Ge Mole Fraction Research Articles

Electrical characteristics of Si0.7Ge0.3/Si heterostructure-based n-type GAA MOSFETs

Electrical characteristics of Si0.7Ge0.3/Si heterostructure-based n-type gate-all-around MOSFETs (GAA MOSFETs) are reported in this work through experimental and numerical simulation data. N-type GAA MOSFETs of varying lengths (60 nm to 160 nm) and widths (20 nm to 42 nm) are fabricated and measured to extract key electrical parameters like ON current, ON-to-OFF current ratio, threshold voltage, DIBL, and subthreshold swing. Moreover, the influence of tensile strain on carrier transport parameters in the buried Si layer is examined in this work. The Ge mole fraction in SiGe is raised from 0.2 to 0.3, and the corresponding changes in XX-stress, and current density are analyzed using a TCAD simulator. The performance of the proposed device has also been compared with unstrained SiGe/Si, all Si, and SiGe-based GAA MOSFETs.

Sensitivity analysis of bi-metal stacked-gate-oxide hetero-juncture tunnel fet with Si0.6Ge0.4 source biosensor considering non-ideal factors.

This article provides insights in designing a dielectrically modulated biosensor by adopting high-k stacked gate oxide proposition in a bi-metal hetero-juncture Tunnel Field Effect Transistor (BM-SO-HTFET) with Si0.6Ge0.4 source. The integrated effect of heterojunction and stacked gate oxide leads to enhanced electrical performance of the proposed device in terms of carrier mobility and suppressed leakage current. Nano-cavity engraved beneath the bi-metal gate structure across the source/channel end acts the binding site of the biomolecules to be detected. This Configuration leads to improved control of biomolecules over source/channel tunnelling rate and the same is reflected in the sensing ability of the device while extracting the ON current sensitivity (SON) of the sensor. The reported biosensor is simulated using Silvaco ATLAS calibrated simulation framework. The analysis of the device sensitivity is carried out varying dielectric constants (k) of various biomolecules, both neutral as well as charged. Our study reveals that BM-SO-HTFET with Ge mole fraction composition x = 0.4 exhibits sensitivity as high as 4.1 × 1010 for neutral biomolecules and 3.2 × 1011 for positively charged biomolecules with k = 12. Furthermore, a transient response profile for the drain current with various biomolecules is explored to determine the varying settling time. From the simulation results, it is noted that BM-SO-HTFET exhibits ON current sensitivity of 4.1 × 1010 and 3.2 × 1011 for neutral and charged biomolecules respectively. In addition to this, for highly sensitive and real time detection of biomolecules, the impact of temperature and certain non-ideal factors drifting from ideal case of fully filled cavity have also been considered to analyze its optimum sensing performance.

Design and optimization of stress/strain in GAA nanosheet FETs for improved FOMs at sub-7 nm nodes

Stress/strain engineering techniques are employed to boost the performance of Gate-all-around (GAA) vertically stacked nanosheet field-effect transistors (NSFETs) for 7 nm technology nodes and beyond. In this work, we report on the 3D numerical simulation study of the impacts of source/drain epitaxial and uniaxial strained-SiGe channel stresses on p-type NSFETs. It is shown that the uniaxial strained-SiGe channel improves the drive current by up to 107% due to higher compressive stress while the 3-stack NSFET can achieve an enhancement in drive current even up to 187% using a 30% Ge mole fraction. Furthermore, we compare the multiple stacked channel NSFETs and nanowire FETs (NWFETs) considering different strain techniques. As compared to a 3-stack strained-SiGe NWFET, NSFETs show 27% and 10% enhancements in ION and SS, respectively. Vertically stacked NSFETs are shown to be the best option to improve the hole mobility under biaxial and uniaxial compressive strain rather than NWFETs. We also look at how the Ge mole fraction affects various electrical properties in a uniaxial strained-SiGe channel with shrinking dimensions of scaled NSFETs. It is observed that for a fixed Lg, ION/IOFF ratio, SS and DIBL decrease with the increase in Ge mole fraction.

A Simulation Study of SiGe Shell Channel CFET for Sub-2-nm Technology Nodes

In this article, a SiGe shell complementary FET (CFET) composed of an inversion mode (IM) nFET and a junctionless accumulation mode pFET under 2-nm (N2) and 1.5-nm (N1.5) technology nodes was studied for the characteristics of a single device and the CMOS logic circuit using 3-D numerical simulation. A comparison study between Si shell nanosheet and SiGe shell CFET with a Ge mole fraction in the range of 0.5–0.9. Compared with the Si shell nanosheet (NS), the SiGe shell CFET improves the ON-state current, transconductance, transition frequency, and intrinsic delay up to 29%, 32%, 31%, and 21%, respectively. Due to the mobility improvement in SiGe shell CFET, the fall time, rise time, propagation delay, and maximum operating frequency of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {Si}_{{0.5}}\text {Ge}_{{0.5}}$ </tex-math></inline-formula> shell CFET are also improved up to 2%, 43%, 3%, and 3%, respectively, compared with their Si shell counterparts. This SiGe shell CFET has a lower parasitic RC, a smaller layout area, and better analog and digital performance at the sub-2-nm technology node. This makes it a promising architecture for future high-performance CMOS logic applications.

Threshold Voltage Adjustment by Varying Ge Content in SiGe p-Channel for Single Metal Shared Gate Complementary FET (CFET).

We have demonstrated the method of threshold voltage (VT) adjustment by controlling Ge content in the SiGe p-channel of N1 complementary field-effect transistor (CFET) for conquering the work function metal (WFM) filling issue on highly scaled MOSFET. Single WFM shared gate N1 CFET was used to study and emphasize the VT tunability of the proposed Ge content method. The result reveals that the Ge mole fraction influences VTP of 5 mV/Ge%, and a close result can also be obtained from the energy band configuration of Si1-xGex. Additionally, the single WFM shared gate N1 CFET inverter with VT adjusted by the Ge content method presents a well-designed voltage transfer curve, and its inverter transient response is also presented. Furthermore, the designed CFET inverter is used to construct a well-behaved 6T-SRAM with a large SNM of ~120 mV at VDD of 0.5 V.

Compact Modeling of Forward Operation Band-to-Band andTrap-Assisted Tunneling Currents in SiGe HBTs

Band-to-band tunneling (BTBT) [1] and trap-assisted tunneling (TAT) [2] have been observed in the forward operation base current of SiGe HBTs [3], due to increasing emitter-base junction doping and decreasing bandgap from high Ge mole fraction. At present, a compact model for the BTBT base current in forward operation does not exist. The reverse bias BTBT current is modeled in Mextram for both emitter-base and collector-base junctions. A compact model of the forward TAT base current was developed by our group for wide temperature range operation [4]. In this work, we present a new compact model of BTBT and further develop the TAT compact model of [4] for commercial temperature range application, and demonstrate their effectiveness on SiGe HBTs with around 250 GHz peak fT and fmax.Fig. 1 shows measured IB-VBE characteristics at several temperatures, together with simulation using the latest version of Mextram, 505.3. VCB=0V. At moderate VBE, the IB-VBE slope starts to decrease, similar to high injection effect in diodes, when we know high injection has not occurred as IC-VBE slope remains its low injection value (not shown). Such behavior cannot be modeled with standard base current models. A newly developed neutral-base-recombination (NBR) model introduced in 505.3 is used to fit such high-injection like IB-VBE behavior [5]. In this work we focus on the low VBE regions. At VBE<0.2V, IB first increases, then decreases, exhibiting a negative differential resistance, which is due to BTBT [3]. This BTBT region shows very weak temperature dependence. IB then slowly increases, with a large non-ideality factor of 3.78, which we believe is due to TAT [2] [3] [4]. Note that this should not be confused with the depletion-region recombination current, called IB2 in Mextram [5], with an ideality factor close to 2. The corresponding saturation current in this “TAT” region shows a temperature dependence much weaker than what one expects from the depletion region recombination current as well.Our BTBT model is based on the approach of Esaki [1] and Karlovsky [6], and has a simple functional form: IB,BTBT = kBTBTVBE,btbt(VBE,btbt – VBTBT)2, KBTBT and VBTBT are model parameters that can be extracted from the IB peak position and slope of IB-VBE followed by optimization. VBTBT has a physical meaning of VBTBT =[(Efn-Ec)|n-side+(Ev-Efp)|p-side]/q, with all symbols having their usual meanings in PN junctions. VBE,btbt is a smoothly limited version of VBE for modeling BTBT. When VBE<0, VBE is smoothly limited to 0, i.e. VBE,btbt->0, so that it does not interfere with the existing reverse bias BTBT model. When 0<VBE< VBTBT, VBE,btbt is essentially equal to VBE by design except at the boundaries. When VBE>VBTBT, VBE is smoothly limited to VBTBT, so that the BTBT current decays to zero, as there will be no aligned available states for BTBT. We observe that the BTBT current is insensitive to temperature, consistent with [3], and find that no temperature scaling is necessary for modeling the BTBT current.The TAT current is modeled as ITAT = ISTAT(exp(VBE,tat/VTUN)-1), with VTUN and ISTAT as model parameters [4]. VBE,tat is approximately VBE when VBE>0, and smoothly becomes zero when VBE<0. ISTAT scales with temperature T according to ISTAT,T=ISTAT(T/Tref)1/2exp(kTAT(T-Tref)), where Tref is the reference temperature, and kTAT is a temperature scaling model parameter. VTUN is temperature independent.Fig. 2 shows the 25°C IB-VBE modeling result at low VBE using a linear current scale, to better illustrate the behavior of all IB components at low VBE. Fig. 3 shows a full range view on a logarithmic scale. Fig. 4 shows the modeling results at all four temperatures, with the insert showing the low bias details.Overall the proposed BTBT and TAT models do a good job fitting the forward operation IB-VBE characteristics, with an easy to use formulation, and a small number of model parameters, 2 for BTBT and 3 for TAT.

Impact on performance of dual stack hetero- gated dielectric modulated TFET biosensor due to Si1-xGex pocket variation

In this work, the performance evaluation of a dual stack hetero-gated pocket modulated tunnel FET (DSHGPM-TFET) based biosensor is presented. In the proposed device, cavity is formed by etching a portion of gate metal on both side of channel. The device contains a Si1-xGex pocket buried in the source region, where x (Ge mole fraction) is varied and effect on ION, VTH, and SS sensitivity is analyzed. The effect of x (=0, 0.4, 0.8, 1) and k (= 1, 5, 7, 10, 12) variation in DSHGPM-TFET is compared and noted. Also, the subthreshold swing (SS) and ION/IOFF ratio vs. dielectric constant at different x are plotted. Sensitivity is observed in the presence of neutral and charged (positive/negative) biomolecules within the cavity. Results show that increasing x of the pocket as well as k, enhances the sensitivity parameters. It is seen that sensitivity increases (decreases) with positive (negative) charged biomolecules. The work is further extended to study the performance of biosensor in non-ideal conditions. The effect of steric hindrance is studied by employing four different step profiles in cavity-concave, convex, decreasing, and increasing for two fill-factor (FF) 40% and 61%. The dynamic range of the proposed biosensor is estimated by varying x. Finally, the proposed sensor is compared with other biosensors existing in literature.

A comparative study on performance of junctionless Bulk SiGe and Si FinFET

In this paper, the n-type and p-type SiGe junctionless bulk FinFET (SiGe JL-FinFET) with a high Ge mole fraction (xF>0.8) was studied for characteristics of a single device and the CMOS logic circuit using 3D numerical simulation. A comparison study between SiGe JL-FinFET and Si JL-FinFET under 1×1019 to 5×1019 doping concentrations. The SiGe JL-FinFET exhibits a 28% and 9% enhancement of hole and electron mobility, thus the saturation current, transconductance, intrinsic gain, and intrinsic delay are improved up to 38%, 26%, 45% and 27% in the SiGe-based device as compared to the Si-based device. Due to the higher mobility and lower gate capacitance of SiGe JL-FinFET, the rise time, fall time, propagation delay, and maximum operating frequency of the CMOS inverter are also improved up to 34%, 13%, 9%, and 20%, respectively, compared to their Si-based counterparts. This SiGe junctionless device has a simple fabrication process and improvements in analog and digital performance at the sub-5 nm technology node, making this device a promising architecture for high-performance CMOS logic applications.

Exploring the performance of palladium gated – SiGe channel – Polarity controllable–FET for hydrogen gas monitoring applications

In the current work, a silicon-germanium (SiGe) channel-based Polarity Controllable FET (SiGe-PC-FET) has been investigated as a potential candidate in hydrogen gas sensing applications. The change in pressure of hydrogen gas molecules alters the work-function of Palladium gate metal which results in shift in electrical characteristics of the device. Further, the change in temperature along with mole-fraction of Ge in SiGe channel also plays a crucial role in determining the performance of gas sensor and thus, an exhaustive analysis in terms of various characteristics such as energy-band, surface potential, IDS – VCG and IDS – VDS has been carried out for a wide temperature range. Furthermore, the sensitivity analysis has been carried out in terms of drain-current, ION/OFF, transconductance and drain-conductance parameters at different pressures and temperatures. It has been demonstrated that even at elevated temperatures, the proposed gas sensor continues to offer improved sensitivity for a wide range of pressure values.

A single gate SiGe/Si tunnel FET with rectangular HfO2 dielectric pocket to improve I on/I amb current ratio

The ambipolar conduction in the tunnel field-effect transistors (TFETs) is considered the primary hindrance in its usage in complimentary digital circuits and low-power applications. The higher ambipolarity puts a serious question on the efficiency of a TFET, which is a result of channel/drain (C/D) tunneling. This further leads to a significant reduction in the current switching ratio (I on/I amb). This paper presents an n-type Si0.6Ge0.4/Si heterostructure TFET with a rectangular dielectric pocket (RDP) to maximize I on/I amb current ratio. This has been achieved by suppressing the ambipolarity and improving the on current simultaneously. The existence of Si1−x Gex in the source and silicon channel provides improved on current (I on) with controlled leakage current (I off). Similarly, high-k RDP in the drain reduces ambipolar current (I amb) significantly and thus, exhibits a higher I on/I amb ratio. The different parameters such as x-distance from the C/D interface, y-distance from the gate/drain interface, and dielectric constant has been considered to provide a higher I on/I amb ratio of . The effect of the presence of interface trap charges and variable Ge mole fraction has been studied. The current ratio can be further improved to with an underlap length of 25 nm.

Application of SiGe layer for reinforcing conductivity modulation in trench insulated gate bipolar transistor

In this work, an investigation for inserting a SiGe layer in an insulated-gate bipolar transistor (IGBT) has been performed to analyze the relation between on-state property and breakdown voltage (BV) with the help of technology computer-aided design simulation. For a carrier storage (CS) IGBT, which is widely studied for enhancing conductivity modulation by increasing hole density, the BV decreases by increased conductivity in the CS layer. However, by using the SiGe layer instead of the CS layer, the on-state property is improved with lower BV reduction than a CS IGBT due to the absence of impurity doping. Finally, an optimization for a Ge mole fraction is performed. Based on the results, it is found that the SiGe with 0.3 mole fraction shows the best performance because over 0.3 Ge mole fraction, the excessive energy band bending induced by over-accumulated holes makes low carrier velocity in the n-drift layer.

Effect of Ge Mole Fraction on Performance of Underlapped Gate-All-Around SiGe-Source Tunneling Field-Effect Transistors.

In this paper, we propose the design optimization of underlapped Si1-xGex-source tunneling field-effect transistors (TFETs) with a gate-all-around structure. The band-to-band tunneling rates, tunneling barrier widths, I-V transfer characteristics, threshold voltages, on/off current ratios, and subthreshold swings (SSs) were analyzed by varying the Ge mole fraction of the Si1-xGex source using a commercial device simulator. In particular, a Si0.2Ge0.8-source TFET among our proposed TFETs exhibits an on/off current ratio of approximately 1013, and SS of 27.4 mV/dec.

Performance Analysis of Planar Heterojunction Perovskite Solar Cell Featuring Double Hole Transport Layer &amp; Backplane

Perovskite photovoltaic cells have attracted appreciable importance from many researchers in the recent decade due to its reduced thickness, very less fabrication cost, and impressive photovoltaic performance. In this work, the authors investigated the simulation-based performance analysis of solar cells with perovskite CH3NH3PbI3 material. In the given paper authors have proposed the design of SnO2 (electron transport layer)/ CH3NH3PbI3 (active layer)/ SiGe and Spiro-OMeTAD (hole transport layers)/ SiGeSn (Backplane) based solar cell may be grown on the glass substrate. The simulation of the predicted device is compared with the already existing perovskite solar cell performance parameters and comparatively higher conversion efficiency was obtained for the proposed structure. In this proposed work, the consequence of perovskite layer thickness, different doping concentrations of perovskite (active) layer, hole transport layers (HTLs), Ge mole fraction of SiGe hole transport layer, hole mobility of Spiro-OMeTAD layer and backplanes on the characteristic performance of the proposed solar cell have been analyzed. The maximum conversion efficiency of 28.57% is reported for the given structure, having an amalgamation of two non-identical hole transport layers which ensures considerable photon conversion efficiency. Hence, this current work would propose a stepping stone in the advancement of high-performance perovskite photovoltaic cells in comparison with the pre-existing ones.

Design and Performance Analysis of Tunnel Field Effect Transistor With Buried Strained Si1−x Ge x Source Structure Based Biosensor for Sensitivity Enhancement

In this paper, a dielectrically modulated symmetrical double gate, having dual gate material, Tunnel Field-Effect transistor with Buried strained Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> source structure, has been investigated as a biosensor. This structure is proposed for the very first time to electrically detect the biological molecules at very low power consumption. In the proposed biosensor structure, the top thin Si channel of TFET is overlapped with the Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</sub> Ge <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> source. This increases the tunneling area, due to which ON current of the biosensor also increases. To detect the biomolecules a nanogap cavity has been created over 1nm gate oxide. Also to decrease the short channel effects, dual-gate material with different metal work functions is used on both the symmetrical double gates. By varying the small bandgap material (Ge) mole fraction in the SiGe and after inserting different biological molecules (of the different dielectric) in a cavity, the variation in transfer characteristic, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> current ratio, SS along with their sensitivity is studied. Also, to signify the presence of biomolecules in the cavity, the g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</sub> ratio as a sensing metric is studied under the sub-threshold region. Along with the fully filled biomolecules cavity, the partially filled cavity and the effect of a steric hindrance have also investigated in this paper with various non-uniform step patterns of biomolecules in the cavity. Because, in a more practical situation, the steric hindrance effect doesn't allow the cavity to be entirely filled. Also, this paper addresses the optimization of drain current sensitivity, by different cavity length with different source overlapping cavity.

Mapping vapor – solid distributions of silicon germanium chemical vapor depositions

A Thermodynamic analysis of Si1-xGex Chemical Vapor Deposition via SiH4 and GeH4 was conducted for a complete determination of the Vapor – Solid distribution of Ge mole fraction. Explicit Vapor – Solid distributions are achieved after an empirical adjustment of the Gibbs Free Energy of reactions. The chemical reaction behind the adjusted values are not clearly identified, but thermodynamic control of the elemental ratio of the deposited films is definitely demonstrated. Only three numbers are needed to achieve full knowledge of a distribution, the Gibbs Free Energy of reactions for the deposition of each element and the regular solution interaction parameter. The underlying laws necessary for the comprehension of semiconductor Vapor – Solid Distributions are thus completely known, and the only difficulty lays in the determination of the Gibb Free Energy of reactions needed for the successful mapping of the distribution.

Explicit Threshold Voltage Modeling Insight for Short Channel Characterization of a WFE Elliptical GAA Strained-Si MOSFET

This paper presents explicit analytical modeling of a gate all around (GAA) strained silicon metal-oxide-semicondutor field-effect transistor (MOSFET) with elliptical cross section by incorporating the popular gate work function engineering (WFE) concept of lateral mole fraction variation from source to drain end. Surface potential and threshold voltage formulation of the proposed structure based on a quasi-three-dimensional scaling equation have been introduced. The derived model is further used to investigate the short channel characteristics of the device in terms of hot carrier effect (HCE), drain-induced barrier lowering (DIBL), threshold voltage roll off (TVRO), and subthreshold slope. The impact of device parameter variation including gate oxide thickness, effective radius, channel doping concentration, germanium (Ge) mole fraction variation in the strained silicon channel along with applied gate to source and drain biases are evaluated on device performance to justify its efficiency in comparison to its single gate material (SM) MOSFET equivalent. Our analytical analysis is further validated by ATLAS-3D device simulated data to verify the precision of the derived model.

Low Noise Multiquantum Well DAR IMPATT Diodes Based On SiXGe1-X/Si

A Multiquantum Well (MQW) SixGe1-x/Si DAR (Double Avalanche Region) IMPATT (Impact Avalanche Transit Time) diode as a high power-high efficiency-low noise source at W-band is proposed in this paper. The RF power, conversion efficiency and noise of the device are optimized with respect to number of quantum wells and Ge mole fraction. The proposed device delivers peak power of 2.7 W, conversion efficiency of 7.5% and noise measure of 25 dB when the number of wells in the MQW structure is four and mole fraction of Ge is 0.3. The admittance plots of the device exhibit distinct negative conductance bands for three different (0.1, 0.2 and 0.3) mole fractions of Ge. An upward shift of optimum frequency is observed with increasing Ge mole fraction. The noise measure of the device decreases with increasing mole fraction of Ge and decreasing current.

Threshold Voltage Variations Induced by Si1-xGex and Si1-xCx of Sub 5-nm Node Silicon Nanosheet Field-Effect Transistors.

In this paper, we investigated the threshold voltage (Vth) variations in sub 5-nm node silicon nanosheet FETs (NSFETs) caused by Ge and C diffusion into NS channels using fully-calibrated 3-D TCAD simulation. Ge (C) atoms of Si1-xGex (Si1-xCx) source/drain (S/D) diffuse toward the NS channels in lateral direction in p-type (n-type) FETs, and Ge atoms of Si0.7Ge0.3 stacks diffuse toward the NS channels in vertical direction. Increasing Ge mole fraction of the Si1-xGex S/D in the p-type FETs (PFETs) causing increasing compressive channel stress retards boron dopants diffusing from the Si1-xGex S/D into the NS channels, thus increasing the Vth of PFETs (Vth, p). However, the Vth, p decreases as the Ge mole fraction of the Si1-xGex S/D becomes greater than 0.5 due to the higher valence band energy (Ev) of the NS channels. On the other hand, the Vth of n-type FETs (NFETs) (Vth, n) consistently increases as the C mole fraction of the Si1-xCx S/D increases due to monotonously retarded phosphorus dopants diffusing from the Si1-xCx S/D into the NS channels. On the other hand, the Vth, p and Vth, n consistently decreases and increases, respectively, as Si/Si0.7Ge0.3 intermixing becomes severer because both Ev and conduction band energies (Ec) of the NS channels become higher. In addition, the Vth, p variations are more sensitive to the Si/Si0.7Ge0.3 intermixing than the Vth, n variations because the Ge mole fraction in NS channels affects the Ev remarkably rather than the Ec. As a result, the Ge atoms diffusing toward the NS channels should be carefully considered more than the C diffusion toward the NS channels for fine Vth variation optimization in sub 5-nm node NSFETs.

Generation of empirical pseudopotentials for transport applications and their application to group IV materials

Empirical pseudopotentials (EPs) allow for accurate and efficient modeling of atomistic electron transport. Unfortunately, EPs are available only for a few materials and atomic configurations. Furthermore, EPs for nanostructures have historically been described using a variety of different parameterized forms. To compete with more general first-principles methods, we propose an automated workflow to generate EPs of a general form for any material and atomistic configuration. In particular, we focus on the generation of EPs for electron transport calculations, i.e., we provide an EP that accurately reproduces a reference band structure. To demonstrate the applicability of the proposed method, we generate the EPs to reproduce the band structure for bulk Si, Ge, 3C–SiC (zinc-blende polytype), 4H–SiC (hexagonal polytype), diamond, and hydrogen terminated ⟨100⟩ oriented Si and Ge thin films, calculated using first principles. In addition, using the generated EPs, along with the virtual crystal approximation, we demonstrate that our method reproduces accurately the band structure related properties of Si1−xGex alloy as a function of Ge mole fraction, x. As an application of our generated EPs, we perform ballistic quantum transport simulations of extremely scaled (≈0.6 nm wide), hydrogen terminated, ⟨100⟩ oriented Ge and Si gate-all-around nanowire field-effect transistors and compare their transfer characteristics.

Novel Analytical Model for Computing Subthreshold Current in Heterostructure p-MOSFET incorporating Band-To-Band Tunneling Effect

Subthreshold current for heterostructure pMOSFET is analytically explored as a function of applied bias for Si-SixGe1-x material system in presence of band-to-band tunneling. Threshold voltage of the structure is calculated considering body effect for different structural parameters, and mole fraction of Ge is chosen as 0.28 for that operating point where 2DEG is yet to be formed, and thus suitable for estimating subthreshold conduction. Using this optimum structure, BTBT effect is incorporated to measure the drain current for a range of source-to-gate voltage (VSG), and results suits in excellent with available experimental data for very low and higher values of source-to-drain voltage (VSD). Result is also computed in absence of tunneling effect, and drastic variation is observed which speaks in favor of our proposed model of subthreshold conduction. A monotonic decrease of subthreshold slope is observed with increase of VSG, which speaks for the optimum biasing criteria for operation of the device in order to minimize the leakage current. Results are in favor of applying the model for sub-22 nm FinFET or even sub-10 nm TFET devices.