Lattice Temperature Effects Research Articles

Practical consideration on Racah parameter and Tanabe−Sugano diagram analyses for Mn4+ and Cr3+-activated phosphors

The Racah parameters and Tanabe−Sugano (T−S) diagram are widely used as describing the electron−electron repulsion effects within the metal complexes in coordination chemistry. The present study discusses the Racah and related parameters for the Mn4+ and Cr3+-activated phosphors. The main subjects are two-fold: (i) to clarify how different input parameters of the excited-state energies make a difference in the Racah parameters derived from the general model and (ii) to further clarify the differences between the general and our newly proposed models. The three different excited-state energies of (1) the zero-phonon line energy, (2) the photoluminescence (PL) and/or PL excitation (PLE) peak energies, and (3) the Stokes shift-corrected PLE peak energy are considered in (ii). It is shown that the choice of such excited-state energies is of crucial importance for obtaining reliable Racah parameters and T−S diagram. The present analysis of (ii) also suggests our newly proposed model to promise the Racah parameters being satisfied the requirements of B and C to be smaller than and their ratio of C/B being not largely changed from the free-ion values. The lattice temperature effects on the PL and PLE spectral features of the 3d3 ion-activated phosphors are also discussed in detail.

Physical Insights into Vacancy-Based Memtransistors: Toward Power Efficiency, Reliable Operation, and Scalability.

Memtransistors that combine the properties of transistor and memristor hold significant promise for in-memory computing. While superior data storage capability is achieved in memtransistors through gate voltage-induced conductance modulation, the lateral device configuration would not only result in high write bias, which compromises the power efficiency, but also suffers from unsuccessful memory reset that leads to reliability concerns. To circumvent such performance limitations, an advanced physics-based model is required to uncover the dynamic resistive switching behavior and deduce the key driving parameters for the switching process. This work demonstrates a self-consistent physics-based model which incorporates the often-overlooked effects of lattice temperature, vacancy dynamics, and channel electrostatics to accurately solve the interaction between gate potential, ions, and carriers on the memristive switching mechanism. The completed model is carefully calibrated with an ambipolar WSe2 memtransistor and hence enables the investigation of the carrier polarity effect (electrons vs holes) on vacancy transport. Nevertheless, the validity of the model can be extended to different materials by a simple material-dependent parameter modification. Building upon the existing understanding of Schottky barrier height modulation, our study reveals three key insights─leveraging threshold voltage shifts to lower write bias; optimizing lattice temperature distribution and read bias polarity to achieve successful memory state recovery; engineering contact work function to overcome the detrimental parasitic current flow in short channel ambipolar memtransistors. Therefore, understanding the significant correlation between the switching mechanisms, different material systems, and device structures allows performance optimization of operating modes and device designs for future memtransistors-based computing systems.

Modeling of Classical Channel Hot Electron Degradation in n-MOSFETs Using TCAD

A technology CAD (TCAD) setup is used to calculate the channel hot electron (CHE) induced parametric drift in n-MOSFETs. The setup uses reaction-diffusion-drift model and utilizes carrier energy, vertical electric field, and lattice temperature effects, to calculate the time kinetics of trap generation and its impact on the device parametric drift. Experimental data from published reports, measured using different probes, for midgate bias stress under varying drain bias ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 3$ </tex-math></inline-formula> –8 V) and temperature (0 °C–100 °C) are modeled, in classical devices having different channel lengths (2.0– <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.3~\mu \text{m}$ </tex-math></inline-formula> ) and oxide thicknesses (35–5 nm). The impact of device dimension scaling on the spatial distribution of generated traps and their impact on the device parametric drift are discussed.

Franck-Condon relaxation in photo-excited YAG:Ce studied using real-time time-dependent density functional theory

First-principles calculations of electron-ion dynamics based on real-time time-dependent density functional theory were performed to study the lattice dynamics in yttrium aluminum garnet (YAG) doped with cerium (Ce) following photoexcitation. The dynamics induced by the optical transitions from the valence band to the conduction band of the YAG host and from the Ce 4f to 5 d levels were examined. Significant lattice motion was observed in the latter case. This lattice motion (Franck-Condon relaxation) decreased the Ce–O bond length by 0.05 Å and increased the energy of the Ce 4f level by 0.5 eV, suggesting a Stokes shift in the light emission due to the Ce 5 d→4f transition. The calculated Stokes shift is consistent with the recently reported experimental value, despite the approximations used in the present calculations. The effect of lattice temperature was also examined up to 300 K.

Investigation of modulation transfer function in InGaAs photodetector small pitch array based on three-dimensional numerical analysis

Three-dimensional numerical simulation technology was used to investigate the influence of structural and material parameters on the modulation transfer function (MTF) of lattice matched InGaAs/InP planar small pitch arrays. We found that extending depletion zone through increasing depth of diffusion junction and reducing the doping concentration in the absorption layer plays a critical role in optimizing the MTF of arrays. And it is highly worth noting that the very optimization effects become even more pronounced in smaller pitch arrays, which offers valuable references to restrain crosstalk in highly dense array and strengthen the imaging ability of large format photodetector system in future. However, the inevitable cost of deteriorating the specific detectivity should not be ignored. And hence, junction depth and doping concentration of the absorption layer need to be balanced in actual preparation. In addition, the effects of lattice temperature on MTF and crosstalk in arrays were also discussed. The inter-pixel crosstalk deteriorates seriously as rising lattice temperature. A stronger impact of lattice temperature on MTF of larger pitch arrays has been confirmed. This work offers important reference to suppress inter-pixel crosstalk in obtaining the high-resolution imaging for InGaAs photodetector focal plane array.

Dependence of limited radiative recombination rate of InGaN-based light-emitting diode on lattice temperature with high injection**Project supported by the National Natural Science Foundation of China (Grant Nos. 51602141, 11674147, 61604066, 11604137, and 21405076), the National Key Research and Development Project of China (Grant Nos. 2016YFB0400600 and 2016YFB0400601), and the Key Research and Development Project of Jiangxi Province, China (Grant No.

It is observed that the radiative recombination rate in InGaN-based light-emitting diode decreases with lattice temperature increasing. The effect of lattice temperature on the radiative recombination rate tends to be stable at high injection. Thus, there should be an upper limit for the radiative recombination rate in the quantum well with the carrier concentration increasing, even under the same lattice temperature. A modified and easily used ABC-model is proposed. It describes that the slope of the radiative recombination rate gradually decreases to zero, and further reaches a negative value in a small range of lattice temperature increasing. These provide a new insight into understanding the dependence of the radiative recombination rate on lattice temperature and carrier concentration in InGaN-based light-emitting diode.

Analysis of DC Characteristics in GaN-Based Metal-Insulator-Semiconductor High Electron Mobility Transistor with Variation of Gate Dielectric Layer Composition by Considering Self-Heating Effect

This study investigates metal-insulator-semiconductor high electron mobility transistor DC characteristics with different gate dielectric layer compositions and thicknesses, and lattice temperature effects on gate leakage current by using a two-dimensional simulation. We first compared electrical properties, including threshold voltage, transconductance, and gate leakage current with the self-heating effect, by applying a single Si3N4 dielectric layer. We then employed different Al2O3 dielectric layer thicknesses on top of the Si3N4, and also investigated lattice temperature across a two-dimensional electron gas channel layer with various dielectric layer compositions to verify the thermal effect on gate leakage current. Gate leakage current was significantly reduced as the dielectric layer was added, and further decreased for a 15-nm thick Al2O3 on a 5-nm Si3N4 structure. Although the gate leakage current increased as Al2O3 thickness increased to 35 nm, the breakdown voltage was improved.

Electronic Theory of Ultrafast Spin Dynamics in NiO

Electronic Theory of Ultrafast Spin Dynamics in NiO NiO is a good candidate for ultrafast magnetic switching because of its large spin density, antiferromagnetic order, and clearly separated intragap states. In order to detect and monitor the switching dynamics, we develop a systematic approach to study optical second harmonic generation (SHG) in NiO, both at the (001) surface and in the bulk. In our calculations NiO is modeled as a doubly embedded cluster. All intragap d-states of the bulk and the (001) surface are obtained with highly-correlational quantum chemistry and propagated in time under the influence of a static magnetic field and a laser pulse. We find that demagnetization and switching can be best achieved in a subpicosecond regime with linearly rather than circularly polarized light. We also show the importance of including an external magnetic field in order to distinguish spin-up and spin-down states and the necessity of including magnetic-dipole transitions in order to realize the process in the centrosymmetric bulk. Having already shown the effects of phonons in the SHG for the bulk NiO within the frozen-phonon approximation, and following the same trail of thoughts, we discuss the role of phonons in a fully quantized picture as a symmetrylowering mechanism in the switching scenario and investigate the electronic and lattice temperature effects.

Determination of transient atomic structure of laser-excited materials from time-resolved diffraction data

The time evolution of the Bragg peaks of photo-excited gold nanofilms is measured using transmission ultrafast electron diffraction (UED) with 3.0 MeV electron pulses and the corresponding structure evolution is calculated using two-temperature molecular dynamics (2T-MD). The good agreement obtained between the measured and calculated Bragg peaks, over the full experimental timescale, enables the lattice temperature effects and the structural changes to be disentangled for the first time. The agreement demonstrates that 2T-MD is a reliable method for solving the inverse problem of structure determination of laser irradiated metals in UED measurements.

Analysis of Lattice Temperature Effects on a GaInP/6H-SiC Strained Quantum-Well Lasers

In this paper, simulative study on the effects of lattice temperature on a GaInP/6H-SiC strained quantum-well (QW) laser's device is presented. Loss mechanisms are severe in the edge-emitting lasers. As a consequence, the wall-plug efficiency is sensitive to changes in temperature. The lasers used in this work were separate-confinement quantum-well lasers with a single strained GaInP, located in a latticematched waveguide core and cladding region of 6H-SiC. This paper provides the key results of the wall-plug efficiency upon the lattice temperature.

Long-wavelength MQW Vertical-cavity Surface Emitting Laser: Effects of Lattice Temperature

The lattice temperature in a 1.5 μm wavelength InP-based vertical-cavity surface-emiting laser (VCSEL) was varied between 273 K until 353 K using an industrial-based numerical simulator and its effects on the characteristics of the device was analysed. The temperature fluctuation has a direct effect on the gain distribution, causes a peak wavelength shift and is the precursor for various dark current processes within the laser. The device employs InGaAsP multi-quantum wells (MQW) sandwiched between GaAs/AlGaAs and GaAs/AlAs distributed Bragg reflectors (DBRs). The thermal resistance used to model the electrical contacts causes an approximate 13 K temperature rise above the ambient temperature (300 K) at a bias of 3 V and a 50 % increase in the threshold current is observed with temperature increment. Various heat sources elements within the VCSEL device were also analysed upon increment of lattice temperature.

High lattice temperature effects on the ultrafast electron transport in 4H-SiC

High lattice temperature effects on the electron transport transient in the 4H-SiC c-parallel direction are studied within a single equivalent isotropic valley picture in the momentum and energy relaxation time approximation. The ultrafast transport regime occurs in a subpicosecond scale (&amp;lt;0.2ps), during which an overshoot in the electron drift velocity starts to be evident for high electric fields (≳60kV∕cm), depending on the lattice temperature. An increase of the electric field strength shifts the overshoot peak of the electron drift velocity to an earlier time. For a strong enough electric field, a higher lattice temperature cannot eliminate the electron drift overshoot effect, but can reduce it considerably due to a stronger electron-phonon scattering.

Channel thermal noise of SOI MOSFET in high-frequency region

An accurate thermal noise model to predict the HF noise performance of submicron SOI MOSFETs is developed in which the effect of lattice temperature and channel length modulation is taken into consideration in addition to the hot electron effect. In the analysis, the lattice temperature dependent mobility has been used to evaluate the spectral density of drain current noise. The results so obtained are compared with the experimental data and are in good agreement.

Terahertz self-oscillations in negative-effective-mass oscillators

We have theoretically investigated spatiotemporal current patterns and self-oscillating characteristics of negative-effective-mass (NEM) p +pp + diodes. Periodically oscillating current densities are presented as a gray density plot, showing rich patterns with the applied bias and doping concentration as controlling parameters. Such a pattern arises in the NEM p-base with a “N-shaped” velocity–field relation. Two-dimensional applied bias-doping concentration phase diagrams at different lattice temperatures are calculated in order to visualize the effect of lattice temperature on the self-oscillating regions. It is indicated that both the applied bias and the doping concentration strongly influence the patterns and self-oscillating frequencies, which are generally in the terahertz (THz) frequency band. The NEM p +pp + diode may therefore be used to develop a electrically tunable THz-frequency oscillator.

The Effect of Lattice Temperature on Abnormal Subgrain Growth Simulations using a Monte Carlo Technique

Abnormal subgrain growth occurs in single-phase materials when the structure contains special subgrains that have growth advantage compared to others in their vicinity by virtue of having unique boundary properties such as low energy and high mobility. Monte Carlo simulations of abnormal subgrain growth were carried out for a wide range of such abnormal growth conditions. For a given abnormal growth condition, the simulation results were found to be sensitive to the choice of the lattice temperature used. When the lattice temperature was too low, the growth kinetics and the shape of the abnormal grain was influenced by the lattice geometry. At higher lattice temperatures, the lattice effects were reduced but the simulation results were scattered around the theoretical prediction of the maximum stable size ratio of the abnormal subgrain to the matrix subgrain. Simulations in which the local lattice temperature was scaled according to the relative boundary energy appeared to reduce the scatter associated with constant lattice temperature simulations, but a discrepancy between theory and simulation was noticed, with the simulations predicting consistently lower values than theoretical. Further simulations with larger system sizes are required in order to better understand the mesoscale issues associated with abnormal subgrain growth.

Temperature-dependence of defect creation and clustering by displacement cascades in α-zirconium

Molecular dynamics (MD) modelling has been employed to investigate the effect of lattice temperature on the production of vacancies and interstitials in the primary damage process of displacement cascades with energy up to 20 keV in α-zirconium. The final number of Frenkel pairs decreases with increasing temperature due to the increase in lifetime of the thermal spike at high temperature. The production efficiency behaves in a similar fashion to that simulated at 100 K, but it is reduced further and saturates at about 20% over the energy range considered at 600 K. The number and size of clusters, both vacancy and interstitial, are increased by increasing PKA energy, and the fraction of interstitials in clusters also increases with increasing lattice temperature. The interstitial clusters can glide back and forth by one-dimensional migration along the crowdion direction at 100 K, but small clusters of less than four SIAs can change their glide direction on and off basal-planes at 600 K. It is also observed that single interstitials and some small clusters can migrate along both 〈1 1 2 ̄ 0〉 and 〈 2 ̄ 2 0 3〉 directions at 600 K. Clusters containing up to 25 interstitials and 24 vacancies were formed by 20 keV cascades at 600 K, and almost all of the clusters have the form of a dislocation loop with Burgers vector 1/3〈1 1 2 ̄ 0〉 . It was found that the 25-interstitial cluster is glissile and dissociates on the basal and prism-planes that form its glide cylinder. Collapse of the 24-vacancy cluster to a perfect vacancy dislocation loop was found to occur in the primary damage process due to the longer lifetime of the thermal spike at higher temperature. The results are discussed in terms of experimental data and compared with those simulated at 100 K.

An analytical model for fully depleted single gate SOI MOS transistors including lattice temperature effects

An analytical model for fully depleted SOI MOSFETs is presented. Major small geometry effects such as carrier velocity saturation, mobility degradation, channel length modulation, and drain induced barrier lowering are included. Device self heating due to low thermal conductivity of a buried oxide layer is included in carrier mobility modelling. Thermal effects are also included in threshold voltage expression. Source, drain, and channel resistance effects are also included. Modelled results are then compared to available measured data and are shown to be in very good agreement.

High-temperature effects on the velocity overshoot of hot electrons in 6H- and 3C-SiC

Lattice temperature effects on the high-field transport transient of electrons in 6H- and 3C-SiC during the subpicosecond regime are studied. The calculations are performed considering a nonparabolic band structure, and the results are obtained through the numerical solution of Boltzmann-like transport equations for the electron drift velocity v and energy within the momentum and relaxation time approximations, p and , respectively. It is shown that an increase of the lattice temperature reduces both the electron drift velocity and energy, being even able to preclude a drift velocity overshoot in 6H- and 3C-SiC. For a given electric field, the growth rate of the electron energy decreases strongly when the 6H- and 3C-SiC lattice temperatures are raised.

A molecular dynamics study of displacement cascades in α-iron

The mechanisms of defect production in displacement cascades in α-iron have been investigated by computer simulation. Cascades of up to 5 keV in energy have been simulated by molecular dynamics in crystals with atomic interactions described by a many-body potential. The effects of lattice temperature have been studied by using block temperatures of either 100 or 600 K. 80 cascades have been modelled overall. The morphology of cascades during the collisional phase changes at about 1–2 keV, due to the collective nature of atomic displacements at higher energy. This transition is reflected in the relaxation time during the subsequent recombination phase, and it also decreases the efficiency factor for defect production. This factor is similar in size to that obtained from recent modelling of copper, an fcc metal. Although the cascade zone contains a large number of displaced atoms, true melting was not observed in α-Fe, and vacancy clustering did not occur in the thermal spike phase. Interstitial clustering has been analysed, and found to be less pronounced than in copper. One large cluster was observed to grow by interstitial movement during the thermal spike, and visual analysis has shown that it formed a perfect dislocation loop: it was not nucleated by the Eyre-Bullough mechanism, however. Statistics on the cascade parameters are presented, and comparisons with work on other crystal structures are drawn where possible.

A non-isothermal device simulator for MOSFET analysis

A nonisothermal semiconductor device simulator is developed which solves not only the conventional drift-diffusion equations but also the energy balance and heat flow equations to account for nonequilibrium transport phenomena and lattice temperature effects. The results are compared with the conventional drift-diffusion model. In order to reduce computation time, the heat flow equation is solved by an iterative scheme where this equation is solved only once during three cycles of the iteration loop. It is found that heat generation abruptly increases in the vicinity of the drain and the channel interface, and the lattice temperature shows a localized increase of about 20 degrees in a MOSFET with a channel length of 0.3 mu m, under a bias of V/sub G/=V/sub D/=3.0 V. The electron density distribution spread is broader than with that of the drift-diffusion model-that is, the channel depth becomes wider than in a conventional case. >