Change In Energy Band Gap Research Articles

Effect of uniaxial strain on electrical properties of CNT-based junctionless field-effect transistor: Numerical study

Numerical studies on junctionless carbon nanotube field-effect transistors (JL-CNTFETs) have indicated that these devices produce more ON current than silicon junctionless transistors in comparable dimensions. Nevertheless, due to the smaller bandgap and quantum confinement effects, they provide weaker results in the OFF state. Since the change of energy bandgap is one of the effects of applying uniaxial strain on CNTs, in this paper, using non-equilibrium Green's function method (NEGF), the effects of applying strain on electrical characteristics of JL-CNTFETs, such as ION and IOFF, intrinsic delay, ION/IOFF ratio, power-delay product, unity-gain frequency, gate transconductance, and output resistance are investigated. The simulation results show that uniaxial stain, significantly alters the OFF state behavior and as a result the electrical properties of the device.

Intrinsic defects and structural phase of ZnS nanocrystalline thin films: effects of substrate temperature

Fabrications of ZnS nanocrystalline thin films at different substrate temperatures (TS) of 200, 300 and 400 °C by means of pulsed laser deposition are presented. Thin film deposited at TS of 200 °C is in cubic zinc-blende (ZB) structure while those deposited at TS of 300 and 400 °C are in hexagonal wurtzite (W) phase. The grain size, surface roughness and bandgap of the films increases with increasing TS. The zinc vacancies and interstitials in the films increases while sulfur vacancies decreases with increasing TS. The variation of zinc and sulfur vacancies in ZnS films with TS is responsible for structural phase transition from ZB to W which causes the change in energy bandgap.

Structural, chemical and electrical properties of ALD‐grown HfxAl1–xOy thin films for MIM capacitors

In this paper atomic‐layer deposition (ALD) HfxAl1–xOy thin films with a wide range of metal components concentrations (x = 0.2−0.8) for metal–insulator–metal (MIM) capacitors were investigated with emphasis on the chemical properties and phase composition. It was shown by X‐ray diffraction (XRD) that all films are amorphous. X‐ray photoelectron spectroscopy (XPS) revealed the same energy position with respect to the valence‐band maximum of Al2p and Hf4f lines and a continuous shift of O1s and O‐KLL lines toward the higher binding energy (0.45 and 2.2 eV, respectively) with increase of Al content. Both the shape and position of O1s and O‐KLL lines indicated the inability to deconvolute it on sublines related to the binary oxides. The calculated modified Auger parameter indicated the change of the ionicity of the bonding in HfxAl1–xOy films with change of the composition. Thus, it was proposed that HfxAl1–xOy films in all the studied composition range represent amorphous solid solutions. The continuous change of energy bandgap measured by reflected electron energy loss spectroscopy (REELS) from ∼6.5 eV for Al2O3 to ∼5.4 eV for HfO2 and XRD data do not contradict this assumption. Correlation between structural properties of HfxAl1–xOy films and electrical properties of MIM capacitors based on them was also shown, that is, continuous change in capacitance density (from 3.1 to 7.4fF/µm2), leakage current density and quadratic voltage coefficient of capacitance with composition change was observed.

Structures, mechanical properties, equations of state, and electronic properties of β-HMX under hydrostatic pressures: a DFT-D2 study.

We report the hydrostatic compression studies of the β-polymorph of a cyclotetramethylene tetranitramine (HMX) energetic molecular crystal using DFT-D2, a first-principles calculation based on density functional theory (DFT) with van der Waals (vdW) corrections. The molecular structure, mechanical properties, electronic properties, and equations of state of β-HMX are investigated. For the first time, we predict the elastic constants of β-HMX using DFT-D2 studies. The equations of state under hydrostatic compression are studied for pressures up to 100 GPa. We found that the N-N bonds along the minor axis are responsible for the sensitivity of β-HMX. The analysis of the charge distribution shows that the electronic charge is transferred from hydrogen atoms to nitro groups with the amount of 0.131 and 0.064e for the nitro groups along the minor axis and major axis, respectively, when pressure changes from 0 GPa to 100 GPa. The electronic energy band gap changes from direct at a pressure of 0 GPa to indirect at a pressure of 50 GPa and higher. The band gap decreases with respect to an increase in pressure, implying that the impact sensitivity increases with compression. Our study suggests that the van der Waals interactions are critically important in modeling the mechanical properties of this molecular crystal.

Modeling on the size dependent properties of InP quantum dots: a hybrid functional study

Theoretical calculations based on density functional theory were performed to provide better understanding of the size dependent electronic properties of InP quantum dots (QDs). Using a hybrid functional approach, we suggest a reliable analytical equation to describe the change of energy band gap as a function of size. Synthesizing colloidal InP QDs with 2–4 nm diameter and measuring their optical properties was also carried out. It was found that the theoretical band gaps showed a linear dependence on the inverse size of QDs and gave energy band gaps almost identical to the experimental values.

Optical Properties of PVA:CdCl2.H2O Polymer Electrolytes

Polymer electrolytes based on Polyvinyl alcohol - Cadmium Chloride were prepared by solution cast technique. Results of optical absorption, transmission spectra, refractive index, optical band gaps, optical conductance, single oscillator energy, dispersion energy, real and imaginary parts of dielectric constants studies are presented. The optical properties were obtained using UV-VIS Double Beam Spectrophotometer in the wavelength range (190-1100) nm. The optical transmittance at wavelength ≈ 190nm for pure PVA was nearly at 78%, while it was 50% for all doped samples. The optical transmittance was increased with increasing wavelength up to 98% for all films beyond ≈240nm. The calculated energy band gap changes from 6.42eV (pure PVA) to 5.80eV (PVA-20%CdCl2.H2O). The optical conductance and band-gap indicated that the films are almost transmitting within the visible range. The single oscillator expression has been used to obtain the information about disorder degree. The real and imaginary parts of dielectric constant of the doped films increases with increasing CdCl2.H2O concentration, and it shows decreases abruptly in the wavelength (200- 220) nm, and finally becomes constant with increase in photon energy.