Energy Position Of Peak Research Articles

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.

The Nonradiative Properties of Self‐Trapped Holes in Ultra‐Wide Bandgap Gallium Oxide Film

The photoluminescence (PL) of self‐trapped holes (STH) in ultra‐wide bandgap β‐Ga2O3 is commonly its most dominant light emission and is an inherent property. Thus, gaining knowledge of the crystal dynamics that impact the PL properties is vital to sensor and other technologies. The PL, Raman‐phonons, and their interactions are studied at an extreme temperature range of 77–622 K. The PL is studied up to the bandgap value of ≈5 eV. It is found that the high‐energy Raman modes provide a major route to the nonradiative process of the PL via STH–phonon interaction with an activation energy of 72 meV. This dynamic is modeled with the configurational coordinate scheme at the strong phonon coupling limit. The exceptionally broad Gaussian PL linewidth manifests this coupling. The weak temperature response of the PL energy peak position indicates that the STH has characteristics of a deep‐level defect. This contrasts with the large redshift of ≈220 meV of the optical gap of the film, ascertained from transmission. Unlike the temperature response of the high‐energy phonons, the behavior of the low‐energy phonons is found to follow the Bose–Einstein population increase, indicating no strong interaction with the STH.

Disentangling doping and strain effects at defects of grown MoS2 monolayers with nano-optical spectroscopy.

The role of defects in two-dimensional semiconductors and how they affect the intrinsic properties of these materials have been a widely researched topic over the past few decades. Optical characterization techniques such as photoluminescence and Raman spectroscopies are important tools to probe the physical properties of semiconductors and the impact of defects. However, confocal optical techniques present a spatial resolution limitation lying in a μm-scale, which can be overcome by the use of near-field optical measurements. Here, we use tip-enhanced photoluminescence and Raman spectroscopies to unveil the nanoscale optical properties of grown MoS2 monolayers, revealing that the impact of doping and strain can be disentangled by the combination of both techniques. A noticeable enhancement of the exciton peak intensity corresponding to trion emission quenching is observed at narrow regions down to a width of 47 nm at grain boundaries related to doping effects. Besides, localized strain fields inside the sample lead to non-uniformities in the intensity and energy position of photoluminescence peaks. Finally, two distinct MoS2 samples present different nano-optical responses at their edges associated with opposite strains. The edge of the first sample shows a photoluminescence intensity enhancement and energy blueshift corresponding to a frequency blueshift for E2g and 2LA Raman modes. In contrast, the other sample displays a photoluminescence energy redshift and frequency red shifts for E2g and 2LA Raman modes at their edges. Our work highlights the potential of combining tip-enhanced photoluminescence and Raman spectroscopies to probe localized strain fields and doping effects related to defects in two-dimensional materials.

Influence of relativistic effects on photoionization process of hydrogen-like ions in plasma environment

In this study, the photoionization cross sections of C<sup>5+</sup>, Al<sup>12+</sup>, and W<sup>73+</sup> ions in a Debye plasma environment are calculated in the dipole approximation. The main emphasis is placed on investigating the influence of relativistic effects on shape resonances, Cooper minima, and virtual state effects. The relativistic effects lead to fine-structure splittings, allowing the appearance of double-shape resonance peaks in the total cross-section. Because the width and energy position of resonance peak are affected by the near critical screening length, the increase of nuclear charge Z leads to the significant differences in the size, width, and position of the double-shape resonance peak. The energy position of Cooper minimum in the photoelectrons is related to the critical screening length corresponding to the final continuum state. Unlike the deeper minima observed in the total photoionization cross-sections for C<sup>5+</sup> and Al<sup>12+</sup> ions, for the higher nuclear charge of W<sup>73+</sup> ions, the significant fine-structure splitting arising from relativistic effects results in substantial differences in the positions of the Cooper minima in the partial cross-sections. Therefore, when superimposed on the total cross section, these minima appear shallower. The W<sup>73+</sup> ion has a higher nuclear charge, and the screening length related to the virtual state effect is completely different from that of C<sup>5+</sup> ion and Al<sup>12+</sup> ion. Moreover, for the same screening length, there is a significant difference in the virtual state enhancement amplitude between C<sup>5+</sup> ion and Al<sup>12+</sup> ion in the low energy region .

High-temperature photoluminescence properties of various defects in hydrothermally grown ZnO microrods

High-temperature photoluminescence properties of hydrothermally grown ZnO microrods were reported. Photoluminescence spectra of ZnO microrods deconvoluted into three Gaussian components: near band edge (NBE) emission, Violet emission (VL) and Yellow emission (YL) peaks corresponding to free excitons, zinc vacancies and interstitial oxygen atoms, respectively. Increasing the temperature caused a redshift of the energy position of the NBE and VL peaks and a blueshift of the energy position of the YL peak were observed. In the temperature range from 300K to 473K, the intensities of the NBE and VL bands varied based on a nonlinear pattern. Intensity of these emission bands decreases from temperature 473K–673K. As the temperature increases, changes in the energy and crystal structures of the material due to decrease in the concentration of defects cause a blueshift of the emission bands related to interstitial atoms, and a redshift of the emission bands related to vacancies.

Effect of pulse duration on the above-threshold ionization of a hydrogen atom irradiated by a 400 nm intense laser.

The photoelectron emission spectra generated by the interaction between ultrashort intense laser pulses and atoms can reveal the ultrafast dynamics of electrons. By using the numerical solution of the time-dependent Schrödinger equation in momentum space, the photoelectron emission spectra of atoms irradiated by 400 nm intense lasers with different durations of the pulse has been investigated. In the photoelectron emission spectrum, in addition to the above-threshold ionization peaks due to ionization interference in multiple cycles and the sideband peaks mainly due to the interference of ionized electrons at different moments along the rising edge of the laser pulse envelope, additional peaks of photoelectron emission whose intensity appears to oscillate with the increasing duration of the laser pulse can also be observed. Based on strong-field approximation and the population's analysis of the bound state, it is found that these photoelectron peaks originate from the ionization of the excited state and the oscillations of these peaks are due to the superposition of their peak energy positions with the sideband energy positions. Furthermore, it is demonstrated that the energy positions of the maximum intensity of the photoelectron emission spectra move towards the higher energy end as the duration of the driving laser pulse extends. This phenomenon can be attributed to the fact that the main moment of ionization of atoms changes with the increasing duration of the driving laser pulse, thus allowing the real-time ionization of atoms to be probed using photoelectron emission spectra.

Trap sensitivity of splitted source Z Shape horizontal pocket and hetero stack TFETs: a simulation study

This paper reports the trap sensitivity analysis of split source horizontal pocket Z shape tunnel field effect transistor (ZHP-TFET) and hetero stack TFET (HS-TFET) using technology computer aided design (TCAD) simulator. The sensitivity analysis elaborates the significance of ideal trap charges at the interface of oxide and semiconductor material for both acceptor and donor like traps. The trap sensitivity analysis is highlighted for variation in trap-concentrations, temperature, gate-metal work function, and peak energy position, for both the TFETs. Furthermore, we have implemented digital inverter on taking into account the interface trap charges effect. Result reveals that tarp sensitivity on various electrical parameter of HS-TFET is significantly higher than ZHP-TFET. It is seen that ZHP-TFET provides sensitivity around 11 and 33 under acceptor and donor impurities, respectively, whereas, for HS-TFET sensitivity is around 22 and 60 for acceptor and donor impurities, respectively, for wide variation in trap concentration. The voltage transfer characteristic and voltage gain of digital inverter are improved by observable amount in ZHP-TFET than HS-TFET for both donor and acceptor like trap. The noise margin of ZHP-TFET based resistive inverter comes 0.75 V, 0.73 V, and 0.77 V, while in case of HS-TFET these value noted as 0.32 V, 0.13 V and 0.37 V under consideration for no trap, acceptor trap, and donor trap, respectively.

The native and metastable defects and their joint density of states in hydrogenated amorphous silicon obtained from the improved dual beam photoconductivity method

In this study, undoped hydrogenated amorphous silicon (a-Si:H) thin films deposited under moderate dilution ratios of silane by radio frequency plasma-enhanced chemical vapor deposition (RF-PECVD) have been investigated using steady-state photoconductivity and improved dual beam photoconductivity (DBP) methods to identify changes in multiple gap states in annealed and light-soaked states. Four different gap states were identified in annealed state named as A, B, C, and X states. The peak energy positions of these Gaussian distributions are consistent with those recently identified by Fourier transform photocurrent spectroscopy (FTPS). After in situ light soaking, their density increases with different rates as peak energy positions and half-widths remain unaffected. The electron-occupied A and B states located below the dark Fermi level and their density and ratios in the annealed and light-soaked states correlate well with those defects detected by time-domain pulsed electron paramagnetic resonance (EPR) experiments. The A, B, and X states located closer to the middle of the bandgap anneal out at room temperature in dark and define the “fast” states. However, the C states show no sign of room temperature annealing such that they must define the “slow” states in undoped a-Si:H. The results found in this study indicate that the anisotropic disordered network is a more appropriate model than previously proposed defect models based on the continuous random network to define the nanostructure of undoped a-Si:H, where multiple defects, D0 and non-D0 defects, can be identified by using the improved DBP method.

Design and manufacture of scintillation detector using CsI(Tl) crystal coupled with silicon photomultipliers

In this research, a scintillation detector was developed using the CsI(Tl) scintillator crystal coupled with a silicon photomultiplier (SiPM) to replace the photomultiplier tube (PMT), resulting in a compact and energy-efficient detector. A rectangular box-shaped CsI(Tl) scintillation crystal with dimensions of 50x25x25 mm from Kinheng and a SiPM module S13361-3050AE-08 with dimensions of 25x25 mm from Hamamatsu were selected to use. The preamplifier circuit, power supply, and temperature stabiliser have also been integrated into the detector. The characteristics of this detector were evaluated using a 137Cs standard radioactive source together with Ortec’s multichannel analyser device and Gamma Vision software for spectrum analysis. Results showed that the energy resolution for the 137Cs peak of this detector is about 8.03%, which is almost equivalent to the energy resolution of 7.87% of the Canberra detector using 76x76 mm NaI(Tl) crystal coupled to the PMT. The results of the evaluation of stability over time when the operating ambient temperature of this detector with no change showed that the energy peak position and the energy resolution for the 137Cs radioactive source are almost unchanged. The research also investigated the stability of the detector according to the operating ambient temperature. The results exhibited that the output pulse amplitude varies greatly with the ambient temperature, it decreases when the temperature increases and vice versa. Under the condition that the operating ambient temperature varies from 11oC to 50oC, the energy peak position of 137Cs changes were 1762 and 167 channels, respectively in the cases without and with adjustment of output pulse amplitude stabilisation function in power supply for SiPM. When there is a function of output pulse amplitude stabilisation, the change in peak position according to operating ambient temperature is still about 4.3 channels/oC, so further research is needed to correct the influence of ambient temperature on the operation of this detector, to provide wide applicability of scintillation detector using SiPM to replace traditional PMT in the future.

Effect of site geometry on oxygen K, and silver and gallium L2,3 energy loss spectra of AgGaO2 polymorphs: A DFT study

By means of the ab initio calculations of the electron density of states and energy loss near edge structure (ELNES) analysis, the present study examines the effect of local coordination and site symmetry on the electron energy structure of AgGaO2 polymorphs. Difference in spectral dispersion and the energy peak positions of the O K, and Ag and Ga L2,3 ELNES spectra of three AgGaO2 polymorphs is attributed to the difference in local coordination, bond length, site symmetry, and electronic structure of the structures. In order to reproduce the edge spectra, it is inevitable to consider the core hole effect in calculations.

Tunable light trapping in the graphene metasurface.

Graphene metasurfaces based on surface plasmon resonance can greatly enhance the interaction between light and matter at the nanoscale. At present, the resonance of graphene metasurfaces is widely used to enhance the absorption of atomic layer graphene, but little work has focused on the light field trapping capabilities it brings. In this paper, we numerically study the light trapping and manipulation of an asymmetric graphene metasurface. The designed device supports two resonant modes, and the multipole decomposition confirms that the electric dipole response dominates them. The calculated average electric field enhancement factor (EF) can reach 1206 and 1779, respectively. The near-field distribution indicates that the electric field is mainly localized in the graphene nanodisks. When the Fermi energy changes, the intensity and peak position of EF can be effectively regulated. In addition, when the polarization of the incident light is adjusted, the light field capture of the two modes is independently regulated. These results reveal that the graphene metasurface has significant light field capture and regulation ability, which provides a new idea for the realization of active regulation of high-performance low-dimensional optical devices.

Spectroscopic characterization of a new series of bismuth tantalate pyrochlores doped with 3d-ions

X-ray spectroscopy methods (XPS, NEXAFS) were used to study the electronic state of the ions that make up pyrochlores (sp. gr. Fd-3m, No. 227) Bi2Mg1-xMxTa2O9+Δ (M − Cr,Mn,Fe,Co,Ni,Cu). It has been established that doping of bismuth magnesium tantalate pyrochlore with 3d-ions does not affect the electronic state of bismuth and magnesium ions, which are found in the ionic form Bi(+3), Mg(+2). Tantalum ions are in the same charge state Ta(+5-δ) due to the characteristic shift of the energy position of peaks towards the lower energies compared to the binding energy in pentavalent tantalum oxide. An energy shift in the Ta4f and Ta5p spectra is observed for all transition ions without a strict regularity in the magnitude of the signal shift depending on the nature of the dopant. Ions of some 3d-elements in the composition of pyrochlores, according to X-ray spectroscopy, have several oxidation states, for example, Cu(+1,+2), Co(+2,+3), Mn(+2,+3), Cr(+3,+6). The iron and nickel ions predominantly have the +3 and + 2 oxidation states, respectively.

Radio-frequency biasing of ion acceleration grids with different propellants

In order to ensure the space charge compensation of the plume, conventional ion thrusters need an additional neutralizer to release electrons. When a radio-frequency (RF) voltage is applied across the grid system instead of a direct-current voltage, the simultaneous extraction of ions and electrons is achieved, thereby a neutralizer is not required. In this paper, based on the non-uniform distribution of neutral gas density calculated using the angular coefficient method, the particle-in-cell Monte Carlo collision method is used to thoroughly investigate the spatial and temporal dynamics of particles and the grid system performance for different propellants (argon, krypton and xenon) in such an RF grid system. RPA and E × B probe are employed to measure the ion flux distribution functions (IFDFs) of RF ion thruster with RF biasing, which are used to compare with the simulations. The simulated linear relationship between the self-bias voltage and the RF voltage amplitude and the multi-peak behavior of IFDF under low RF frequency conditions are comparable with the experimental data. The simulated IFDFs compare well with the experiments with the deviation of energy peak position less than 7% and 10% from those by RPA and E × B probe respectively, indicating the effectiveness of the used model. Simulations show the RF grid system is able to realize the extraction of electrons for all three propellants, so as to achieve the plume neutralization without an external neutralizer through the spatial and temporal oscillations of the beams. Electrons pass through the grid twice (extracted from the upstream, and backflow from the downstream), bringing two peaks of electron current to the accelerator grid in one period. The thrust-RF voltage curves for all three propellants show obvious slope transition, when the perveance limit is reached. The low-energy ions in the plume are mainly generated by the electron impact ionization processes for Xe while by CEX collisions for Ar. A larger ion current density of Xe on the downstream surface of the accelerator grid, which may lead to possibly more serious erosions of grids, is found compared with those of Kr and Ar. This is mainly contributed by the larger density of electron impact ionization generated ions of Xe in the downstream because Xe propellant has a larger electron density and ionization cross-section.

Advanced inorganic halide ceramic scintillators

Research in ceramic scintillators has steadily progressed alongside the research in bulk single crystal scintillator growth. As interest in faster scintillation material production with lower cost increases, more research on scintillating ceramics is needed. Research targeting optimization of optically transparent ceramics that can rival bulk-grown crystals grown may lower cost, increase yield, increase volume, and improve energy resolution in applications and systems currently using sodium iodide and alike. Ceramic scintillators that are dense (>5 g/cm3), have high effective Z (>60), are bright (>40,000 photons/MeV), and are not sensitive to moisture as well as those that can be handled without protection are desired. Ultra-fast ceramic materials are also of interest. This paper presents an equipment design and technique to produce inorganic halide ceramic scintillators Cs2HfCl6 (CHC) and Tl2HfCl6 (THC). Improvements and optimization of CHC and THC ceramic scintillator fabrication are gauged by monitoring the energy resolution and peak position of 137Cs full energy peak at 662 keV. With a 1-inch diameter CHC ceramic scintillator, energy resolution of 5.4% (FWHM) and light yield of 20,700 ph/MeV are achieved, while with a 16-mm diameter THC ceramic scintillator, energy resolution of 5.1% (FWHM) and light yield of 27,800 ph/MeV are achieved. Decay times of 0.6 microseconds (21%) and 3.0 microseconds (79%) are measured for CHC and 0.3 microseconds (13%) and 1.0 microseconds (87%) for THC. Both ceramic CHC and THC scintillators have similarly good proportionality data when compared to their single crystal counterparts.

Alpha particle detector with planar double Schottky contacts directly fabricated on semi-insulating GaN:Fe template* *Project supported by the Natural Science Foundation of Jiangsu Province, China (Grant Nos. BK20190302 and BK20201253).

Alpha particle radiation detectors with planar double Schottky contacts (DSC) are directly fabricated on 5-μm-thick epitaxial semi-insulating (SI) GaN:Fe film with resistivity higher than 1 × 108 Ω ⋅cm. Under 10 V bias, the detector exhibits a low dark current of less than 5.0 × 10−11 A at room-temperature, which increases at higher temperatures. Linear behavior in the semi-log reverse current–voltage plot suggests that Poole–Frenkel emission is the dominant carrier leakage mechanism at high bias. Distinct double-peak characteristics are observed in the energy spectrum of alpha particles regardless of bias voltage. The energy resolution of the SI-GaN based detector is determined to be ∼ 8.6% at the deposited energy of 1.209 MeV with a charge collection efficiency of ∼ 81.7%. At a higher temperature of 90 °C, the measured full width at half maximum (FWHM) rises to 235 keV with no shift of energy peak position, which proves that the GaN detector has potential to work stably in high temperature environment. This study provides a possible route to fabricate the low cost GaN-based alpha particle detector with reasonable performance.

Luminescence properties of hexagonal boron nitride powders probed by deep UV photoluminescence spectroscopy.

Deep ultraviolet (UV) photoluminescence (PL) spectroscopy was employed to study the luminescence properties of hexagonal boron nitride (h-BN) crystal powders after annealing the samples at different temperatures in the range of 100–900 °C for 1 h in ambient air. The PL spectrum from the h-BN powder samples annealed around 700 °C showed strong luminescence intensity at 5.49 eV along with enhanced phonon-assisted band-edge emission at 5.90 eV. Additionally, it revealed sharp atomic-like emission lines in UV region at 4.10, 4.12, 4.14, and 4.16 eV with line widths less than 1 nm from the annealed samples which were not present in the unannealed samples. Power- and temperature-dependent PL measurements of the sharp atomic-like emission lines exhibited robust nature of the energy peak positions. Based on the theoretical reports, the sharp emission lines could be carbon-related defects.

Nitrogen induced localised-state ensemble effect on multi quantum well GaInNAs with low indium concentration

In this paper, temperature dependence photoluminescence has been taken on two multi-quantum well GaInNAs, with low indium composition and the impact of percentage nitrogen incorporation ⩽1%. The variation of peak energy position, linewidth, and integrated intensity emission have been investigated by adopting a localised state ensemble model to anticipate the dissimilar spontaneous emission mechanisms of the two samples. A good agreement has been observed between theoretical analysis and experimental data and enriches the understanding of the design and provides improvement opportunities for future GaInNAs based optoelectronic devices for biomedical applications.

Identification of Excitons and Biexcitons in Sb2Se3 under High Photoluminescence Excitation Density

AbstractThe near‐band‐edge emission of Sb2Se3 microcrystals is studied in detail under high photoluminescence excitation density using a pulsed UV laser (λ = 266 nm, pulse width 0.6 ns). Based on the peak energy positions and the excitation power density and temperature dependencies (T = 3–110 K) of the photoluminescence spectra, the emission is interpreted as a recombination of two pairs (A and B) of free excitons and biexcitons appearing because of valence band splitting. The magnitude of the valence band splitting due to the crystal field (Δcr = 20–22 meV) is estimated in the Brillouin zone center. At T = 3 K, the A and B biexciton emission at 1.302 and 1.322 eV, respectively, and the A and B free exciton emission at 1.311 and 1.333 eV, respectively, are observed. The binding energy of A and B biexcitons is 9 and 11 meV, respectively, and the binding energy of A free exciton is 6 meV. The activation energy of thermal quenching for all observed peaks is 20 meV.

From InGaN pyramids to micro-LEDs characterized by cathodoluminescence

We present a study of the optical properties of various steps in the process of fabricating micro light-emitting diodes (μ-LEDs) based on quantum wells embedded in micron-sized InGaN platelets. In this study, we focus on structures for red emission, but the technology is equally suitable for the less technologically challenging blue and green emitting μ-LEDs. The starting point is growth of an InGaN pyramid with a sub-micron sized hexagonal base. The pyramid is flattened to create a flat top c-facet for the subsequent InGaN quantum well growth. We compare two approaches, reshaping of the pyramid by high-temperature annealing; and by chemical mechanical polishing. Their merits are discussed. The flattened platelets are used as templates to grow low-strain single quantum wells in both heterostructures and full LEDs including n- and p-barriers on either side of the quantum well. The structures are investigated in terms of homogeneity in peak energy position and intensity using hyperspectral cathodoluminescence imaging. We observe that the main contribution to inhomogeneity is the growth of the initial pyramid, that exhibits regular, facet driven variations in the In incorporation.

Calculation of the Bandgap of Dilute Nitride GaAsSbN Alloys

Dilute nitrides are semiconductor alloys, obtained from the conventional III-V compounds by incorporating a small amount of nitrogen. In this work, we focus on GaAsSbN considered as a perspective material for incorporation in multijunction solar cells. Nitrogen creates a localized level inside the conduction band continuum. The interaction of this level with the conduction band is usually described by the single band anti-crossing (BAC) model. The double BAC model of GaAsSbN considers both the N and the Sb localized levels in the conduction and the valence band, respectively. We calculate the bandgap energy of GaAsSbN employing the double BAC model for different concentrations of Sb and N. Parameters of the BAC model taken from different literature sources are used in the calculations and their influence on the final result is explored. Finally, the calculated bandgap energies are compared to experimental data of GaAsSbN layers grown on n-GaAs substrates by low-temperature liquid phase epitaxy. These data include the optical absorption edge of the material determined by surface photovoltage spectroscopy and the energy position of the photoluminescence peak at room temperature.