Comparison of Valence-Band Tunneling in Pure SiO2, Composite SiO2 /Ta2O5, and Pure Ta2O5, in Mosfets with 1.0 nm-Thick SiO2-Equivalent Gate Dielectrics

1999 ◽  
Vol 567 ◽  
Author(s):  
A. Shanware ◽  
H. Z. Massoud ◽  
E. Vogel ◽  
K. Henson ◽  
J. R. Hauser ◽  
...  
Keyword(s):  
Valence Band ◽  
Gate Dielectric ◽  
Electron Tunneling ◽  
Tunneling Current ◽  
Dielectric Constants ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Gate Current ◽  
Gate Tunneling ◽  
Valence Bands

ABSTRACTThe gate tunneling current in ultrathin gate dielectric NMOSFETs with positive gate bias is due to the tunneling of electrons from the conduction and valence bands of the substrate. Valence-band electrons tunnel from the substrate of NMOS devices when the valence-band edge in the substrate rises above the conduction-band edge in the substrate. This paper reports experimental trends in the contribution of valence-band electrons tunneling to the gate current of NMOSFETs with gate oxides composed of pure SiO2. The large gate tunneling current can be reduced by replacing the conventional SiO2 gate dielectric with alternative dielectrics with larger dielectric constants. This paper reports the effect of replacing SiO2 with alternative dielectrics on the contribution of valence-band electron tunneling to the gate current. Simulations are carried out for composite SiO2/Ta2O5 gate dielectric structures.

scholarly journals Photocatalytic properties of a new Z-scheme system BaTiO3/In2S3 with a core–shell structure

RSC Advances ◽  
2019 ◽  
Vol 9 (20) ◽  
pp. 11377-11384 ◽  
Author(s):  
Kaili Wei ◽  
Baolai Wang ◽  
Jiamin Hu ◽  
Fuming Chen ◽  
Qing Hao ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Valence Band ◽  
Conduction Band ◽  
Shell Structure ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Core Shell ◽  
Valence Band Edge ◽  
Core Shell Structure ◽  
Positive Valence

It's highly desired to design an effective Z-scheme photocatalyst with excellent charge transfer and separation, a more negative conduction band edge (ECB) than O2/·O2− (−0.33 eV) and a more positive valence band edge (EVB) than ·OH/OH− (+2.27 eV).

scholarly journals Theoretical investigation on $$\hbox {BeN}_{{2}}$$ monolayer for an efficient bifunctional water splitting catalyst

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. R. Ashwin Kishore ◽  
R. Varunaa ◽  
Amirhossein Bayani ◽  
Karin Larsson
Keyword(s):  
Water Splitting ◽  
Valence Band ◽  
Conduction Band ◽  
Theoretical Investigation ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Substantial Impact ◽  
Solar Hydrogen Production

AbstractThe search for an active, stable, and abundant semiconductor-based bifunctional catalysts for solar hydrogen production will make a substantial impact on the sustainable development of the society that does not rely on fossil reserves. The photocatalytic water splitting mechanism on a $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer has here been investigated by using state-of-the-art density functional theory calculations. For all possible reaction intermediates, the calculated changes in Gibbs free energy showed that the oxygen evolution reaction will occur at, and above, the potential of 2.06 V (against the NHE) as all elementary steps are exergonic. In the case of the hydrogen evolution reaction, a potential of 0.52 V, or above, was required to make the reaction take place spontaneously. Interestingly, the calculated valence band edge and conduction band edge positions for a $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer are located at the potential of 2.60 V and 0.56 V, respectively. This indicates that the photo-generated holes in the valence band can oxidize water to oxygen, and the photo-generated electrons in the conduction band can spontaneously reduce water to hydrogen. Hence, the results from the present theoretical investigation show that the $$\hbox {BeN}_{{2}}$$ BeN 2 monolayer is an efficient bifunctional water-splitting catalyst, without the need for any co-catalyst.

A Compact Model for Valence-Band Electron Tunneling Current in Partially Depleted SOI MOSFETs

2007 ◽  
Vol 54 (2) ◽  
pp. 316-322 ◽  
Author(s):  
W. Wu ◽  
Xin Li ◽  
G. Gildenblat ◽  
G.O. Workman ◽  
S. Veeraraghavan ◽  
...  
Keyword(s):  
Valence Band ◽  
Electron Tunneling ◽  
Tunneling Current ◽  
Compact Model ◽  
Band Electron ◽  
Valence Band Electron

Electronic States in the Gap of a-Si from Bond Angle Variations

1990 ◽  
Vol 192 ◽  
Author(s):  
B. N. Davidson ◽  
G. Lucovsky
Keyword(s):  
Valence Band ◽  
Density Of States ◽  
Bond Angle ◽  
Bethe Lattice ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Valence Band Edge ◽  
Defect States ◽  
Discrete State ◽  
Bond Angles

ABSTRACTWe investigate the formation of defect states in the gap of a-Si arising from deviations from the ideal tetrahedral bond angles. The local density of states for Si atoms in disordered environments is calculated using tight-binding parameters for the cluster-Bethe lattice method. The Hamiltonian for a-Si with bond angle distortions is taken as an average over many configurations associated with a random choice of bond angles, weighted by Gaussian distributions with standard deviations between 2°.and 10°. Bond angle deviations in this range generate a density of defect states at the valence band edge that: 1) increases as the average bond angle deviation increases; and 2) is significantly larger than the density of band tail states generated at the conduction band edge. We obtain a shift of the absorption edge from the joint density of states (DOS) as a function of bond angle deviations. In addition, a calculation of the DOS for a distorted tetrahedral cluster embedded in an idealized Bethe lattice yields a threshold bond angle distortion of ±20° for the appearance of a discrete state in the gap near the valence band edge.

MODELING GATE CURRENT FOR NANO SCALE MOSFET WITH DIFFERENT GATE SPACER

2011 ◽  
Vol 20 (08) ◽  
pp. 1659-1675 ◽  
Author(s):  
ASHWANI K. RANA ◽  
NAROTTAM CHAND ◽  
VINOD KAPOOR
Keyword(s):  
Leakage Current ◽  
Scale Effects ◽  
Current Model ◽  
Tunneling Current ◽  
Oxide Semiconductor ◽  
Experimental Result ◽  
Gate Leakage ◽  
Gate Current ◽  
Nano Scale ◽  
Gate Tunneling

Dimensions of metal–oxide–semiconductor field effect transistor (MOSFET) have been scaled down for decades to maintain the performance. So, as a result of aggressive scaling, gate oxide thickness approaches its manufacturing and physically limiting value of less than 2 nm in nano regime. Under such circumstances, gate leakage (tunneling) current has become a critical problem in nano domain as compared to subthreshold leakage current. Consequently, accurate quantitative understanding of gate tunneling leakage current is very important especially in context of low power VLSI application. In this work, gate tunneling currents have been modeled including the inevitable nano scale effects for a MOSFET having different high-k dielectric spacer such as SiO2 , Si3N4 , Al2O3 , HfO2 . The gate current model is compared and contrasted with santaurus simulation results and reported experimental result to verify the accuracy of the model. The agreement found was good, thus validating the developed analytical model. It is observed that neglecting nano scale effects may lead to large error in the calculated gate current. It is found in the results that gate leakage current decreases with the increase of dielectric constant of the gate spacer. Further, it is also reported that the spacer materials impact the threshold voltage, on current, off current, drain induced barrier lowering, and subthreshold slope of the device.

Strain Modification of Band Edge Energies in a Pyramidal InAs-GaAs Quantum Dot System

2012 ◽  
Vol 501 ◽  
pp. 337-341 ◽  
Author(s):  
Gregory Henry Ripan ◽  
Geri Gopir ◽  
Ahmad Puaad Othman
Keyword(s):  
Monte Carlo ◽  
Quantum Dot ◽  
Valence Band ◽  
Interatomic Potential ◽  
Relaxation Method ◽  
Growth Direction ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Gaas Quantum Dot ◽  
Inas Quantum Dot

We present the calculated band edge energies altered by strain in a nanostructure system of a pyramidal InAs quantum dot buried in a GaAs substrate. Our zinc-blende supercell system of dimension 11.9 nm × 11.9 nm × 8.5 nm and 55119 atoms contains a pyramidal In770As886 quantum dot of 1656 atoms with height of 3.03 nm and square base of length 6.06 nm. The strain energy of this nanostructure system is minimized by employing the Keating formulation of interatomic potential and Monte Carlo relaxation method via the Metropolis algorithm. This relaxation is run for 20 million Monte Carlo steps at simulation temperature of 4.2 K. The calculated strain is then used to determine the conduction and valence band edge energies of the nanostructure. We find that along the [001] growth direction in the InAs quantum dot region, strain increases the conduction band edge energy by 0.6 eV and in the valence band strain results in relatively sharp wells at the dot base for heavy holes and at the dot tip for light holes. Thus, our calculation predicts that strain leads to increased band gap and spatial splitting of holes in this nanostructure system.

First principles study of electronic structures of dopants in Mg2Si

2011 ◽  
Vol 1329 ◽  
Author(s):  
K. Xiong ◽  
S. Sobhani ◽  
R. P. Gupta ◽  
W. Wang ◽  
B. E. Gnade ◽  
...  
Keyword(s):  
Band Gap ◽  
Valence Band ◽  
Conduction Band ◽  
Density Of States ◽  
First Principles ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Hybrid Functional ◽  
Thermoelectric Efficiency ◽  
The Impact

ABSTRACTWe investigate the impact of various dopants (Na, Ag, Cd, Zn, Al, Ga, In, Tl, Ge, and Sn) on the electronic structure of Mg2Si by first principles calculations using a hybrid functional that does not need a band gap correction. We find that for Na and Ge in Mg2Si, the impurity-induced states do not affect the density of states at both edges of the valence band and the conduction band. Ag- and Sn affect slightly the density of states at the valence band edge, while Cd and Zn affect slightly the density of state at the conduction band edge. Al and In could modify significantly the density of states at the conduction band edge. Ga introduces states just at the bottom of the conduction band. Tl introduces states in the band gap. This study provides useful information on optimizing the thermoelectric efficiency of Mg2Si.

Modeling the Dependence of the Gate Current on Ge Content in Ultrathin Gate Dielectric Pmos Devices with Poly-Si1−Gex Gate Material

1999 ◽  
Vol 567 ◽  
Author(s):  
A. Shanware ◽  
H. Z. Massoud ◽  
A. Acker ◽  
V. Z. Q. Li ◽  
M. R. Mirabedini ◽  
...  
Keyword(s):  
Energy Level ◽  
Valence Band ◽  
Gate Dielectric ◽  
Gate Dielectrics ◽  
Tunneling Current ◽  
Current Drive ◽  
Future Generations ◽  
Band Energy ◽  
Flatband Voltage ◽  
Valence Band Energy

ABSTRACTThe performance of CMOS devices improves due to the addition of Ge in their poly-Si gate material. The presence of Ge in the gate increases the current drive due to the reduction of the flatband voltage. The change in the flatband voltage is due to a shift in the valence-band energy level in the gate. This shift results in a change in the barrier height for electrons tunneling from the gate. Thus, the presence of Ge in the gate increases the tunneling current in the gate. This increase may result in a limitation in the use of SiGe gates in future generations of MOSFETs with ultrathin gate dielectrics. The purpose of this work is to investigate the effect of Ge content on the tunneling current in CMOS devices with ultrathin gate dielectrics.

The Distribution of Occupied Deep Levels in a-Si:H Determined from CPM Spectra

1991 ◽  
Vol 219 ◽  
Author(s):  
Nobuhiro Hata ◽  
Sigurd Wagner
Keyword(s):  
Valence Band ◽  
Conduction Band ◽  
Peak Height ◽  
Peak Position ◽  
Deep Levels ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Defect States ◽  
Model Calculations ◽  
Annealed State

ABSTRACTWe report the determination of the distribution of occupied defect states in hydrogenated amorphous silicon from the deconvolution of constant photocurrent measurement (CPM) spectra, and the modelling of the distribution with the defect pool.The CPM spectra were taken on undoped a-Si:H samples either in their as-grown state, in the annealed state, after quenching from high temperature, or after light-soaking. The spectra were deconvoluted to account for transitions from deep levels and from valence band tail states to a conduction band assumed to have a sharp edge. As-grown or annealed-state samples show a peak at 1.0 eV (0.2 eV FWHM) below the conduction band edge. Assuming a mobility gap of 1.9 eV, this peak lies 0.9 eV above the valence band edge. We ascribe this peak to the Do/+ transition. CPM spectra of light-soaked and thermally quenched samples show shifts in the peak position and increases in die peak height in accordance with the defect pool model. The model calculations agree with the CPM results, so that the applicability of CPM spectral analysis to obtaining detailed values of defect pool parameters is demonstrated.

scholarly journals The band-edge excitons observed in few-layer NiPS3

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Ching-Hwa Ho ◽  
Tien-Yao Hsu ◽  
Luthviyah Choirotul Muhimmah
Keyword(s):  
Valence Band ◽  
Conduction Band ◽  
Lower Energy ◽  
Transition Energy ◽  
Threshold Energy ◽  
Band Edge ◽  
Conduction Band Edge ◽  
Rydberg Series ◽  
Optical Gap ◽  
Energy Side

AbstractBand-edge excitons of few-layer nickel phosphorous trisulfide (NiPS3) are characterized via micro-thermal-modulated reflectance (μTR) measurements from 10 to 300 K. Prominent μTR features of the A exciton series and B are simultaneously detected near the band edge of NiPS3. The A exciton series contains two sharp A1 and A2 levels and one threshold-energy-related transition (direct gap, E∞), which are simultaneously detected at the lower energy side of NiPS3. In addition, one broadened B feature is present at the higher energy side of few-layer NiPS3. The A series excitons may correlate with majorly d-to-d transition in the Rydberg series with threshold energy of E∞ ≅ 1.511 eV at 10 K. The binding energy of A1 is about 36 meV, and the transition energy is A1 ≅ 1.366 eV at 300 K. The transition energy of B measured by μTR is about 1.894 eV at 10 K. The excitonic series A may directly transit from the top of valence band to the conduction band of NiPS3, while the B feature might originate from the spin-split-off valence band to the conduction band edge. The direct optical gap of NiPS3 is ~1.402 eV at 300 K, which is confirmed by μTR and transmittance experiments.

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