Nonuniform Doping Research Articles

Impact of Non-Uniform Doping on the Reliability of Double Gate JunctionLess Transistor: A Numerical Investigation

This paper systematically studies the reliability of non-uniformly doped Double Gate Junctionless transistor using ATLAS TCAD simulation. The reliability analysis is mainly based on the understanding of Band-To-Band-Tunneling (BTBT) current, lattice temperature, drain conductance and gate leakage current. Presented results show that higher source/drain work-function is beneficial in reducing tunneling current (1 × 10−9 A to 4 × 10−11 A @ V gs = −1 V) but eventually it will also degrade electrostatic current significantly (∼3 order). Source/Drain length has also been varied during optimization and it has been observed that, shorter source drain extension region degrades the device reliability (i.e. higher magnitude of tunneling current (7 × 10−9 A @ V gs = −1 V for L S = L D = 5 nm)). Different doping profile considered for performance assessment are: uniform, step (i.e. low–low–high and high–high–low etc.) and different configurations of gaussian doping profile. Minimum variation in tunneling current with negative gate bias, i.e. ∼ 1 order has been seen from the device having uniform doping 1019 cm−3 but at the cost of significantly high off-state current (2 × 10−9 A @ V gs = 0 V) and tunneling current (2 × 10−8 A @ V gs = −1 V). Thus, instead of using uniform doping, step type profile (i.e. Case A) is the better choice which results in lower tunneling current (1 × 10−9 A @ V gs = −1 V), moderate lattice temperature (326) and better I on/I off ratio (243 × 108). Device lattice temperature has also been controlled by using step A doping profile even at the higher operating temperatures due to lower Self Heating Effect.

Formation of Highly Doped Nanostripes in 2D Transition Metal Dichalcogenides via a Dislocation Climb Mechanism.

Doping of materials beyond the dopant solubility limit remains a challenge, especially when spatially nonuniform doping is required. In 2D materials with a high surface-to-volume ratio, such as transition metal dichalcogenides, various post-synthesis approaches to doping have been demonstrated, but full control over spatial distribution of dopants remains a challenge. A post-growth doping of single layers of WSe2 is performed by adding transition metal (TM) atoms in a two-step process, which includes annealing followed by deposition of dopants together with Se or S. The Ti, V, Cr, and Fe impurities at W sites are identified by using transmission electron microscopy and electron energy loss spectroscopy. Remarkably, an extremely high density (6.4-15%) of various types of impurity atoms is achieved. The dopants are revealed to be largely confined within nanostripes embedded in the otherwise pristine WSe2 . Density functional theory calculations show that the dislocations assist the incorporation of the dopant during their climb and give rise to stripes of TM dopant atoms. This work demonstrates a possible spatially controllable doping strategy to achieve the desired local electronic, magnetic, and optical properties in 2D materials.

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.

Selective Area Regrowth Produces Nonuniform Mg Doping Profiles in Nonplanar GaN p–n Junctions

Nonplanar GaN p–n junctions formed by selective area regrowth were analyzed using pulsed laser atom probe tomography. Dilute Al marker layers were used to map the evolution of the p-GaN growth interface, enabling extraction of time-varying growth rates for nonpolar, semipolar, and polar surfaces from the trench edge to the center, respectively. The Mg dopant concentration is facet-dependent and varies inversely with the growth rate for the semipolar facets that grow rapidly away from the trench sidewalls. The negligible growth on the vertical sidewall of the trench coincides with an order of magnitude higher Mg concentration and substantial clustering of likely inactive dopants. A high Mg concentration is also observed near the regrowth interface of polar and semipolar planes, which we attribute to etching damage. We conclude that device fabrication processes employing selective area regrowth on nonplanar interfaces should consider both the spatial and temporal dependencies of growth rate that lead to nonuniform doping and explore growth conditions that could reduce variations in growth rate when nonuniform doping would adversely affect device performance.

Silicon non-uniformly doped nanotransistor biosensors

To implement effective biomedical diagnostics, it is important to evaluate the potential of non-uniformly doped silicon cylindrical field nanotransistors, which are comparable in size to biological nanoobjects. With such special engineering of the working region of the transistor, when high-doped zone is bordered by the source, and low-doped zone with drain, can significantly increase the sensitivity of the sensor, due to the fact that the gating mechanism of molecules associated on its surface, becomes more efficient due to the complete screening of carriers in the workspace. This improves the transistor's conductivity, which provides an acceptable electrical response. Research the detecting properties of longitudinally non-uniformly doped silicon transistor biosensors with cylindrical geometry, which function in the depletion mode, using computer modeling based on the developed mathematical model of the electric current of the transistor in the subthreshold mode, taking into account the requirements for conducting field experiments. Quasianalyticity model subthreshold current for silicon field-effect transistor with non-uniformly doping of the working area where high-doping zone bordered by the source and low-doping with drain, on the basis of analytical solution of 2D Poisson equation was designed. Several prototypes with different concentration conditions of doping between zones, ranging from three orders of magnitude to five times higher, were studied using the example of measuring the pH of solutions using computer modeling. In this case, the operating mode of biosensors was regulated by strobing the electrolyte. In all cases, the gating mechanism of molecules bound on the surface of sensors will be more effective due to the complete shielding of carriers in the working area. With a certain form of impurity concentration in the work area, it can potentially increase the sensitivity by a factor of ten and provide an acceptable level of response. Also, an important advantage of the non-uniformly doped sensors is their very low charge detection limit. It can be concluded that reducing the steepness of the sub-threshold characteristic is one of the main goals in the development of biosensors based on silicon field-effect transistors. And an effective approach is a special engineering of the working area of the transistor structure of the sensor, associated with its non-uniformly doping. The developed model and the results show that further optimization of the structure of silicon cylindrical field nanotransistor sensors can provide a significant improvement in their sensitivity, as well as obtain a reliable assessment of its limits, and serve as a factor for the development of equipment for biomedical diagnostics.

Atomically Smooth Graphene‐Based Hybrid Template for the Epitaxial Growth of Organic Semiconductor Crystals

AbstractAtomically thin 2D materials are good templates to grow organic semiconductor thin films with desirable features. However, the 2D materials typically exhibit surface roughness and spatial charge inhomogeneity due to nonuniform doping, which can affect the uniform assembly of organic thin films on the 2D materials. A hybrid template is presented for preparation of highly crystalline small‐molecule organic semiconductor thin film that is fabricated by transferring graphene onto a highly ordered self‐assembled monolayer. This hybrid graphene template has low surface roughness and spatially uniform doping, and it yields highly crystalline fullerene thin films with grain sizes >300 nm, which is the largest reported grain size for C60 thin films on 2D materials. A graphene/fullerene/pentacene phototransistor fabricated directly on the hybrid template has five times higher photoresponsivity than a phototransistor fabricated on a conventional graphene template supported by a SiO2 wafer.

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.

Effects of Hafnium Oxide on Surface Potential and Drain Current Models for Subthreshold Short Channel Metal–Oxide–Semiconductor-Field-Effect-Transistor

Surface potential and drain current models for a physically based double halo metal–oxide–semiconductor-field-effect-transistor (MOSFET) are reported. The proposed models have been established in sub-threshold mode of MOSFET operation. The depletion layer depth used in the pseudo two dimensional Poisson’s equation comprises the effect of two symmetrical pocket implantations at both the ends of the channel region. In this effort, improvement in the investigation is brought in by taking lateral asymmetric channel owing to non-uniform doping. The conventional silicon-dioxide (SiO2) material is replaced with a promising high-k dielectric material hafnium oxide (HfO2) to analyze the surface potential and drain current models. Analytical results have been compared using Synopsys technology computer aided design (TCAD). Excellent conformities between the analytical models and simulations are observed.

Liquids relax and unify strain in graphene

Solid substrates often induce non-uniform strain and doping in graphene monolayer, therefore altering the intrinsic properties of graphene, reducing its charge carrier mobilities and, consequently, the overall electrical performance. Here, we exploit confocal Raman spectroscopy to study graphene directly free-floating on the surface of water, and show that liquid supports relief the preexisting strain, have negligible doping effect and restore the uniformity of the properties throughout the graphene sheet. Such an effect originates from the structural adaptability and flexibility, lesser contamination and weaker intermolecular bonding of liquids compared to solid supports, independently of the chemical nature of the liquid. Moreover, we demonstrate that water provides a platform to study and distinguish chemical defects from substrate-induced defects, in the particular case of hydrogenated graphene. Liquid supports, thus, are advantageous over solid supports for a range of applications, particularly for monitoring changes in the graphene structure upon chemical modification.

Impact of non‐uniformly doped double‐gate junctionless transistor on the performance of 6T‐SRAM bitcell

This work substantiates the impact of Gaussian doping on the electrical performance of double gate junctionless field-effect transistor (DG-JLFET). To get a better understanding of the influence of non-uniform doping, the device is compared with uniform-doped DG-JLFET with various concentrations. The device is later used to demonstrate its usability in six-transistor static random access memory (6T SRAM) bitcell by studying the performance metrics, i.e. stability noise margin and write delay. A comparison of performance metrics is also given with uniformly doped DG-JLFET-based-6T SRAM. Improvement in static noise margin was observed with Gaussian doping without compromising with write access time.

Advancing layered cathode material's cycling stability from uniform doping to non-uniform doping

Dopant segregation induced precipitates can further improve the cycling stability of a P2-layered cathode due to the precipitation strengthening effect, which conceptually validates that non-uniform doping has big advantage over uniform doping.

Parameter Extraction for the PSPHV LDMOS Transistor Model

This paper details a robust parameter extraction flow for the PSPHV LDMOS transistor model. The procedure uses a global scaling parameter set and accounts for self-heating. We describe how to determine parameters associated with important physical effects specific to PSPHV: non-uniform lateral channel doping; the Kirk effect; internal drain voltage clamping; and the drain expansion effect. The method is verified on devices from different technologies. Verilog-A code for PSPHV is publicly available.

PSPHV: A Surface-Potential-Based Model for LDMOS Transistors

This article presents PSPHV, a surface-potential-based compact model for laterally diffused MOS (LDMOS) transistors. PSPHV includes a new drain voltage scaling technique that enables accurate modeling of saturation in transistors with nonuniform lateral doping; gate bias-dependent interface charge, which models the gradual channel turn- ON seen in devices with halo doping; internal drain bias clamping, which eliminates the capacitance spikes seen in most existing LDMOS models; and a new avalanche current model for the drift region that accounts for the Kirk effect. PSPHV models the drain expansion effect and diode reverse recovery and is verified against experimental data.

Heterobarrier Varactors with Nonuniformly Doped Modulation Layers

Optimum shape of the capacitance–voltage (C–V) characteristic is a critical parameter determining the efficiency of frequency multiplication in heterobarrier varactors (HBVs) operating in the millimeter and submillimeter frequency ranges. A numerical model for calculating the C–V characteristics and leakage currents of HBV heterostructures with arbitrary composition and doping profiles has been verified on the basis of published and original experimental data. A specially designed HBV heterostructure with three undoped InAlAs/AlAs/InAlAs barriers surrounded by nonuniformly doped n-InGaAs modulation layers has been grown by molecular beam epitaxy on InP substrate. Prototype HBVs manufactured using the proposed heterostructure demonstrated a nearly cosine shape of the C–V curve at bias voltages up to 2 V, increased overlap capacitance, and low leakage currents.

A Comprehensive Methodology to Evaluate Losses and Process Variations in Silicon Solar Cell Manufacturing

Novel, high-throughput metrology methods are used in this paper for detailed performance loss analysis of approximately 400 industrial crystalline silicon solar cells, all coming from the same production line. The characterization sequence combines traditional global cell measurements (e.g., current–voltage, Suns- ${V}_{\text{OC}}$ ) with camera-based cell imaging of voltage distribution and power dissipation from photoluminescence and lock-in thermography, respectively. Spatial variations in current collection are visualized using a high-speed external quantum efficiency and reflectance measurement technique. A nondestructive transfer length method (TLM) measurement technique is also implemented, featuring circular TLM structures hidden within the busbars of the cells. The variance of individual loss parameters and their impact on cell performance are quantified for this large group of cells. Based on correlations performed across parameters, recombination losses in the bulk and rear surface of the cell are shown to be the primary limiting factor for the cell efficiency. The nature of these distributions and correlations provide important insights about loss mechanisms in industrial solar cells, helping to prioritize efforts for optimizing the performance of the production line. Additionally, many of the parameters extracted from these techniques can be tied back to incoming material quality issues (e.g., poor bulk carrier lifetime, nonuniform wafer doping) and to individual unit processes (e.g., texturing, phosphorus diffusion, silicon nitride deposition, metallization), allowing the data to be used directly for process control in manufacturing. All of the datasets are made available for download.

Bulk Junctionless Transistor (JLT) with non-uniform doping: A high performance and scalable device

In this paper we have presented the non-uniformly doped bulk Junction less transistor (JLT) and investigated bulk-JLT and SOI-JLT with non-uniform doping in terms of its electrical performance parameters and short channel effects (SCEs) parameters comparatively. Effective thickness of channel depends on non-uniform doping distribution parameters and this affects the performance of bulk-JLT notably, however it is not so in case of SOI-JLT. The effect of non-uniform doping on electrical characteristics of JLTs (bulk and SOI) in terms of Subthreshold Slope (SS), ON-current, OFF-Current and ON/OFF current ratio has been investigated, and the non-uniformly doped bulk-JLT exhibits high ON/OFF ratio (109 for 20 nm Gate Length). Moreover, the non-uniformly doped bulk-JLT also shows improved short-channel effects (SCEs) parameters (such as Drain Induced Barrier Lowering, Threshold Voltage variations etc.) compared to SOI-JLT. Lastly, the effect of standard deviation, dielectric constant, substrate doping, and well biasing on the device performance are examined to further improve the performance of bulk-JLT independently.

Impact of uniform and non-uniform doping variations for ultrathin body junctionless FinFETs

In this paper, 3-D device simulations are performed to analyze the variations of uniform and non-uniformly (Gaussian) doped junctionless FinFETs. The impact of Fin width (Fw), Fin height (Fh), Channel length (Lg) and Gate Oxide (tox) on drain current, ION/IOFF ratio, subthreshold swing, Drain Induced Barrier Lowering (DIBL) of Si based Bulk Junctionless FinFETs is investigated. The results shows that the ION = 183μA/μm, IOFF = 4.449 × 10−5 μA/μm, is achieved for non-uniformly doping when compared to uniform doping configurations with ION = 102 μA/μm, IOFF = 3.05 × 10−5 μA/μm of junctionless FinFETs. Furthermore, the results also shows that non-uniformly doped junctionless FinFETs with fin width of 6 nm exhibits better DIBL of 22.5 mV/V and Subthreshold swing of 62.04 mV/decade than the uniform doped junctionless FinFET with DIBL of 80 mv/V and Subthreshold swing of 67.62 mV/decade. Thus, the non-uniformly doped junctionless FinFETs can effectively improve the performance of Junctionless FinFETs. In addition, to reduce the leakage current in bulk FinFETs effect of Punch-through Stop (PTS) layer, bulk doping concentration and body bias variations are studied. Finally, the 6T-SRAM circuit was implemented for JL-FinFETs and the results suggest that Gaussian doping JL-FinFETs strengthens the applicability of SRAM in the memory design.