Gaussian Trap Distribution Research Articles

Discrete trapping levels of localized states in amorphous silicon nitride

The spectrum of localized hole states (traps) in amorphous silicon nitride, a-Si3N4, is experimentally studied using the method of thermally stimulated depolarization. The experiment is compared with theoretical calculations using three models of the energy spectrum of traps: discrete spectrum (monoenergetic trap), continuous spectrum, and Gaussian trap distribution. The experiment is quantitatively described by a model of a discrete spectrum of traps with an energy of 1.15 eV and a width of no more than 0.01 eV. In the case of a continuous and Gaussian spectrum of traps, the contribution to depolarization is made by the deepest traps. The blurring of the trap energy level in a-Si3N4 due to the absence of long-range order (fluctuations in the Si–N bond length and fluctuations in the N–Si–N and Si–N–Si angles) does not exceed 0.01 eV.

Noise analysis of NC-GAAFET cylindrical nanowire with non-uniform interface trap charge

In this article, low to high frequency noise behavior analysis of negative capacitance gate-all-around field effect transistor (NC-GAAFET) MFIS structure Silicon Nanowire (SiNW) device, using Sentauras TCAD simulations, is investigated. The NC-GAAFET SiNW yields on current (ION) 5.31 times larger and off current (IOFF) is significantly reduced by ∼ 105 orders compared to baseline SiNW. The device exhibits an excellent switching ratio of 5.2 × 1014. Average subthreshold swing for the NC-GAAFET is 33 mV/dec compared to 64 mV/dec of baseline nanowire. The Negative-DIBL for the device is −20 mV/V which outshines earlier findings. Furthermore, the drain current noise power spectral density (PSD) Sid, and input referred gate voltage noise PSD (Svg) are comprehensively analyzed in the presence of Gaussian trap (non-uniform) distribution. The analysis indicates that, flicker or (1/f) noise dominates in low frequency regime, generation-recombination (G-R) noise is more influential in mid frequency regime whereas in very high frequency regime diffusion noise is leading. The device exhibits least Sid(NET) and Svg(NET) at tfe = 6 nm compared to baseline, tfe = 5 nm, and 7 nm.

Study on trap sensitivity for single material gate and double material gate nano-ribbon FETs

In this work, the trap sensitivity of single material gate (SMG) and dual material gate (DMG) nano ribbon FETs (NRFETs) are reported using TCAD Sentaurus Device simulator. The trap sensitivity is extracted for Gaussian trap distribution of both acceptor and donor type traps. We have reported the trap sensitivity for the variation in trap concentration, energy peak position, work function of metal gate, and temperature for both the NRFETs. It is realized that trap sensitivity is greater and lesser than 100% for acceptor type trap in SMG and DMG NRFETs, respectively, whereas, such sensitivity is 147% and 123% for donor type trap concentration, respectively. Temperature also shows a significant variation in trap sensitivity for both the NRFETs. The increase in work function leads to the reduction in trap sensitivity for both NRFETs in existence of acceptor and donor trap charges. The maximum sensitivity in trap are 400% and 275% for SMG and DMG NRFETs, respectively, in presence of donor trap concentration. Moreover, the trap sensitivity is very insignificant at high gate bias for donor type trap concentration with wide variation in parameters.

Physical insights of interface traps and self-heating effect on electrical response of DMG FinFETs in overlap and underlap configurations: analog/RF perspective

This paper presents a thorough analysis on analog/RF parameters including interface trap charges (ITCs) of two different densities of states (DOS) along with self-heating on the performance of DMG FinFETs in Overlap and Underlap configurations. Initially, the independent simulations for acceptor ITCs and Self-heating in conventional device reveals that performance degradation caused by Self-heating is more prominent (25.03%) than uniform acceptor ITCs (9.46%). In consecutive step, the cumulative impact of both acceptor ITCs and Self-heating on DC and RF/analog parameters are carried out. Investigation reveals that as the impact of self-heating is larger in overlap configuration, the degradation in drain current is higher in overlap configuration (45.2%, 54.5%) as compared to conventional (30.4%, 40.96%) and underlap (37.2%, 52.8%) configurations for both Uniform and Gaussian trap distributions, respectively.

Investigation of the Temperature Dependence of Volt-Ampere Characteristics of a Thin-Film Si3N4 Memristor

The compatibility of memristor materials with advanced complementary metal-oxide-semiconductor (CMOS) technology is a key factor for microelectronics element base manufacturing. Therefore, we continued studying previously fabricated CMOS-compatible Ni/Si3N4/SiO2/p+-Si samples. We approximated volt-ampere characteristics (VAC) at different temperatures using the general form of the spatial charge-limiting current (SCLC) equation assuming exponential and Gaussian trap distribution within the band gap of Si3N4. Our approximation demonstrated better experimental data matching compared to previous work, where the approximation was based on the uniform trap distribution law. Further, we performed another additional sample measurement set of the samples to evaluate the parameters of the low-resistance state (LRS) variations at different temperatures. Analysis of these measurements allowed us to estimate the temperatures at which the samples will retain LRS for 10 years.

Electrical Noise Analysis of Z Shape Horizontal Pocket and Hetero Stack TFETs under Trap Distribution

In this work, a comprehensive investigation on noise analysis for two different low power devices, namely Z-shaped Horizontal Pocket (ZHP) and Hetero Stack (HS) TFETs, is presented within low to high frequency range. The simulation is performed for these structures in the presence of Uniform and Gaussian trap distributions at the interface of Silicon and oxide materials for three different noise namely Flicker noise, Generation Recombination (GR) noise, and Diffusion noise with the help of the Sentaurus TCAD simulator. The result reveals that Flicker and GR noise are dominates at Low Frequency, while, the diffusion noise reports significant influence at the high-frequency range. Finally, a comparative analysis has been done in terms of noise current spectral density (Sid) of the considered structures with the existing literature.

Low to high-frequency noise behavior investigation of steeper sub-threshold swing NC-GeFinFET

The role of noise effect, in presence of Gaussian-trap distribution on the negative capacitance germanium FinFET (NC-GeFinFET) by using Sentaurus-TCAD is investigated. Incorporation of ferroelectric FE-layer in NC-GeFinFET, ION boosts by almost 18% compared to the baseline FinFET. Also steeper sub-threshold swing (SS) of 7.4 mV/decade is achieved by using the FE-layer of thickness (tfe) 6 nm at the room temperature. Result reports how the 1f noise and Generation-Recombination (G-R) noise plays an important role in net drain current spectral density (net Sid) for the proposed device up to mid frequency range, and the diffusion noise dominates in the high frequency range. This study highlights the analysis of net Sid with respect to frequency for different tfe. The minimum net Sid value 4.45 ×10−16 A2/Hz is achieved at 10 Hz, in presence of Gaussian-trap, for tfe 6 nm and is compared with the results for tfe 4 nm and 5 nm. This shows the importance of FE-layer in achieving low net Sid, especially in high frequency regime.

Investigation of Step Fin (SF), Step Drain (SD) and Step Source (SS) FinFETs with Trap Effect

In this paper, the RF and analog performances of the triple material gate (TMG) step Fin (SF) FinFET, step drain (SD) FinFET, and step source (SS) FinFET have been explored by 3D TCAD simulation. We have simulated the performance in the presence of uniform trap (UT) and Gaussian trap (GT) distribution with a fixed value of trap concentration (1012 eV−2cm−2). The various DC parameters, such as threshold voltage (Vth), sub-threshold swing (SS), and switching ratio, are observed in trap distribution. The outcome of this simulation study is that the SF FinFET structure has shown 25.1% and 33.95% enhancement of drive current compared to SD FinFET and SS FinFET, respectively. On the other hand, SS FinFET has shown an enhancement of 1.2x(9.8x) on gain transconductance frequency product (GTFP), 1.21x(1.01x) of transconductance frequency product (TFP), 4.19x(23.28x) of intrinsic gain (Av), 1.88x(21.21x) of gain frequency product (GFP), and 4.18x(9.69x) of the gain-bandwidth product (GBP) compared to SD FinFET (SF FinFET).

Generation-recombination in disordered organic semiconductor: Application to the characterization of traps

The presence of traps in organic semiconductor based electronic devices affects considerably their performances and their stability. The Shockley-Read-Hall (SRH) model is generally used to extract the trap parameters from the experimental results. In this paper, we propose to adapt the SRH formalism to disordered organic semiconductors by considering a hopping transport process and Gaussian distributions for both mobile and trapped carriers. The model is used to extract multiple trap parameters from charge based Deep Level Transient Spectroscopy (Q-DLTS) spectrum. Calculation of the charge transients are given in detail. The model predicts that the activation energy of the trap should not follow an Arrhenius plot on large temperature ranges. Also, the charge transients are no longer exponential when considering Gaussian trap distributions, enlarging the Q-DLTS peaks. The model fits the Q-DLTS spectra measured on organic diodes with a limited number of trap contributions with a good agreement. It is found that an increase of the material rate of disorder reduces the extracted trap energy distances to the LUMO but has no influence on the extracted trap distribution widths. This work shows the importance of considering the specific properties of organic materials to study their properties and their trap distributions. • A trap emission model has been developed for OSCs including hopping transport and Gaussian DOS for free carriers and traps. • Model predictions: the OSC disorder, i.e., to the width of the intrinsic Gaussian DOS, strongly influences the determined trap energies. • The emission model is validated by extracting trap parameters in organic diodes from Q-DLTS measurements.

Simulation of two-transistor parallel and series circuits for gas sensing validated by experimental data

Organic field effect transistors (OFETs) in parallel and series circuit configurations are simulated and tested for gas sensing activity. The devices are based on PQT12 and PQTS12 organic semiconductor thin films. A two-dimensional finite element simulation methodology is implemented. It is assumed that traps due to defects and grain boundaries are uniformly distributed throughout the semiconductor film. Gaussian trap distributions are used in the simulation. Gas sensing is accounted for by a doping-dependent hopping mobility model in the organic active material. Interface traps and charges at the interface between the polymer channel and gate insulator are incorporated. Transistors in both parallel and series configurations are studied. Compared to individual OFET-based sensors, the circuit configuration achieves significantly increased sensitivity to analyte, as indicated by the simulation and in agreement with experimental observations. This supports the concept of combining transistors to enhance analyte sensitivity and provides a method for advance screening of combinations of OFETs for high signal-to-drift ratios. The absolute value of drain currents for series circuits is lower than that of parallel circuits; however, the series circuits display higher analyte sensitivity.

The impact of donor/acceptor types of interface traps on selective buried oxide TFET characteristics

This paper investigates the reliability of the selective buried oxide TFET δp+ silicon-germanium layer at the tunneling junction. The impact of various uniform and Gaussian trap distributions and energies on the band-to-band tunneling current has been examined. The device has been optimized for different gap positions in the buried oxide. The OFF current of the proposed device is 1.7 × 10−18 A/µm. It has been observed that the effect of Gaussian trap is more compared to that of uniform trap. The study quantifies the DC parameters such as ION/IOFF ratio, subthreshold swing against different types of interface traps (donor or acceptor), density (Dit), position (near the tunneling junction or oxide/channel interface) and trap energy level (Etrap). Drain current reduces in the presence of acceptor-type trap and the variation is more for large trap density (1 × 1014 cm−3). An opposite behavior is perceived in the presence of donor-type traps. The device with highest acceptor trap concentration (1 × 1014 cm−3) provides minimum ON current of 2.21 × 10−6 A/µm whereas in case of donor trap concentration (1 × 1014 cm−3), highest ON current of 2.93 × 10−5 A/µm is obtained. The device with no traps proves to be better by providing maximum ION/IOFF ratio of 3.89 × 1012 with SS of 45 mV/dec. Further, the affectability of quantum correction on various electrical parameters has been studied for different types of traps.

An insight to the performance of vertical super-thin body (VSTB) FET in presence of interface traps and corresponding noise and RF characteristics

We investigated vertical super-thin body (VSTB) FET performance in presence of different interface (HfO2/Si) trap distributions (uniform and Gaussian) and concentrations using TCAD tools. For trap concentration (TC) of 1013 eV−1 cm−2, the percentage change in on-to-off current ratio (Ion/Ioff) is 93.91% for uniform trap (UT) and 49.8% for Gaussian trap (GT) distribution. For the same TC, subthreshold swing (SS) shows percentage change of 5.1% for UT and 11.41% for GT distribution. Thus, the device performance shows good immunity for TC up to 1013 eV−1 cm−2. However, for TC = 1014 eV−1 cm−2 SS degrades significantly. The influence of traps on the cumulative effect of three noise sources (diffusion + generation–recombination/G–R + flicker) and on individual noise sources (G–R and diffusion) is explained qualitatively at low and high frequencies (f = 1 MHz and 10 GHz). The study shows that the overall noise cannot disturb the device performance at very high frequency. Various radio-frequency (RF) parameters like transconductance (gm), total input capacitance (Cgg), gate-drain capacitance (Cgd), unit-gain cutoff frequency (fT), and gain–bandwidth-product (GBP) are also studied for variation of trap types. For TC = 1014 eV−1 cm−2, the percentage change in fTmax (GBPmax) is − 21.43% (− 8%) for UT and − 22.86% (− 9.6%) for GT distribution.

Theoretical study of time-resolved luminescence in semiconductors. III. Trap states in the band gap

In the third part of this series, we study the influence of trap states in the band gap of semiconductors on the time-resolved luminescence decay (TRL) after a pulsed excitation. The results based on simulations with Synopsys TCAD® and analytical approximations are given for p-doped Cu(In,Ga)Se2 as a working example. We show that a single trap can be mostly described by two parameters which are assigned to minority carrier capture and emission. We analyze their influence on the luminescence decay and study the difference between a single trap and an energetic Gaussian trap distribution. It is found that trap states artificially increase the TRL decay and obscure the recombination dynamics. Thus, there is a demand for experimental methods which can reveal the recombination of minority carriers in a TRL experiment without trapping effect. In this regard, a variation of the device temperature, the excitation frequency, the injection level, as well as a bias illumination may be promising approaches. We study these methods, discuss advantages and disadvantages, and show experimental TRL for prove of concept. At the end, we validate our approach of simulating only band-to-band radiative recombination although photoluminescence spectra often exhibit free-to-bound radiative recombination of charge carriers.

Electrical noise in Circular Gate Tunnel FET in presence of interface traps

This paper presents a novel architecture of Tunnel Field Effect Transistor (TFET) with a circular gate and reports the effect of electrical noise on the device by comparing the results with a hetero-junction TFET. TCAD simulations involving uniform and Gaussian trap distribution conclude that the proposed Circular Gate TFET shows lesser values of noise spectral density than hetero-junction TFET. At lower frequencies, both generation–recombination noise and flicker noise dominate; at mid frequencies, only flicker noise contributes and at higher frequencies, diffusion noise dominates. Drain current in Circular Gate TFET is more prone to traps than Hetero-Junction TFET. The use of gate–drain underlap enhances the cut-off frequency of the CG-TFET in presence of Gaussian traps and makes it suitable for digital applications.

Hole Transport in Bisphenol-A Polycarbonate Doped with N,N′-Diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine

The time-of-flight (TOF) transients of solution-cast, free-standing films of N,N′-diphenyl-N,N-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′diamine (TPD) in bisphenol A polycarbonate (PC) have been studied using electron gun induced charge generation. This molecularly doped polymer (MDP) has been shown to exhibit perfectly flat plateaus on its time-of-flight curves with optical excitation. Our TOF results with continuously changing electron energies, as well as numerical calculations using a multiple trapping model with a Gaussian trap distribution (MTMg), suggest that charge carrier transport in this molecularly doped polymer is nonequilibrium and the flat plateaus can be explained by the presence of a thin surface layer depleted of transport material. The depleted surface layers on samples of this molecularly doped polymer are extremely thin (less than 0.12 μm), with those relating to the release side (contacting a substrate during coating/drying procedure) being much smaller than for the free side exposed t...

The temperature dependence and field dependence of the mobility of charge carriers in the multiple-trapping model with a Gaussian trap distribution

The multiple-trapping model with a Gaussian trap distribution was used for the numerical analysis of the effects of nonequilibrium transport on the temperature dependence and field dependence of the mobility of carriers in a typical molecularly doped polymer. It was shown that, with allowance for the prescribed Poole-Frenkel-type field dependence of mobility under the conditions of nonequilibrium transport, the observed decrease in the effective energy of disorder may be explained as a compensation effect with no change in the initial energy distribution of hopping centers.

Retention characteristics of gate-all-around metal–oxide–nitride–oxide–semiconductor devices for the trap energy level dependence at elevated temperature

We present an investigation of the retention characteristics of three-dimensional (3D) gate-all-around metal–oxide–nitride–oxide–semiconductor (GAA-MONOS) devices. The effect of retention charge loss in 3D GAA-MONOS devices at elevated temperatures has been experimented and studied by technology computer-aided design (TCAD) simulation. In particular, we considered the dependence of the trap energy level in the silicon nitride layer on the retention characteristics of the 3D GAA-MONOS devices by TCAD simulation. Here, simulation results showed that acceptor trap energy level considerably affects the retention charge loss compared with donor trap energy level in the silicon nitride layer that has a Gaussian trap distribution. Moreover, as the acceptor trap energy level becomes shallower, the effect on retention charge loss increases with increasing temperature. From these results, we confirmed that the simulation results for the retention characteristics of 3D GAA-MONOS devices were in reasonable agreement with the experimental results.

Charge carriers' trapping states in pentacene films studied by modulated photocurrent

The modulated photocurrent (MPC) technique is employed to study the charge carriers' trapping states of pentacene films. The characteristics of the experimental MPC spectra were found to be compatible with trapping-detrapping process of holes in gap states in which their occupancy can be modified by the bias illumination. A demarcation energy level separating empty from partially occupied traps was deduced from the MPC spectra, which can be used to monitor bias-light induced changes in the quasi Fermi level. An exponential trap distribution from structural disorder and a deep metastable gaussian trap distribution from adsorbed environmental impurities were extracted by means of the MPC spectroscopy. An attempt to escape frequency of the order of 1010s−1 was deduced for the gap sates. The derived trap distributions agree with those found before by means of other techniques. The present results indicate that the MPC technique can be used as a valuable tool for pentacene films characterization since it can be also applied to field effect samples.

Bimolecular recombination in molecularly doped polymers

We have investigated the bimolecular recombination of holes and electrons in a typical hole-conducting molecularly doped polymer (DEH-doped polycarbonate). The method used is a variant of the time-of-flight technique with the bulk generation of charge carriers. A small signal regime has been used to extract parameters of the multiple trapping model with an exponential as well as the Gaussian trap distributions. Then, using a large signal regime with the generation rate increasing sequentially in a power of 10, we compared model predictions with experiment. It was found that the best agreement is achieved once the Langevin recombination coefficient is used, this being defined by the microscopic mobility featuring in the models. The relevance of this fact to the published data has been addressed as well.

Analysis of the carrier transport in molecularly doped polymers using the multiple trapping model with the Gaussian trap distribution

We have performed the comprehensive analysis of the time of flight curves using the multiple trapping model with the Gaussian trap distribution. Our analysis shows that flat plateaus on the computed curves are rare events. We have shown numerically that plateau formation for the non-equilibrium transport may be due to the presence of a thin defective (depletion) layer on the sample surface (two-layer model of a polymer film). Also, to describe the Poole–Frenkel effect, we have explicitly introduced an analogous field dependence for the frequency factor.