Nonuniform Doping Profile Research Articles

Design and Analysis of Electrical Characteristics of 14nm SOI-based Trigate Gaussian Channel Junctionless FinFET

Planar MOSFETs are reaching their physical limits. To overcome the limitations and improve channel gate control, FinFET technology, which uses many gate devices, is a superior choice while lowering the size of planar MOSFETs even further. In this paper, 14nm Silicon-On-Insulator-based Trigate Gaussian Channel Junctionless FinFET is presented. The gate length of 14nm is considered along with an Equivalent Oxide Thickness of 1nm, 5nm as fin width, and the work function of the gate metal is 4.75eV. The device architecture has a non-uniform doping profile (Gaussian distribution) across the fin’s thickness. It is devised to address the effects of Random Dopant Fluctuations such as channel mobility degradation in Junctionless FinFET based devices. The impact of fin height (Fh), gate dielectric and spacer dielectric on the Drain Induced Barrier Lowering, Subthreshold Swing, drain current of GC-JLFinFET is analyzed. The results show that the Ion=101.5μA/μm and Ion/Ioff is 3.2×107 are obtained for the proposed device structure compared to the existing structure, which has Ion/Ioff of 1.1x107. Furthermore, the proposed design shows better efficiency in short channel characteristics, namely DIBL=25.3 mV/V, Subthreshold Swing=63.88 mV/dec and Transconductance =3.621×105 S/μm. Thus the Gaussian Channel-based FinFET architecture can provide optimum results for Junctionless-based FinFET devices.

Highly sensitivity Non-Uniform Tunnel FET based biosensor using source engineering

The manuscript proposes a novel dielectrically modulated Non-Uniform Tunnel FET based Biosensor for the detection of charged and neutral biomolecules. In this work, the reliability analysis of Dual Material Source based Non-Uniform Tunnel FET Biosensor has been performed. The design of Non-Uniform Tunnel FET and doping profile at the tunneling junction is accountable for the improved sensitivity. The response of the proposed biosensor has been analysed in terms of threshold voltage sensitivity, ON-OFF current ratio sensitivity and drain current sensitivity by using Sentaurus TCAD device simulator. The investigation includes analysis of neutral, positive and negatively charged Bio-analytes at immobilization layer for different cases of dielectrics. In case of positively charged Bio-analytes, it has been observed that the proposed biosensor can obtain the highest sensitivities of 100 mV, 7.9 × 106, 451 for threshold voltage, ON-OFF current ratio, and drain current sensitivities, respectively. Furthermore, the performance and reliability assessment of the biosensor have been considered using the appearance of steric hindrance in different patterns and temperature fluctuations in the wide range from 200 K to 400 K.

A numerical modeling approach to estimate the piezoresistance of diffused resistors with experimental validation

Silicon piezoresistive sensors have been widely used for many applications in recent decades. Monocrystalline silicon resistors are realized using an ion-implantation or a thermal diffusion process with a Gaussian or complementary error function profile. However, over the years, most researchers have neglected the doping concentration profile of the piezoresistor in the modeling stages resulting in erroneous responses that are far removed from experimental results of fabricated resistive sensors. In the present work, we propose a simulation approach to accurately estimate the piezoresistance of thermally diffused resistors with a non-uniform doping profile. We have modeled the diffused resistor as a parallel combination of several small slices, each having a unique piezoresistive coefficient. Three different slicing strategies were investigated to evaluate the impact of the piezoresistive coefficients, the electrical resistivity of the resistor slices, and the stress profile across the thickness of the resistor embedded in an accelerometer device. The cumulative impact of these parameters on the sensor’s overall sensitivity is evaluated. Further, we have also studied the influence of the accelerometer’s flexure thickness on the sensor’s sensitivity. It is observed from the simulation results that one of the slicing strategies with more slices at the surface of the resistor results in less than 1% error compared to the experimental results of an accelerometer device with a 60 µm flexure thickness.

New nanoscale band-to-band tunneling junctionless GNRFETs: potential high-performance devices for the ultrascaled regime

High-performance sub-10-nm field-effect transistors (FETs) are considered to be a prerequisite for the development of nanoelectronics and modern integrated circuits. Herein, new band-to-band tunneling (BTBT) junctionless (JL) graphene nanoribbon field-effect transistors (GNRFETs) endowed with sub-10-nm gate length are proposed using a quantum transport simulation. The nonequilibrium Green’s function (NEGF) formalism is used in quantum simulations considering the self-consistent electrostatics and the ballistic transport limit. The computational assessment includes the IDS–VGS transfer characteristics, the potential and electron density distributions, the current spectrum, the ambipolar behavior, the leakage current, the subthreshold swing, the current ratio, and the scaling capability. It is found that BTBT JL-GNRFETs can provide subthermionic subthreshold swings and moderate current ratios for sub-10-nm gate lengths. Moreover, a new doping profile, based on the use of lateral lightly n-type-doped pockets, is adopted to boost their performance. The numerical results reveal that BTBT JL-GNRFETs with the proposed doping profile can exhibit improved performance in comparison with uniformly doped BTBT JL-GNRFETs. In addition, the role of the length and n-type doping concentration of the pockets in boosting the device performance is also studied and analyzed while considering the scaling capability of such devices, revealing that low doping concentrations and long pocket lengths are useful for performance improvement. The merits of the BTBT JL-GNRFETs based on the proposed nonuniform doping profile, namely sub-10-nm scale, steep subthermionic subthreshold swing, low leakage current, and improved current ratio and ambipolar behavior, make them promising nanodevices for use in modern nanoelectronics and high-performance integrated circuits.

Investigation of NBTI Effect in P-Type Junctionless Transistor with Uniform and Graded Doping Profiles

This paper presents the reliability effect analysis of Negative Bias Temperature Instability (NBTI) in p-type junctionless transistor (JLT) under uniform and non-uniform doping profiles using Global TCAD Solution. The work compares the change in threshold voltage ( $$\Delta {Vth}$$ ) with the stress time and relaxation time for uniform and non-uniform doping profile in long and short channel p-type JLT. When negative Vgs and Vds are applied in the device, large number of interface traps are generated due to the dissociation of Si–H bonds along with the silicon-oxide interface. This results in the subsequent increase in the threshold voltage (Vth), thereby decreasing the driving capability and hence affects the device performance. Further, it is observed, increase in temperature causes more increase in the threshold voltage (Vth). This effect is due to breaking of more Si–H bonds, generating more interface traps. Simulation results after comparison shows that this change in $$\Delta {Vth}$$ under stress is more in non-uniform than in uniform p-type JLT, this is due to the fact that an increase of trap charges on uniform p-type JLT is less compared to non-uniform p-type JLT. It is also observed that short-channel devices are more prone to NBTI effect.

Sn doping of (010) β-Ga2O3 films grown by plasma-assisted molecular beam epitaxy

Sn doping of (010) β-Ga2O3 grown by conventional plasma-assisted molecular beam epitaxy (PAMBE) and via metal oxide catalyzed epitaxy (MOCATAXY) using a supplied indium flux during molecular beam epitaxy (MBE) growth was investigated. While high Sn concentrations were achievable over a range of growth conditions in conventional PAMBE, Sn doping less than 1019 cm−3 resulted in non-uniform doping profiles for constant Sn cell temperatures, as well as run-to-run variation in doping. Sn doping in MOCATAXY grown β-Ga2O3 allowed for sharp doping profiles and a wide range of donor concentrations from 3.9 × 1016 cm−3 to 2 × 1019 cm−3 and a maximum room temperature Hall mobility of 136 cm2/V s at 3.9 × 1016 cm−3. From temperature-dependent Hall measurements, Sn was found to have a relatively deep donor state at 77 meV below the conduction band edge. The samples showed low electron mobility at cryogenic temperatures, suggesting the existence of high background impurity levels in the MBE grown films and the need for impurity control in the oxide MBE growth environment.

Effect of doping profile variation on nanoscale cylindrical gate carbon nanotube field-effect transistor: a computational study using nonequilibrium Green’s function formalism

The scaling down of modern devices beyond 15 nm has faced major setbacks as it engendered short channel effects which were seemingly inexorable. One of the solutions proposed was to replace the conventional silicon channel with carbon nanotubes (CNTs), giving rise to the carbon nanotube field-effect transistor (CNTFET). CNTs provide unrivaled electrical and mechanical properties which make them an attractive alternative to silicon for channel materials. In this research work, a cylindrical gate CNTFET model is proposed, and its performance is studied and compared with existing experimental results. The performance of the device due to the variation in the doping profile of the source and drain is studied to realize a device that can manifest superior characteristics compared with existing devices. A model with a non-uniform doping profile is proposed that results in a significant reduction in leakage current. The characteristics upon which the performance is evaluated are the on/off current ratio (I ON/I OFF), subthreshold swing (SS), and threshold voltage. By adjusting various parameters, a device is constructed with I ON/I OFF of 4 × 106, SS of 63 mV dec−1 (approximately), and a threshold voltage of 0.45 V, which performs better than existing devices shown in the literature. All the simulations have been performed by employing the nonequilibrium Green’s function formalism with the self-consistent solution of the Schrödinger and Poisson equations.

Design and Performance Evaluation of Sub-10 nm Gaussian Doped Junctionless SOI and SELBOX FinFET

In this paper influences of uniform and non-uniform doping on the performance of SOI and SELBOX FinFET at gate length of sub-7 nm are evaluated. Junctionless devices require very heavy and uniformly doped very thin channel. It adversely affects the performance such as reduction in on-current, increased off-current, and degradation in short channel behavior. Due to technical limitations, the doping profile becomes non-uniform in the vertical direction. In this simulation studies we use Gaussian doping profile in the vertical dimension to get non-uniform doping profile. The simulations are performed using Silvaco TCAD. Firstly, the performance of uniformly doped SOI and SELBOX Transistors are analyzed and compared. Furthermore, non-uniformly doped SOI and SELBOX FinFETs are analyzed and compared. Comparison is done on the basis of parameters ION, IOFF, ION/IOFF ratio, DIBL, VTH, and SS etc. The simulation results show that the multi-gate structure with SELBOX technology gives best results under non-uniform doping profile.

Potential of crystals with a nonuniform doping profile for a Fe2+:ZnSe laser

Special nonuniform doping profiles are proposed for Fe2+:ZnSe crystals, which can increase the output energy of Fe2+:ZnSe lasers in comparison with those based on active elements with a uniform distribution of the doping agent. We present the simulation results for thermoelastic stresses and distortions of the optical density that arise in a Fe2+:ZnSe crystal during pulsed pumping, with the Fe distribution profile in the ZnSe crystal being nonuniform both along the optical axis and in the transverse direction. It is shown that the proposed doping profile provides a reduction in the thermo-optical distortions along the optical axis as well as suppression of parasitic lasing in the transverse direction.

An Analytical Subthreshold Swing Model for fully-depleted MOSFETs with vertical Gaussian profile fabricated on modified silicon-on-insulator wafers

The objective of this study is to present an analytical subthreshold swing model for fully-depleted metal-oxide semiconductor field-effect transistors (MOSFETs) with vertical Gaussian profile fabricated on modified Silicon-on-Insulator (SOI) wafers. Commercial SOI wafers are radiation hardened by Si+ implantation which creates interface traps at buried SiO2/Si interface. Considering that channel potential is affected by non-uniform doping profile combined with process- and radiation-induced traps, the model is derived based on effective conduction path effect. The proposed model is validated by comparing analytical results with numerical simulation data obtained by using commercially available Sentaurus technology computer-aided design. The model agrees well with experimental extractions of irradiated nMOSFETs. This model is believed to be able to provide better physical insight and understanding of total dose irradiated modified SOI MOSFET devices operating in subthreshold regime.

Junction‐less charge plasma TFET with dual drain work functionality for suppressing ambipolar nature and improving radio‐frequency performance

This work deals with a distinct concept to realise the junction-less tunnel field effect transistor (JL TFET) by creating the plasma of charges. The crux of this study is to reduce ambipolar conduction and to improve high-frequency figure of merits. To construct a JL TFET, initially P + silicon film is considered and then metal electrodes are used to form drain and channel region. The drain electrode is separated into two sections and the work function of section adjacent to channel is selected higher than the other section. This provides a non-uniform doping profile in the drain region creating large barrier at the drain/channel junction to prevent the ambipolar conduction. Ambipolarity is reduced to 1 × 10 -14 from 1 × 10 -8 at V gs = -1.5 V. The selection of work function and length of drain electrode adjunct to channel is crucial for optimising device performance. This optimisation provides information that work function >4.0 eV and length = 10 nm completely suppresses the ambipolarity which is around 1 × 10 -21 with little degradation in ON-current. The high work function for the section of drain electrode adjunct to channel provides lower gate-to-drain capacitance (~2.67 fF) and superior high-frequency responses. Furthermore, performance assessment at circuit level is done by implementing primary digital circuits as inverter and NAND logic with lookup table based Verilog-A model.

Drift Field Implementation in Large Pinned Photodiodes for Improved Charge Transfer Speed

We present a methodology for generating built-in drift fields in large photodiodes. With the aid of TCAD we demonstrate how non-uniform doping profiles can be implemented in a standard CMOS process using a single additional mask and controlled using the implant conditions and mask geometry. We demonstrate that the resulting doping profile creates a built-in drift field and simulates the effect of the drift field on the charge transfer speed. We show that implementing a drift field can improve charge transfer characteristics of the photodiode.

Total Ionizing Dose Response of Different Length Devices in 0.13 μm Partially Depleted Silicon-on-Insulator Technology**Supported by the Weapon Equipment Pre-Research Foundation of China under Grant No 9140A11020114ZK34147, and the Shanghai Municipal Natural Science Foundation under Grant Nos 15ZR1447100 and 15ZR1447200.

An anomalous total dose effect that the long length device is more susceptible to total ionizing dose than the short one is observed with the partially depleted silicon-on-insulator technology. The measured results and 3D technology computer aided design simulations demonstrate that the devices with different channel lengths may exhibit an enhanced reverse short channel effect after radiation. It is ascribed to that the halo or pocket implants introduced in processes results in non-uniform channel doping profiles along the device length and trapped charges in the shallow trench isolation regions.

Doping-induced carrier profiles in organic semiconductors determined from capacitive extraction-current transients

A method to determine the doping induced charge carrier profiles in lightly and moderately doped organic semiconductor thin films is presented. The theory of the method of Charge Extraction by a Linearly Increasing Voltage technique in the doping-induced capacitive regime (doping-CELIV) is extended to the case with non-uniform doping profiles and the analytical description is verified with drift-diffusion simulations. The method is demonstrated experimentally on evaporated organic small-molecule thin films with a controlled doping profile, and solution-processed thin films where the non-uniform doping profile is unintentional, probably induced during the deposition process, and a priori unknown. Furthermore, the method offers a possibility of directly probing charge-density distributions at interfaces between highly doped and lightly doped or undoped layers.

A new modeling approach for amorphous silicon passivated front contact for thin silicon solar cells

Thermal oxide (SiO2) and hydrogen-rich amorphous silicon (a-Si:H) interlayer at the front metal-silicon contact of thin silicon solar cells has been optimized based on a theoretical model. An analytical solution to the complete set of equations has been provided to highlighted the potential use and implications of the a-Si:H/SiO2 as a passivation coating at the front surface in crystalline silicon solar cells. The simple analytical expressions of the emitter reverse saturation current density and the photocurrent density were also obtained taking into account bulk recombination velocity and non-uniform doping profile. An optimum a-Si:H/SiO2 interlayer thicknesses were noted to enhance the collection of light-generated free carriers, which improves the efficiency of the short wavelength quantum. This is achieved by a drastic reduction in the effective recombination at the emitter upper boundary, a properly primarily responsible for the decrease in the emitter saturation current density. The findings indicated that the emitter region should be treated as an active layer because an optimum a-Si:H/SiO2 interlayer thicknesses at the front contact (W n,1 = 5 nm and δ = 14 A) give an improvement that can reach 3.6 mA/cm2 for the photocurrent density, 63 mV for the open-circuit voltage, and 3.95% for the cell efficiency.

Nanowire Kinking Modulates Doping Profiles by Reshaping the Liquid-Solid Growth Interface.

Dopants modify the electronic properties of semiconductors, including their susceptibility to etching. In semiconductor nanowires doped during growth by the vapor-liquid-solid (VLS) process, it has been shown that nanofaceting of the liquid-solid growth interface influences strongly the radial distribution of dopants. Hence, the combination of facet-dependent doping and dopant selective etching provides a means to tune simultaneously the electronic properties and morphologies of nanowires. Using atom-probe tomography, we investigated the boron dopant distribution in Au catalyzed VLS grown silicon nanowires, which regularly kink between equivalent ⟨112⟩ directions. Segments alternate between radially uniform and nonuniform doping profiles, which we attribute to switching between a concave and convex faceted liquid-solid interface. Dopant selective etching was used to reveal and correlate the shape of the growth interface with the observed anisotropic doping.

Analytical subthreshold current modeling of nanoscale ultra-thin body ultra-thin box SOI MOSFETs with a vertical gaussian doping profile

Based on the evanescent-mode analysis, an insightful study of the channel potential is performed for the nanoscale ultra-thin body ultra-thin box SOI MOSFETs with a vertical Gaussian doping. And a two-dimensional (2D) analytical subthreshold current model is presented. The front and the back channel subthreshold currents are effectively derived using the inversion layer current density model which takes the Gaussian doping into account. The accuracy of the model has been verified by 2D numerical device simulations using Sentaurus Technology Computer-Aided Design (TCAD) from Synopsys. The model provides a deep understanding and can be instrumental for the nanoscale ultra-thin body ultra-thin box SOI MOSFETs with a non-uniform doping profile operating in the subthreshold regime.

A Surface-Field-Based Model for Nanowire MOSFETs With Spatial Variations of Doping Profiles

We report a novel method to solve the nonlinear 1-D Poisson's equation for the gate-all-around (GAA) nanowire MOSFETs with nonuniform doping profiles. An algebraic rela- tion between the electric field and potential is identified to develop a surface-field-based compact model. Drain current is derived from the oxide-interface boundary condition to avoid the complicated surface-potential approach. As verified by the TCAD simulations, this analytic model is capable of continuously covering all operating regions of GAA nanowire MOSFETs with slowly varying doping profiles.

Sensors for ultra-fast silicon detectors

We report on electrical and charge collection tests of silicon sensors with internal gain as part of our development of ultra-fast silicon detectors. Using C–V and α TCT measurements, we investigate the non-uniform doping profile of so-called low-gain avalanche detectors (LGAD). These are n-on-p pad sensors with charge multiplication due to the presence of a thin, low-resistivity diffusion layer below the junction, obtained with a highly doped implant. We compare the bias dependence of the pulse shapes of traditional sensors and of LGAD sensors with different dopant density of the diffusion layer, and extract the internal gain.

New analytical models of subthreshold surface potential and subthreshold current of fully depleted short-channel silicon-on-insulator MOSFETs with halo or pocket implantation

New analytical models of the subthreshold surface potential, threshold voltage and subthreshold current of fully depleted (FD) silicon on insulator MOSFETs with halo or pocket implants are presented. The subthreshold surface potential model is based on the solutions of the quasi-two-dimensional (2D) Poisson’s equation, which rigorously satisfy the boundary conditions of the continuity of the potential and electric field in the lateral direction along the channel surface of halo MOS transistors. Closed-form model equations without any fitting empirical formula correctly and efficiently generate the surface potential distribution between the source and drain regions. The drain-induced barrier lowering effect of deep-submicrometer halo MOSFETs is also addressed in the present models. On the basis of the subthreshold surface potential, analytical models of the threshold voltage and subthreshold current are also developed for deep-submicrometer halo MOSFETs. The subthreshold current model is derived using the conventional drift-diffusion current theory considering the nonuniform doping profiles of a silicon film of fully-depleted silicon-on-insulator (SOI) MOS devices with halo implants. The results obtained using the model have been compared with those obtained using the device simulation software Medici to show the validity of the proposed model, and good agreement is achieved between the two. The use of the presented models can be treated as an alternative to 2D numerical analysis and used for the design of deep-submicrometer FD SOI MOSFETs with halo or pocket implants.