Analysis of charge density and Fermi level of AlInSb/InSb single-gate high electron mobility transistor

A compact model is proposed to derive the charge density of the AlInSb/InSb HEMT devices by considering the variation of Fermi level, the first subband, the second subband and sheet carrier charge density with applied gate voltage. The proposed model considers the Fermi level dependence of charge density and vice versa. The analytical results generated by the proposed model are compared and they agree well with the experimental results. The developed model can be used to implement a physics based compact model for an InSb HEMT device in SPICE applications.     

Modeling and simulation of enhancement mode p-GaN Gate AlGaN/GaN HEMT for RF circuit switch applications

An enhancement mode p-GaN gate AlGaN/GaN HEMT is proposed and a physics based virtual source charge model with Landauer approach for electron transport has been developed using Verilog-A and simulated using Cadence Spectre, in order to predict device characteristics such as threshold voltage, drain current and gate capacitance. The drain current model incorporates important physical effects such as velocity saturation, short channel effects like DIBL (drain induced barrier lowering), channel length modulation (CLM), and mobility degradation due to self-heating. The predicted I_d-V_ds, I_d-V_gs, and C-V characteristics show an excellent agreement with the experimental data for both drain current and capacitance which validate the model. The developed model was then utilized to design and simulate a single-pole single-throw (SPST) RF switch.     

An accurate polynomial-based analytical charge control model for AlGaN/GaN HEMT

A new nonlinear expression of Fermi-level variation with two-dimensional electron gas density in a high electron mobility has been proposed. It was found that our expression has a better fit with the numerical results. And, an analytical expression for n _s in terms of the applied gate voltage is developed. Comparing with other previous approximations, the solutions of our expression has a better agreement with the exact numerical results over the entire range of interest. Besides, the solutions of our expression of n _s versus V _G are compared with the experimental data and shown to be in good agreement over a wide range of bias conditions.     

Analytical modeling and parameter extraction of top and bottom contact structures of organic thin film transistors

This paper proposes a structure based model of an organic thin film transistor (OTFT) and analyzes its device physics. The analytical model is developed for the top contact structure by mapping the overlap region to the resistance (in the vertical direction) that includes the contact and the bulk sheet resistances. Total device resistance includes the vertical resistance per unit area of the contact region and the sheet resistance of the channel. In addition, the drain and the gate voltages take into account the potential drop across the respective contacts. The gate bias dependent mobility is considered in place of constant mobility, since; it is more realistic and relevant to the organic TFTs. The proposed analytical model is also applied to the bottom contact structure and the current–voltage (I–V) characteristics are obtained. Furthermore, a differential method is employed to extract the parameters, such as, mobility enhancement factor γ, threshold voltage V_T, mobility µ_B, characteristic length L_C, vertical resistance R_V and contact resistance R_C. Finally, the model is validated in terms of electrical characteristics and performance parameters for both top and bottom contact structures. The analytical model results are in close agreement with the experimental results.     

Flicker and thermal noise in an n-channel underlap DG FinFET in a weak inversion region

We propose an analytical model for drain current and inversion charge in the subthreshold region for an underlap DG FinFET by using the minimum channel potential method,i.e.,the virtual source.The flicker and thermal noise spectral density models are also developed using these charge and current models expression.The model is validated with already published experimental results of flicker noise for DG FinFETs.For an ultrathin body,the degradation of effective mobility and variation of the scattering parameter are considered.The effect of device parameters like gate length L_g and underlap length L_un on both flicker and thermal noise spectral densities are also analyzed.Increasing L_g and L_un,increases the effective gate length,which reduces drain current,resulting in decreased flicker and thermal noise density.A decrease of flicker noise is observed for an increase of frequency, which indicates that the device can be used for wide range of frequency applications.     

DC and microwave characteristics of Lg 50 nm T-gate InAlN/AlN/GaN HEMT for future high power RF applications

The DC and microwave characteristics of L_g = 50 nm T-gate InAlN/AlN/GaN High Electron Mobility Transistor (HEMT) on SiC substrate with heavily doped n+ GaN source and drain regions have demonstrated using Synopsys TCAD tool. The proposed device features an AlN spacer layer, AlGaN back-barrier and SiN surface passivation. The proposed HEMT exhibits a maximum drain current density of 1.8 A/mm, peak transconductance (g_m) of 650 mS/mm and ft/fmax of 118/210 GHz. At room temperature, the measured carrier mobility, sheet charge carrier density (n_s) and breakdown voltage are 1195 cm²/Vs, 1.6 × 10¹³ cm⁻² and 18 V respectively. The superlatives of the proposed HEMTs are bewitching competitor for future monolithic microwave integrated circuits (MMIC) applications particularly in W-band (75–110 GHz) high power RF applications.     

Thermal model for dc characteristics of algan/gan hemts including self-heating effect and non-linear polarization

A thermal model based on the polynomial relationship of n_s and E_F is presented. The effect of temperature rise due to self-heating is studied on various parameters viz. polarization, electron mobility, velocity saturation, low-field mobility and thermal conductivity of substrate. Parasitic resistances and channel length modulation were also taken into consideration. The relationship between self-heating effect and device parameters was studied. The model is based on closed-form expressions and does not require elaborate computation. After including self-heating effect in calculations of current–voltage characteristics, our results agreed well with published experimental data.     

Performance analysis of long Ge channel double gate (DG) p MOSFETs with high-k gate dielectrics based on carrier concentration formulation

In this paper, electrical behavior of symmetric double gate Ge channel MOSFETs with high-k dielectrics is reported on the basis of carrier concentration formalism. The model relies on the solution of Poisson-Boltzmann equations subject to suitable boundary conditions taking into account the effect of interface trap charge density (D_it) and the Pao-Sah’s current formulation considering field dependent hole mobility. It is continuous as it holds good for sub-threshold, weak and strong inversion regions of device operation. The proposed model has been employed to calculate the drain current of DG MOSFETs for different values of gate voltage and drain voltage along with various important device parameters such as transconductance, output conductance, and transconductance per unit drain current for a wide range of interface trap charge density, equivalent oxide thickness (EOT) and bias conditions. Moreover, most of the important device parameters are compared with their corresponding Si counter parts. Accuracy of the model has been verified by comparing analytical results with the numerical simulation data. A notable improvement of the drive current and transconductance for Ge devices is observed with reference to Si devices, particularly when D_it is small.     

An analytical model for discretized doped InAlAs/InGaAs heterojunction HEMT for higher cut-off frequency and reliability

In the proposed work the model has been formulated for discretized doped HEMT, where the conventional uniformly doped, pulsed doped and delta doped structure are the special cases. An expression for sheet carrier density has been formulated considering the effect of doping-thickness product and has been extended to calculate drain current, transconductance, capacitance and cut-off frequency of the device. The model also takes into account the non-linear relationship between sheet carrier density and quasi Fermi energy level to validate it from subthreshold region to high conduction region. The results so obtained have been compared with pulsed doped structure to validate the model. The analysis concentrates on the distance of doping from the heterojunction and gate electrode. Different design criteria have been given to dope the carriers (amount and distance) in different regions to optimize the performance for higher sheet carrier density/parallel conduction voltage/effective parallel conduction voltage (V_c−V_off) to increase the transconductance, cut-off frequency and reliability of the device.     

Modeling on oxide dependent 2DEG sheet charge density and threshold voltage in AlGaN/GaN MOSHEMT

We have developed a physics based analytical model for the calculation of threshold voltage, two dimensional electron gas (2DEG) density and surface potential for AlGaN/GaN metal oxide semiconductor high electron mobility transistors (MOSHEMT). The developed model includes important parameters like polarization charge density at oxide/AlGaN and AlGaN/GaN interfaces, interfacial defect oxide charges and donor charges at the surface of the AlGaN barrier. The effects of two different gate oxides (Al₂O₃ and HfO₂) are compared for the performance evaluation of the proposed MOSHEMT. The MOSHEMTs with Al₂O₃ dielectric have an advantage of significant increase in 2DEG up to 1.2×10¹³ cm^-2 with an increase in oxide thickness up to 10 nm as compared to HfO₂ dielectric MOSHEMT. The surface potential for HfO₂ based device decreases from 2 to -1.6 eV within 10 nm of oxide thickness whereas for the Al₂O₃ based device a sharp transition of surface potential occurs from 2.8 to -8.3 eV. The variation in oxide thickness and gate metal work function of the proposed MOSHEMT shifts the threshold voltage from negative to positive realizing the enhanced mode operation. Further to validate the model, the device is simulated in Silvaco Technology Computer Aided Design (TCAD) showing good agreement with the proposed model results. The accuracy of the developed calculations of the proposed model can be used to develop a complete physics based 2DEG sheet charge density and threshold voltage model for GaN MOSHEMT devices for performance analysis.     

Comparison of two 1f noise models in MOSFETs

The noise expressions for the number fluctuation model and for the mobility fluctuation model of $\text{1}\text{f}$ in MOSFETs at low drain bias are derived and expressed in terms of the effective trap parameter [N_T(E_f)]_eff/? and in Hooge's parameter α_H, respectively. It is indicated how the turn-on voltage V_T of the device and the carrier mobility μ can be evaluated from the characteristics; the two parameters can then be determined from the measured drain noise. Both parameters have modest values; either model might be correct, but the present measurements cannot discriminate between the models. Silicon on sapphire MOSFETs have values for these parameters that are a factor 200 larger than other devices.     

Edge inversion channels and surface leakage currents in high-voltage semiconductor devices

It is shown that the electric field over the surface of semiconductor devices can be sufficient to induce edge inversion channels if the bias voltage is high and the surface charge density Q _s is low. In this case, the edge region of the devices containing the p-n-p structure (e.g., that of thyristors) functions as a planar p-channel MIS transistor with a combined gate and drain and the entire medium over the surface functions as the gate insulator. The current between the source and drain of this “edge MIS transistor” is the surface leakage current of the entire device. An analytical theory describing the current-voltage characteristic in the subthreshold mode is developed. It is shown that this new mechanism controls the total leakage current of high-voltage devices if |Q _s | and temperature T are small enough (|Q _s | < 4 nC/cm², T < 270 K and |Q _s | < 58 nC/cm², T < 600 K for silicon and silicon carbide devices, respectively).     

考虑量子效应的超薄体双栅肖特基源漏MOSFET电流解析模型

推导了超薄体双栅肖特基势垒MOSFET器件的漏电流模型,模型中考虑了势垒高度变化和载流子束缚效应.利用三角势垒近似求解薛定谔方程,得到的载流子密度和空间电荷密度一起用来得到量子束缚效应.由于量子束缚效应的存在,第一个子带高于导带底,这等效于禁带变宽.因此源漏端的势垒高度提高,载流子密度降低,漏电流降低.以前的模型仅考虑由于镜像力导致的肖特基势垒降低,因而不能准确表示漏电流.包含量子束缚效应的漏电流模型克服了这些缺陷.结果表明,较小的非负肖特基势垒,甚至零势垒高度,也存在隧穿电流.二维器件模拟器Silvaco得到的结果和模型结果吻合得很好.     

Base transit time of a bipolar transistor considering field dependent mobility

An empirical expression for the base transit time, τ_b , of a bipolar transistor with exponential base doping profile is derived considering doping and field dependence of mobility. In the analysis, bandgap-narrowing effect, high injection effect and carrier velocity saturation at the base edge of the collector-base junction are also incorporated. The collector current density, J_c , and minority carrier stored charge, Q_b , in the base are separately expressed as a function of the injected electron density n_o in the base in order to find an empirical expression for τ_b . The modelling of J_c , Q_b and τ_b is essential for the design of a modern bipolar transistor. The base transit time calculated analytically is compared with simulation and numerical results in order to demonstrate the validity of the assumptions made in deriving the expression. The base transit time is found to be different if the field dependent mobility is considered.     

Photophysics of Molecular‐Weight‐Induced Losses in Indacenodithienothiophene‐Based Solar Cells

The photovoltaic performance and optoelectronic properties of a donor–acceptor copolymer are reported based on indacenodithienothiophene (IDTT) and 2,3‐bis(3‐(octyloxy)phenyl)quinoxaline moieties (PIDTTQ) as a function of the number‐average molecular weight (M_n). Current–voltage measurements and photoinduced charge carrier extraction by linear increasing voltage (photo‐CELIV) reveal improved charge generation and charge transport properties in these high band gap systems with increasing M_n, while polymers with low molecular weight suffer from diminished charge carrier extraction because of low mobility–lifetime (μτ) product. By combining Fourier‐transform photocurrent spectroscopy (FTPS) with electroluminscence spectroscopy, it is demonstrate that increasing M_n reduces the nonradiative recombination losses. Solar cells based on PIDTTQ with M_n = 58 kD feature a power conversion efficiency of 6.0% and a charge carrier mobility of 2.1 × 10^?4 cm² V^?1 s^?1 when doctor bladed in air, without the need for thermal treatment. This study exhibits the strong correlations between polymer fractionation and its optoelectronics characteristics, which informs the polymer design rules toward highly efficient organic solar cells.     

Low frequency noise characterization in 0.13 μm p-MOSFETs. Impact of scaled-down 0.25, 0.18 and 0.13 μm technologies on 1/f noise

This paper presents an experimental analysis of the noise measurements performed in 0.13 μm technology p-MOS transistors operating from weak to strong inversion in ohmic and saturation regimes. The 1/f noise origin is interpreted in terms of carrier number with correlated mobility fluctuations. The contribution of the access resistance noise is noticed for large overdrive voltages. The slow oxide trap density N_t(E_F) and the Coulomb scattering noise parameter α_s have been extracted. Then the 1/f noise level in the three scaled-down p-MOSFETs generations (0.25, 0.18 and 0.13 μm) is compared. The variation of the noise parameter values is discussed with respect to the technology node. The highest oxide trap density is obtained for the thinnest gate oxide. It is concluded that the oxide thinning should lead to noise reduction only if the product t_ox². N_t is taken into consideration. This trend will be significant in future scaled-down MOSFETs.     

In0.48Ga0.52P/In0.20Ga0.80As/GaAs pseudomorphic high electron mobility transistors grown by solid-source molecular-beam epitaxy using a valved phosphorus cracker cell

In_0.48Ga_0.52P/In_0.20Ga_0.80As/GaAs pseudomorphic high electron mobility transistor (p-HEMT) structures were grown by solid-source molecular beam epitaxy (SSMBE) using a valved phosphorus cracker cell. The sheet carrier density at room temperature was 3.3 × 10¹²cm^?2. A peak transconductance (G _m) of 267 mS mm^?1 and peak drain current density (I _ds) of 360 mA mm^?1 were measured for a p-HEMT device with 1.25 µm gate length. A high gate-drain breakdown voltage (BV _gd) of 33V was measured. This value is more than doubled compared with that of a conventional Al_0.30Ga_0.70As/In_0.20Ga_0.80As/GaAs device. The drain-source breakdown voltage (BV _ds) was 12.5V. Devices with a mushroom gate of 0.25 µm gate length and 80 µm gate width achieved a peak transconductance (G _m) of 420 mS mm^?1 and drain current density of nearly 500mA mm^?1. A high cutoff frequency (f _T) of 58GHz and maximum oscillation frequency (f _max) of 120 GHz were obtained. The results showed that the In_0.48Ga_0.52P/In_0.20Ga_0.80As/GaAs material system grown by SSMBE using the valved phosphorus cracker cell for the In^0.48Ga^0.52P Schottky and spacer layers is a viable technology for high frequency p-HEMT device applications.     

A weak-to-strong inversion mismatch model for analog circuit design

This paper reports on a new CMOS transistor mismatch model that is continuous from weak to strong inversion. The model is completely described by analytical equations which are based on either the ACM or EKV transistor models. Large signal ACM and EKV transistor equations including the relevant parameters for mismatch are used for fitting the measured data. Five parameters are found to be relevant for predicting mismatch from weak to strong inversion: specific current I _s , threshold voltage V _T0, gamma γ, θ _o (dependent on mobility degradation and source-drain series resistances), and θ _e (dependent on velocity saturation and drain series resistance). Arrays of NMOS and PMOS transistors of 30 different sizes were fabricated in a 0.35 μm CMOS process. For each transistor size 12 different curves were measured. Different mismatch parameter extraction methods were used and compared. Average current mismatch prediction error was found to be in the range between 4 and 10% in the whole bias range from weak to strong inversion. Worst case mismatch prediction errors were in the range 23–61%. Since mismatch was predicted for a large number of sizes, the model could be implemented in a conventional circuit simulator to predict transistor mismatch not only as a function of transistor area but as function of transistor width and length independently. It was found that minimum mismatch is not always achieved by square transistors, and that mismatch is less sensitive to reducing width than to reducing length.     

Fully Transparent p‐MoTe2 2D Transistors Using Ultrathin MoOx/Pt Contact Media for Indium‐Tin‐Oxide Source/Drain

Since transition metal dichalcogenide (TMD) semiconductors are found as 2D van der Waals materials with a discrete energy bandgap, many 2D‐like thin field effect transistors (FETs) and PN diodes are reported as prototype electrical and optoelectronic devices. As a potential application of display electronics, transparent 2D FET devices are also reported recently. Such transparent 2D FETs are very few in report, yet no p‐type channel 2D‐like FETs are seen. Here, 2D‐like thin transparent p‐channel MoTe₂ FETs with oxygen (O₂) plasma‐induced MoO_x/Pt/indium‐tin‐oxide (ITO) contact are reported for the first time. For source/drain contact, 60 s short O₂ plasma and ultrathin Pt‐deposition processes on MoTe₂ surface are sequentially introduced before ITO thin film deposition and patterning. As a result, almost transparent 2D FETs are obtained with a decent mobility of ≈5 cm² V^?1 s^?1, a high ON/OFF current ratio of ≈10⁵, and 70% transmittance. In particular, for normal MoTe₂ FETs without ITO, O₂ plasma process greatly improves the hole injection efficiency and device mobility (≈60 cm² V^?1 s^?1), introducing ultrathin MoO_x between Pt source/drain and MoTe₂. As a final device application, a photovoltaic current modulator, where the transparent FET stably operates as gated by photovoltaic effects, is integrated.