doped TFET and low work-function live strip electrically doped TFET are investigated in terms of DC, RF and linearity. This Letter focuses on electrical doping on dopingless substrate to reduce random dopant fluctuations and fabrication complications. The comparative analysis illustrates the importance of low work-function live strip (LWLS) over low work-function strip (LWS). In addition, an optimisation of length and position of LWS and LWLS is also investigated for providing fabrication ease.

A first principle approach toward circuit level modeling of electrically doped gated diode from single wall thymine nanotube-like structure

This article presents a circuit level representation from gated diode which is developed from Thymine single wall nanotube-like structure using density functional theory and non-equilibrium Green’s function. Electrical doping process has been introduced to form the p and n region of this gated diode. This p–n junction diode is originated from the single wall Thymine bio-molecular nanotube-like structure. The atomically thin three-dimensional diode that can be realized from a single wall Thymine nanotube-like structure with optimum process step in 300 K. The operating frequency of this device is 1000 THz. The quantum-ballistic carrier transmission is analyzed using molecular projected self-consistent Hamiltonian and Hilbert space spanned basis functions quantum simulation process which ensures that this device acts as a diode and also shows strong non-linear current–voltage characteristics. Due to electrical doping process, no impurity or dopants are added externally to form p and n junction of the gated diode. A metallic gate has been incorporated to this theoretical model to vary the channel current of the diode. By varying the potential at the p and n side of the gated diode, the doping concentration can be varied. The 3.75 nm long and 1.42 nm wide Thymine single wall nanotube-like structure gated diode shows maximum 99.3 µA current at + 1 V applied bias voltage. This diode is used to implement the basic logic gates like AND, OR and NOR gate. First principle results and the available experimental results are therefore validated using atomistic simulation of the test bed molecules. These results suggested that this bio-molecular nano diode is capable for circuit level realization like implementation of logic gates and logic circuits, in high operating frequency oscillator, switches, memory devices etc. This theoretical study is an approach to implement circuit level modeling of molecules.

Atomic scale modeling of electrically doped p-i-n FET from adenine based single wall nanotube

The Field Effect Transistor (FET) characteristics has been observed from a single-walled Adenine nanotube device using Density Functional Theory associated with Non Equilibrium Green’s Function based First Principle approach. This device is electrically doped which shows both n and p channel characteristics of a p-i-n FET. This device is designed and originated from a single-walled biomolecular nanotube structure. The p and n regions have been induced at the two ends of the device using electrical doping process. Thus both n and p channel current-voltage response can be obtained within a single nano-scale device at room temperature operation. The device is 3.35nm long and 1.4nm wide. The quasi-ballistic quantum transmission property reveals impressive and almost ideal current-voltage characteristics of the FET. Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) gap reveals the possibility of quasi-ballistic coherent transmission of the device. The electronic properties based on Molecular Projected Self-consistent Hamiltonian are analyzed using Hilbert space spanned basis functions. The maximum tunneling current observed for the bio-molecular FET is 15.9μA for n-channel and 13.8μA for p-channel. The device is operated in atomic scale regime with 1000THz frequency. The present results reveal the role of quantum-ballistic tunneling phenomenon in the current-voltage characteristics and channel conductance properties of the bio nanotube structure, which is useful in future generation nano-electronics.

Controlling ambipolarity with improved RF performance by drain/gate work function engineering and using high $$\kappa $$ κ dielectric material in electrically doped TFET: proposal and optimization

This article proposes a novel device structure of electrically doped tunnel FET with drain/gate work function engineering by using hetero-dielectric material for the suppression of ambipolar behavior with improved DC and RF characteristics. For this, a P–I–N type structure was formed over an intrinsic silicon wafer by applying negative and positive voltages to create source and drain regions, respectively. Formation of source and drain regions by the concept of electrical doping is useful for reduction of random doping fluctuations and fabrication complexity. For suppression of ambipolar behaviour, the drain electrode is split into two different metal work functions ( $$\phi _\mathrm{DE1}$$ < $$\phi _\mathrm{DE2}$$ ), which alters the carrier concentration and increases the tunneling barrier at the drain/channel interface. Consequently, the proposed modification in terms of dual work functionality at the drain terminal offers better performance in terms of suppression of negative conductance (ambipolar current) and parasitic capacitances. However, the presence of dual work functionality at the drain electrode causes degradation in ON-state current and RF figures of merit. To resolve these problems, the control gate electrode is further split into two different work functions and uses hetero gate dielectric material, where the gate work function near the source/channel interface is greater than the gate work function near the drain/channel interface. It assists tunneling of carriers at the source/channel junction and improves ON-state current with RF performance. Apart from this, the use of hetero gate dielectric material provides further enhancement in DC and high frequency behaviour of the device.

Electronic characterisation of atomistic modelling based electrically doped nano bio p‐i‐n FET

In this study, electrically doped bio-molecular p-i-n field-effect transistor (FET) is designed and its electronic properties are investigated. Density functional theory along with non-equilibrium Green's function based first principle approach is used to design the bio-molecular FET at sub-atomic region. Three Adenine and two Thymine molecules are attached together to form 6.24 nm long and 1.40 nm wide bio p-i-n FET. This device is attached with two platinum electrodes and wrapped with a metallic cylindrical gate at high vacuum. Intrinsic n and p regions can be made possible within a bio-molecular device at room temperature by electrical doping without explicit dopants, which leads to conduct current by the device both in forward and reverse bias. The various quantum mechanical properties have been calculated using Poisson's equations and self-consistent function for the bio-molecular FET. Among these various quantum mechanical properties, the authors obtain high quantum transmission along with satisfactory current for the proposed device during the room temperature operation. The goal of this study is to highlight the design of a bio-molecular p-i-n FET with satisfactory large current using ultra low power dissipation.