<div>We derive an analytical model for 1/f noise in MOSFETs, highlighting a term that is often neglected in literature but becomes important for ultra-thin oxides. Furthermore, we identify an interesting relationship between the thermal noise of the gate impedance and the gate noise due to trapping/detrapping between the free carriers in the channel and the oxide traps, as well as the 1/f noise cross-correlation between drain and gate, showing that a single voltage noise generator is not enough to describe completely the 1/f noise. TCAD simulations are used to verify the model predictive capabilities.</div>
In this work, we describe how the frequency dependence of conductance (G) and capacitance (C) of a generic MOS capacitor results in peaks of the functions G/ω and - ωdC/dω. By means of TCAD simulations, we show that G/ω and -ωdC/dω peak at the same value and at the same frequency for every bias point from accumulation to inversion. We illustrate how the properties of the peaks change with the semiconductor doping (N D ), oxide capacitance (C OX ), minority carrier lifetime (τ g ), interface defect parameters (N IT , σ) and majority carrier dielectric relaxation time (τ r ). Finally, we demonstrate how these insights on G/ω and -ωdC/dω can be used to extract CO X , N D and τ g from InGaAs MOSCAP measurements.
In this work we employ a state-of-the-art Multi-Subband Monte Carlo simulator to investigate the performance of III-V n-MOSFETs with L G = 11.7nm. We analyze GaSb versus InGaAs strained and unstrained channel materials and the implications of Fermi level pinning on electrostatic and transport. We found that InGaAs MOSFETs can outperform strained silicon for low V DD applications. Advantages related to strained InGaAs are limited and mainly due to reduced Fermi Level Pinning.
A theory of stimulated Brillouin scattering (SBS) has been developed for metallic nanohybrid fiber, which is made of an ensemble of metallic nanoparticles doped in a dielectric nanofiber. We consider that input probe light photons scatter within the nanohybrid and produce stimulated Brillouin scattered photons and acoustic phonons. The coupled-mode formalism based on Maxwell’s equations is used to obtain the SBS intensity, the SBS energy, and the SBS absorption coefficient. It is found that the SBS depends on the third-order susceptibility, which is evaluated by the density matrix method. An analytical expression of the SBS intensity, energy, and absorption coefficient is calculated in the presence of surface plasmon polaritons (SPPs) and dipole-dipole interactions (DDI) between nanoparticles in the ensemble. Next, we have compared our theory with the experimental data for a nanohybrid made of an ensemble of Au-nanorods doped in water. A good agreement between theory and experiment is found. We have also performed the numerical simulations to study the effect of SPP and DDI fields on the SBS intensity. We have predicted an enhancement in the SBS intensity due to the SPP and DDI couplings. The enhancement is due to not only the scattering mechanisms of the probe photons with acoustic phonons but also the extra scattering mechanisms from the SPP and DDI polaritons with acoustic phonons. The SBS analytical expressions can be useful for experimental scientists and engineers who can use them to plan new experiments and make new types of plasmonic devices. The enhancement effect can be used to fabricate new types of SBS nanosensors and amplifiers.
The advent of two-dimensional materials has opened a plethora of opportunities in accessing ultrascaled device dimensions for future logic and memory applications. In this work, we demonstrate that a single layer of large-area chemical vapor deposition-grown molybdenum disulfide (MoS2) sandwiched between two metal electrodes can be tuned to show multilevel nonvolatile resistive memory states with resistance values separated by 5 orders of magnitude. The switching process is unipolar and thermochemically driven requiring significant Joule heating in the reset process. Temperature-dependent electrical measurements coupled with semiclassical charge transport models suggest that the transport in these devices varies significantly in the initial (pristine) state, high resistance state, and low resistance state. In the initial state, the transport is a one-step direct tunneling (at low voltage biases) and Fowler Nordeim tunneling (at higher bias) with an effective barrier height of 0.33 eV, which closely matches the Schottky barrier at the MoS2/Au interface. In the high resistive state, trap-assisted tunneling provides a reasonable fit to experimental data for a trap height of 0.82 eV. Density functional theory calculations suggest the possibility of single- and double-sulfur vacancies as the microscopic origins of these trap sites. The temperature-dependent behavior of the set and reset process are explained by invoking the probability of defect (sulfur vacancy) creation and mobility of sulfur ions. Finally, conductive atomic force microscopy measurements confirm that the multifilamentary resistive memory effects are inherent to a single-crystalline MoS2 triangle and not necessarily dependent on grain boundaries. The insights suggested in this work are envisioned to open up possibilities for ultrascaled, multistate, resistive memories for next-generation digital memory and neuromorphic applications.
We review the Monte Carlo method to model semi-classical carrier transport in advanced semiconductor devices. We report examples of the use of the Multi-Subband Monte Carlo method to simulate MOSFETs with III-V compound semiconductor channel. Monte Carlo transport modeling of graphene-based transistors is also addressed.
Impedance spectroscopy of the metal-oxide semiconductor (MOS) system has played a central role in the development of silicon-based complementary MOS (CMOS) technology over the past 50 years [1, 2]. With current research interest into alternative semiconductor channels to silicon for MOSFET and tunnel FET technologies, the measurement and interpretation of the overall impedance of the MOS structure requires detailed analysis to separate and quantify the contribution of interface states, and near interface traps (border traps), on the capacitance and conductance response, and to separate the contribution of these electrically active defect states from the ac response of minority carriers in the case of genuine inversion of the semiconductor/dielectric interface. There has been considerable progress in recent years in reducing the interface state density (D it ) [3], [4], [5], in narrow gap In x Ga 1-x As MOS structures to the point where genuine surface inversion can be observed for both n- and p-type In 0.53 Ga 0.47 As MOS capacitors, which is confirmed by analysis of the minimum capacitance of n- and p-type In 0.53 Ga 0.47 As MOS structure with doping concentration ranging from approximately 1x10 16 to 1x10 18 cm -3 [6]. In this presentation we will provide an overview of the experimental relationship between specific functions of the capacitance (C) and conductance (G) for the case of narrow band gap III-V MOS structures which exhibit genuine surface inversion, where the capacitance and conductance of the MOS system as a function of ac angular frequency (ω) are related, and in particular, the peak values of G/ω and −dC/dlog e (ω) (≡− ωdC/dω) are equal, and that these peak magnitudes occur at the same value of ω [7]. The relationship is also confirmed by physics based ac simulations of MOS structures and through analysis of the equivalent circuit model in inversion. Results will be presented for InGaAs and InGaSb MOS structures (Al 2 O 3 and Al 2 O 3 /HfO 2 ALD oxides) where genuine inversion of the III-V/oxide surface is confirmed by the G/ω and −dC/dlog e (ω) functions, which have peak values of C ox 2 /2(C ox +C d ) when the surface is inverted (where C ox is the gate oxide capacitance and C d is the maximum capacitance of the semiconductor surface in inversion). In the case of p type InGaSb MOS structures it is also notable that the accumulation frequency dispersion is very low (<0.7%/decade) indicating a reduced density of border traps at energies in the Al 2 O 3 gate oxide aligning with the In 0.3 Ga 0.7 Sb valence band edge, which is approximately aligned with the lowest energy in the In 0.53 Ga 0.47 As conduction band gamma valley. Finally, experimental results and physics based simulations will be presented, which indicate that the peak values of G/ω and −dC/dlog e (ω) in inversion for any MOS system which demonstrates an inversion response within the typically range of temperatures and ac signal frequencies employed in experiments, opens a route to determine the gate oxide capacitance in inversion (where the gate oxide field and gate leakage are reduced), and that the angular frequency associated with the peak values of the G/ω and −dC/dlog e (ω) functions allows the determination of the minority carrier generation rate in the semiconductor, which is relevant to the leakage currents in MOSFETs and the optical performance in photonic applications. [1] E. H. Nicollian and J. R. Brews, MOS Physics and Technology. New York, NY, USA: Wiley, 1982 [2] E. H. Nicollian and A. Goetzberger, “The Si-SiO2 interface—Electrical properties as determined by the metal-insulator-silicon conductance technique,” Bell Syst. Tech. J., vol. 46, no. 6, pp. 1055–1133, 1967. [3] É. O’Connor et al., J. Appl. Phys., vol. 109, no. 2, p. 024101, 2011. [4] H.-D. Trinh et al., Appl. Phys. Lett., vol. 97, no. 4, pp. 042903-1–042903-3, 2010. [5] T. D. Lin et al., “Realization of high-quality HfO2 on In0.53Ga0.47As by in-situ atomic-layer-deposition,” Appl. Phys. Lett., vol. 100, no. 17, p. 172110, 2012. [6] E. O'Connor, K. Cherkaoui, S. Monaghan, B. Sheehan, I. M. Povey, and P. K. Hurley, Appl. Phys. Lett 110, 032902 (2017) [7] Scott Monaghan, Éamon O’Connor, Rafael Rios, Fahmida Ferdousi, Liam Floyd, Eimear Ryan, Karim Cherkaoui, Ian M. Povey, Kelin J. Kuhn, and Paul K. Hurley, IEEE Transaction on Electron Devices, 61, 4176 (2014)
A comprehensive description of band gap and effective masses of III–V semiconductor bulk and ultra-thin body (UTB) structures under realistic biaxial and uniaxial strain is given using numerical simulations from four different electronic structure codes. The consistency between the different tools is discussed in depth. The nearest neighbor sp 3 d 5 s* empirical tight-binding model is found to reproduce most trends obtained by ab initio Density Functional Theory calculations at much lower computational cost. This model is then used to investigate the impact of strain on the ON-state performance of realistic In 0.53 Ga 0.47 As UTB MOSFETs coupled with an efficient method based on the well-known top-of-the-barrier model. While the relative variation of effective masses between unstrained and strained cases seems promising at first, the calculations predict no more than 2% performance improvement on drive currents from any of the studied strain configurations.