Lattice Temperature Distribution Research Articles

Analysis of carrier dynamics and thermal effect of the GaAs photoconductive semiconductor switch in lock-on mode

Abstract The lock-on effect of the gallium arsenide photoconductive semiconductor switch (GaAs PCSS) at repetition rate aggravates the current crowding and electric field distortion, which significantly increases the risk of switch damage or even failure. Therefore, it is of great significance to investigate the carrier transport and the heat generation mechanism for improving the performance and longevity of GaAs PCSS in lock-on mode. The internal physical process of an opposed-electrode GaAs PCSS at low optical energy and strong electric field is analysed and discussed by experiment and simulation. A device-circuit hybrid simulation is employed to investigate the transient electric field, carrier concentration, and lattice temperature distribution within the GaAs PCSS in lock-on mode. The device temperature exhibits a positive correlation with the applied bias electric field, resulting in a peak temperature of 1037.25 K at an electric field of 38 kV/cm. The temperature distribution within the GaAs PCSS indicates a greater possibility for thermal breakdown and damage near the electrodes.

Atomistic analysis on implantation effects of hydrogen ions and copper ions into 4H-SiC

The microstructure evolution of 4H-SiC under the implantation of hydron ions and copper ions was investigated using molecular dynamics (MD) simulations and experimental analysis. MD models were developed to simulate the implantation of single Cu2+ and H+ ions into SiC, analyzing lattice damage, amorphous defects, and temperature distribution. H+ ion implantation resulted in a higher number of amorphous atoms compared to Cu2+ ions. The maximum atomic temperature during Cu2+ ion implantation was significantly higher (1635 K) than during H+ ion implantation (950 K), although the volume of the temperature rise region was larger in the H+ model. Cu2+ ions induced more severe lattice vibrations than H+ ions. Atom movement along regions of weak lattice binding energy was observed. The study also examined overlapping multiple ion implantations, considering ion type, initial energy, and incident angle. Cu2+ ions exhibited smaller sputtering yield, projection range, number of amorphous atoms, and energy increment compared to H+ ions. A 0° incident angle resulted in higher sputtering yield and increased amorphous structure formation due to the channeling effect, which was more pronounced in the H+ model. The experimental results demonstrate that compared to Cu2+ ions, H+ ions have a greater impact on the surface peak roughness, sub-surface damage depth, and surface damage of SiC samples. It can provide a reliable guidance for selecting process parameters and the types of ions to implant.

Modeling of Electron and Lattice Temperature Distribution Through Lifetime of Plasma Plume

When employing shorter (sub picosecond) laser pulses, in ablation kinetics the features appear which can no longer be described in the context of the conventional thermal model. Meanwhile, the ablation of materials with the aid of ultra-short (sub picosecond) laser pulses is applied for micromechanical processing. Physical mechanisms and theoretical models of laser ablation are discussed. Typical associated phenomena are qualitatively regarded and methods for studying them quantitatively are considered. Calculated results relevant to ablation kinetics for a number of substances are presented and compared with experimental data. Ultra-short laser ablation with two-temperature model was quantitatively investigated. A two-temperature model for the description of transition phenomena in a non-equilibrium electron gas and a lattice under picosecond laser irradiation is proposed. Some characteristics are hard to measure directly at all. That is why the analysis of physical mechanisms involved in the ablation process by ultra-short laser pulses has to be performed on the basis of a theoretical consideration of `indirect' experimental data. For Copper and Nickel metal targets, the two-temperature model calculations explain that the temperature of the electron subsystem increased suddenly and approached a peak value at the end of laser pulse. In addition, the temperature profile of lattice temperature subsystem evolution slowly, and still increasing after the end of laser pulse. A good agreement prevails when a comparison between the present results and published results.

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.

The impact of self-heating and its implications on hot-carrier degradation – A modeling study

A combination of hot-carrier degradation (HCD) and self-heating (SH) was acknowledged to be the most detrimental reliability issue in ultra-scaled field-effect-transistors (FETs) with confined architectures, such as fin and nanowire (NW) FETs. Although the view on whether SH accelerates or inhibits HCD in n-channel devices is controversial, it is commonly accepted that in p-channel FETs HCD becomes more pronounced due to SH. Therefore, we develop a framework for modeling coupled HCD and SH and validate it against experimental data acquired in p-channel Si NWFETs. This framework incorporates a carrier transport solver linked to a solver for the lattice heat flow equation; the latter solver allows one to evaluate a non-uniform lattice temperature distribution in the device. Carrier energy distribution functions obtained considering coordinate-dependent lattice temperature are used to calculate the rates of the multiple- and single-carrier processes of SiH bond dissociation. In addition to perturbation of carrier transport by SH, elevated lattice temperature results in enhancement of the thermal contribution to the bond rupture rate and shortens vibrational lifetime of the SiH bond, thereby reducing the multiple-carrier process rate. All these three aspects are captured by our framework, importance of each of them is analyzed, and our approach was shown to accurately reproduce experimental data.

Numerical simulation and validation of subsurface modification and crack formation induced by nanosecond-pulsed laser processing in monocrystalline silicon

We describe a numerical simulation of subsurface modification and crack formation in monocrystalline silicon induced by nanosecond-pulsed laser irradiation. In this model, we assume the residual stress generation due to material transfer caused by volume reduction during melting and resolidification to be the dominant factor in creating subsurface mechanical stress and cracks. In order to quantitatively determine the geometry of the modified region, we numerically model the nonlinear propagation and absorption of the laser beam and the thermal transport. We find that during a single pulse, the lattice temperature distribution results in melting, material transfer, and structural changes on resolidification. The residual stress generated within the monocrystal adjacent to the modified region is subsequently assessed for crack formation in the substrate. The validity of the proposed model is confirmed through agreement with a number of experimental results, including the transmitted power, the timing of the onset of the phase transition during laser irradiation, the processing threshold, the geometry of the modified region, and the formed crack length.

Characterization and Modeling of Hydrogen-Terminated MOSFETs With Single-Crystal and Polycrystalline Diamond

The mechanism of hydrogen-terminated (H-terminated) single-crystal and polycrystalline diamond metal–oxide field-effect transistors (MOSFETs) is investigated in this letter. In order to characterize the complicated p-type surface layer in H-terminated diamond MOSFETs, both p-type acceptors and the C–H dipole effect are considered in our model. Simulated hole distribution and band bending are used to illustrate the operation mechanism in the surface region. Simulated results by using the proposed model match well with both measured ${I} - {V}$ and transfer characteristics of these two kinds of diamond MOSFETs. Moreover, channel lattice temperature distribution reveals that self-heating effect-induced slight current collapse occurs in the polycrystalline diamond MOSFET at ${I}_{\text {ds}} $ over 500 mA/mm due to relatively lower thermal conductivity. Finally, the lateral electric field and hole velocity distribution under the gate electrode are given to aid future research.

Effects of dissipative substrate on the performances of enhancement mode AlInN/GaN HEMTs

AbstractAlInN/GaN high electron mobility transistors (HEMTs) exhibit numerous advantages compared to other known semiconductor devices. However, it is more difficult to realize the enhancement mode (E‐mode) HEMTs of AlInN/GaN than those of the AlGaN/GaN heterostructure, because of the higher 2‐dimensional electron gas density at the AlInN/GaN interface. In this work, using simulations, it is shown that the E‐mode can be achieved in AlInN/GaN HEMTs by tuning the thickness of the AlInN barrier layer to less than 1.14 nm in our investigated structure. Based on the E‐mode structure, the device performance stability of Al0.83In0.17N/GaN HEMTs with different heat dissipative substrates was evaluated to explore their effect on the suppression of the self‐heating behavior. The DC behavior, device temperature, lattice temperature distribution, current cutoff frequency (fT), unilateral power‐gain‐cutoff frequency (fmax), and transient response were investigated comparatively. The results indicate that the AlInN/GaN HEMTs with a free‐standing GaN substrate exhibit the best performance characteristics, ie, lowest lattice temperature, highest fT, and fastest transient response, in comparison with those using the flip‐chip substrate and sapphire substrate. Our simulation results suggest that the free‐standing GaN substrate can significantly improve the thermal stability and other basic performance characteristics of the E‐mode AlInN/GaN HEMTs.

Investigation of the Double Current Path Phenomenon in Gate-Grounded Tunnel FET

Gate-grounded tunnel field-effect transistors (ggTFETs) are considered as basic electrostatic discharge (ESD) protection devices in TFET-integrated circuits. It has been reported that two current paths exist when the ggTFET is turned on under the ESD events. In this letter, the double current path phenomenon in ggTFETs is further investigated using TCAD simulation. It is found that the upper path is a hole current path, while the lower path mainly consists of electrons, and the grounded gate is a major factor that influences the double current path phenomenon. The heat and lattice temperature distributions in ggTFETs are also discussed.

Femtosecond pulse laser irradiation of gold/chromium double-layer metal film: The role of interface boundary resistance in two-temperature model simulations

In this work, the results of computational single-shot laser pulse irradiation of gold/chromium metal film using two-temperature model are presented. The optical properties of first Au layer are studied based on critical point model and temperature-dependent reflectivity and absorption coefficient are considered in model simulations with and without the effect of ballistic motion of hot electrons. The thermal response of Au/Cr double-layer film is investigated after femtosecond laser pulse irradiation with pulse duration 30fs and 800nm laser wavelength in submelting condition by introducing the influence of thermal boundary resistance. First, the ideal interface between gold and chromium is considered and the two-temperature model results for various thicknesses of gold layer are demonstrated. Then, the time and position dependence of interface resistance is calculated based on Diffuse Mismatch Model. By including the thermal boundary resistance at interface, the electron and lattice temperature distributions and the lattice overheating from chromium side are compared with the ideal interface. The results show that, in the presence of Kapitza resistance, the chromium side lattice overheating at interface is lower than the case of zero interface boundary resistance. Moreover, the two-temperature model simulations for various snapshot times and heat flow distribution for Au/Cr double-layer structure are studied. The simulated results provide more information about femtosecond laser irradiation for double-layer metal films.

A Study on Self-Heating and Mutual Thermal Coupling in SiGe Multi-Finger HBTs

In this paper, the self-heating and mutual thermal coupling in a state-of-the-art SiGe:C multi-finger heterojunction bipolar transistor (HBT) was investigated in static dc operation conditions. Multi-finger HBT structure was created using Sentaurus structure editor with dimensions similar to the layout of SiGe:C multi-finger HBTs in ST-Microelectronics BiCMOS55 (B55) technology (f T > 300 GHz, f max > 400 GHz) as per ST’s BiCMOS55 process design kit guidelines. Three-dimensional thermal technology computer aided design (TCAD) simulations were carried out to obtain the temperature distribution in static dc operation. The lattice temperature (T Lattice) and heat flux (F Heat) distribution inside the device were studied. The impact of back-end-of-line (BEOL) layers on static thermal behavior of the state-of-the-art SiGe:C multi finger HBTs was also investigated. The temperature dependent thermal resistance of different fingers of the trench isolated SiGe multi-finger HBT was extracted without and with back-end-of-line (BEOL) effect. An electro-thermal dc compact model of self-heating and mutual thermal coupling in multi-finger HBTs was proposed and applied to compare the modeling results with the TCAD simulation results. Very good agreement was achieved between results obtained from TCAD simulation and those obtained from compact model-based simulation.

Further Study of the U-Shaped Channel SOI-LIGBT With Enhanced Current Density for High-Voltage Monolithic ICs

A high-voltage silicon-on-insulator lateral insulated-gate bipolar transistor (SOI-LIGBT) with U-shaped channels, which are composed of parallel channels and orthogonal channels for improving the current density ( $J_{C}$ ) and latch-up immunity, is proposed and studied intensively in this paper. By using the U-shaped channels, the electron injection from the emitter into the $n$ -drift region is significantly enhanced, and the current density is improved. In addition, an analytical model is proposed, and it is indicated that $J_{C}$ can be improved as $\alpha $ (the angle between the parallel channel and the orthogonal channel) increases in a certain range. The hole current density distribution in the ON-state and the lattice temperature distribution in the short-circuit state of the proposed structure are also investigated. Increasing $\alpha $ is beneficial to alleviate the holes crowding beneath the n+ emitter and suppress the temperature rise in the JFET region, which is favorable for increasing the latch-up voltage ( $V_{\textrm {LP}}$ ) and short-circuit withstand time ( $t_{\textrm {SC}}$ ). The experiments demonstrate that the U-shaped channel SOI-LIGBT fabricated with 0.5- $\mu \text{m}$ SOI technology exhibits a high current density ( $J_{C}$ ) of 305 A/cm2 at $V_{\textrm {CE}}=3$ V and $V_{\textrm {GE}}=5$ V, and a low specific ON-resistance ( $R_{{\mathrm{\scriptscriptstyle ON}}\,\cdot \,\textrm {sp}}$ ) of 0.984 $\Omega \cdot \textrm {mm}^{2}$ with breakdown voltage of 590 V. The improved latch-up voltage ( $V_{\textrm {LP}}$ ) of 560 V and the short-circuit withstand time ( $t_{\textrm {SC}}$ ) of 5.1 $\mu \text{s}$ are obtained.

Thermal influence on charge carrier transport in solar cells based on GaAs PN junctions

The electron and hole one-dimensional transport in a solar cell based on a Gallium Arsenide (GaAs) PN junction and its dependency with electron and lattice temperatures are studied here. Electrons and heat transport are treated on an equal footing, and a cell operating at high temperatures using concentrators is considered. The equations of a two-temperature hydrodynamic model are written in terms of asymptotic expansions for the dependent variables with the electron Reynolds number as a perturbation parameter. The dependency of the electron and hole densities through the junction with the temperature is analyzed solving the steady-state model at low Reynolds numbers. Lattice temperature distribution throughout the device is obtained considering the change of kinetic energy of electrons due to interactions with the lattice and heat absorbed from sunlight. In terms of performance, higher values of power output are obtained with low lattice temperature and hot energy carriers. This modeling contributes to improve the design of heat exchange devices and thermal management strategies in photovoltaic technologies.

皮秒激光烧蚀Al膜的理论分析与实验验证

In order to investigate the energy transport process in Al film irradiated by 10 ps lasers, a semi-classical two temperature model (TTM) was applied, and a 1D finite element calculation model was constructed with finite element software. Considering phase change region of material during laser ablation, reasonable expression was added to the TTM. According to the calculation, the surface lattice temperature evolutions along with time for single pulse lasers with different powers were presented. In order to investigate the surface plasma reflectivity and the heat absorption coefficient changing with lattice temperature during laser irradiation, the free-electron gas theory was applied. Moreover, the laser generated thermoelectric field and the electron drift velocity distribution map were depicted. The results verify that the thermoelectric field is the major reason for the electron drift movement, and the location of maximum velocity is changed with time. The spatial and temporal lattice temperature distribution map of Al film irradiated by 0.12 W picosecond laser was depicted. According to the calculation, the phase explosion is the reason for ablation, and it occurs during the process of laser energy deposition. The over-heated zone (OHZ) was defined, and the relationship between ablated depths and time was found. The calculated ablation depths of single pulses coincide with the experiment for 10 ps laser.

Analytical solution for laser short-pulse heating of two-dimensional solids: volumetric and surface heat source considerations

An analytical solution for lattice temperature distribution in a metallic solid subjected to laser short-pulse heating is presented. The method of similarity solution is adopted for the solution of the diffusive–ballistic energy equation. Volumetric and surface heat sources are each incorporated separately in the analysis. The material thermal response due to both heat sources during the short heating period is analyzed. It is found that a volumetric heat source resulted in smaller temperature increase in the irradiated material than a surface heat source, despite the same laser power intensity being used in both cases. This is attributed to energy transport mechanisms taking place in the solid substrate due to volumetric and surface heat sources.

New GGNMOS I/O Cell Array for Improved Electrical Overstress Robustness

A 0.18-μm 3.3 V grounded-gate NMOS (GGNMOS) I/O cell array for timing controller (TCON) application is proposed for improving electrical overstress (EOS) robustness. The improved cell array consists of 20 GGNMOS, 4 inserted well taps, 2 end-well taps and shallow trench isolation (STI). Technology computer-aided design (TCAD) simulation results show that the inserted well taps and extended drain contact gate spacing (DCGS) is effective in preventing EOS failure, e.g. local burnout. Thermodynamic models for device simulation enable us to obtain lattice temperature distributions inside the cells. The peak value of the maximum lattice temperature in the improved GGNMOS cell array is lower than that in a conventional GGNMOS cell array. The inserted well taps also improve the uniformity of turn-on of GGNMOS cells. EOS test results show the validity of the simulation results on improvement of EOS robustness of the new GGNMOS I/O cell array.

Computational study of the Seebeck coefficient of one-dimensional composite nano-structures

The Seebeck coefficient (S) of composite nano-structures is theoretically explored within a self-consistent electro-thermal transport simulation framework using the non-equilibrium Green’s function method and a heat diffusion equation. Seebeck coefficients are determined using numerical techniques that mimic experimental measurements. Simulation results show that, without energy relaxing scattering, the overall S of a composite structure is determined by the highest barrier within the device. For a diffusive, composite structure with energy relaxation due to electron-phonon scattering, however, the measured S is an average of the position-dependent values with the weighting factor being the lattice temperature gradient. The results stress the importance of self-consistent solutions of phonon heat transport and the resulting lattice temperature distribution in understanding the thermoelectric properties of a composite structure. It is also clarified that the measured S of a composite structure reflects its power generation performance rather than its cooling performance. The results suggest that the lattice thermal conductivity within the composite structure might be engineered to improve the power factor over the bulk by avoiding the conventional trade-off between S and the electrical conductivity.

표면 Texturization을 가진 Photovoltaic Device 내부의 열 분포 특성에 관한 연구

The thermal distribution of 2D and 3D p-n photovoltaic diode structures with and without surface texturing has been studied. By analysis of the numerical simulation results of the I-V characteristics and lattice temperature distributions the effect of different texturing structures on the characteristics of silicon p-n photovoltaic devices has been studied systematically. The efficiency of the device having surface texturing shows more than ~2% enhancement compared to the reference devices which did not have texturing. In addition, the effect of the density of the texturing groove has been studied and it has been confirmed that the texturing structure not only improves the light trapping but also plays an important role in the heat radiation.

Analytical solution for electron and lattice site temperatures due to laser-induced non-equilibrium energy transport in metals

The present study describes the modeling of short-pulse laser heating of gold and copper materials. The energy transport due to a laser short pulse is formulated using the electron kinetic theory approach. Electron and lattice temperature distributions inside the substrate material during the laser short pulse are formulated analytically. In the analysis, the Laplace transformation technique is used. The results obtained from the analytical solutions are compared with numerical predictions and experimental data. It is found that the results obtained from the numerical and analytical solutions for temperature distributions are in good agreement with the experimental data.

Thermal characteristics investigation of high voltage grounded gate-LDMOS under ESD stress conditions

The thermal characteristics of high voltage gg-LDMOS under ESD stress conditions are investigated in detail based on the Sentaurus process and device simulators. The total heat and lattice temperature distributions along the Si-SiO2 interface under different stress conditions are presented and the physical mechanisms are discussed in detail. The influence of structure parameters on peak lattice temperature is also discussed, which is useful for designers to optimize the parameters of LDMSO for better ESD performance.