A novel 4H-SiC Multiple Stepped SGT MOSFET (MSGT-MOSFET) is presented and investigated utilizing TCAD simulations in this paper. We have quantitatively studied the characteristics of the device through simulation modeling and physical model calculations, and comparatively analyzed the performance and application prospects of this novel device. The gate-to-drain capacitance (C_gd) and gate-to-drain charge (Q_gd) of the MSGT-MOSFET are significantly reduced in comparison with the double trench MOSFET (DT-MOSFET) and the conventional SGT MOSFET (CSGT-MOSFET), due to the reduction of the overlapping area of the split gate (SG) structure and drift region. Therefore, the obtained high frequency figure of merit (HF-FOM) defined as [R_on × C_gd] reduced by 23.9% compared with DT-MOSFET and CSGT-MOSFET. And the HF-FOM [R_on × Q_gd] for the MSGT-MOSFET significantly decreased by 71% and 50%, respectively, compared to that of the DT-MOSFET and CSGT-MOSFET. Furthermore, the switching loss is also simulated and calculated. And the total switching loss of the proposed MSGT-MOSFET realizes 42.9% and 21.7% reduction in comparison with the DT-MOSFET and CSGT-MOSFET. The overall enhanced performances suggest that the MSGT-MOSFET is an excellent choice for high frequency power electronic applications.

Humidity sensors based on flexible sensitive nanomaterials are very attractive in noncontact healthcare monitoring. However, the existing humidity sensors have some shortcomings such as limited sensitivity, narrow relative humidity (RH) range, and a complex process. Herein, we show that a tin sulphide (SnS) nanoflakes-based sensor presents high humidity sensing behaviour both in rigid and flexible substrate. The sensing mechanism based on the Schottky nature of a SnS-metal contact endows the as-fabricated sensor with a high response of 2491000% towards a wide RH range from 3% RH to 99% RH. The response and recovery time of the sensor are 6 s and 4 s, respectively. Besides, the flexible SnS nanoflakes-based humidity sensor with a polyimide substrate can be well attached to the skin and exhibits stable humidity sensing performance in the natural flat state and under bending loading. Moreover, the first-principles analysis is performed to prove the high specificity of SnS to the moisture (H₂O) in the air. Benefiting from its promising advantages, we explore some application of the SnS nanoflakes-based sensors in detection of breathing patterns and non-contact finger tips sensing behaviour. The sensor can monitor the respiration pattern of a human being accurately, and recognize the movement of the fingertip speedily. This novel humidity sensor shows great promising application in physiological and physical monitoring, portable diagnosis system, and noncontact interface localization.

In this study, the structural, electronic and optical properties of a tungsten disulfide (WS₂) hybrid with indium-gallium-zinc-oxide (IGZO) heterostructures were investigated based on density functional theory (DFT) calculations. According to the results of binding energy, charge density difference and electron localization function of heterostructures, we found that the WS₂ and IGZO monolayers were bound to each other via non-covalent interactions with large binding energy. The calculated results illustrate that the AAii stacking pattern has an indirect band gap of 1.643 eV, while AAi and AB stacking patterns have maximum direct-gaps of 1.102 eV and 1.234 eV, respectively. Under an external E-field and mechanical strain, the response of the energy gap of the WS₂/IGZO heterostructure monotonically decreased over a wide range, even with a semiconductor-metal transition. In addition, we investigated the optical properties of the heterostructure and found that it exhibits a much broad spectral responsivity (from visible light to deep UV light) and a more pronounced optical absorption than WS₂ and IGZO monolayers. Moreover, the tensile strain could weaken the photoresponse of the heterostructure to the UV light and enhance the response for the visible light; under compressive strain, the heterostructure showed a strong absorption peak in the UV light. Meanwhile, a red-shift was observed under an external strain. All these unique and tunable properties indicate that the WS₂/IGZO heterostructure is a good candidate for nanoelectronic and photoelectronic devices, such as field-effect transistors, flexible sensors, photodetectors and photonic devices.

Recently, the application of phosphorene structure analogues in gas sensors has been a hot research topic since the appearance of phosphorene. SnSe monolayer as one of them has been proved to be much more stable properties than phosphorene. Based on the density-functional theory, the interaction between gas molecules (CO, CO ₂ , O ₂ , NO, NH ₃ , SO ₂ and NO ₂ ) and SnSe monolayer are theoretically investigated by first-principles calculation. Macroscopically, gas molecules selective adsorption of SnSe monolayer is analyzed by molecular dynamics. Compared to CO, CO ₂ , O ₂ , SnSe monolayer performs stronger affinity for SO ₂ and NO ₂ , which possesses appropriate adsorption energies (−6.000 eV and −0.759 eV) and elevated charge transfers (−0.239 e and −0.328 e). SnSe monolayer chemical adsorption of NO ₂ , while physically adsorbing SO ₂ , is more suitable for the adsorption mode of SO ₂ sensors. Surprisingly, the adsorption amount of SO ₂ is 6 times that of NO ₂ . Therefore, the adsorption of SO ₂ is more likely to occur compared to other gas molecules. For a mixed environment of SO ₂ and NO ₂ , the adsorption quantity of SO ₂ is not significantly affected, while the adsorption of NO ₂ is inhibited. Therefore, the SnSe monolayer could be a promising candidate as SO ₂ sensors with high selectivity and sensitivity.

A partial carrier stored and hole path floating dummy shield trench IGBT (PCS-FD-IGBT) is proposed and investigated by simulation. Under E_off of 8mJ/cm², the V_CE(sat)) of 1200V class PCS-FD-IGBT is 1.223V, which is 11.1% and 2.2% less than CON-FD-IGBT and HP-FD-IGBT. Besides, the EMI noise of PCS-FD-IGBT is suppressed at a lower level (dV/dt is below 80kV/μs). Moreover, the PCS-FD-IGBT improves the gate drive controllability to easily adapt the larger range of system inductance.

The electronic and mechanical properties of monolayer SnP₂ are calculated by density functional theory (DFT), showing that monolayer SnP₂ is a quasi-direct semiconductor with a moderate bandgap of 1.44 eV. The phonon dispersion, the molecular dynamics and the strain energy reveal that SnP₂ is dynamically, thermally and mechanically stable. Further, the bandgap of SnP₂ sheet can be effectively adjusted by applying strain. These results open the door for future applications in catalysis and optoelectronics.

In this work, the structural, electronic and optical properties of germanene and ZnSe substrate nanocomposites have been investigated using first-principles calculations. We found that the large direct-gap ZnSe semiconductors and zero-gap germanene form a typical orbital hybridization heterostructure with a strong binding energy, which shows a moderate direct band gap of 0.503 eV in the most stable pattern. Furthermore, the heterostructure undergoes semiconductor-to-metal band gap transition when subjected to external out-of-plane electric field. We also found that applying external strain and compressing the interlayer distance are two simple ways of tuning the electronic structure. An unexpected indirect-direct band gap transition is also observed in the AAII pattern via adjusting the interlayer distance. Quite interestingly, the calculated results exhibit that the germanene/ZnSe heterobilayer structure has perfect optical absorption in the solar spectrum as well as the infrared and UV light zones, which is superior to that of the individual ZnSe substrate and germanene. The staggered interfacial gap and tunability of the energy band structure via interlayer distance and external electric field and strain thus make the germanene/ZnSe heterostructure a promising candidate for field effect transistors (FETs) and nanoelectronic applications.

A novel terahertz modulator based on graphene is proposed and designed. The device consists of a silicon ridge covered by a graphene sheet. The transmission properties of the proposed structure demonstrate that the introduction of graphene can improve the switching and filtering performance of modulators, and enhance its field confinement capability. In the case of the number of layers, a blue shift can be observed in the center wavelength with increase of graphene layers. Meanwhile, the relationship between the number of layers and the peak of reflection spectra is an inverse proportion function. In addition, we find that the center wavelength is almost unchanged with respect to the different chemical potential, thus the effective refractive indices of the cross section of light propagation direction can be well preserved. These findings will contribute to the research and development of graphene based THz waveguide modulators.

Interfacial properties of Cu/SiO₂ in semiconductor devices has been a challenging study for many years because of its difficulties in experimentally quantifying the critical strength of interface. In this paper, a multi-scale modeling approach is built to characterize the interfacial properties between Cu and SiO₂. The Cu and SiO₂ are bonded by three types of chemical bonds, which cause three atomistic interfacial structures. The fracture of Cu-O and Cu-Si bonded interfaces occur at the interface, however, the fracture for Cu-OO interface occurs at copper layer near the interface, indicating two different fracture criterions coexist in Cu/SiO₂ system.

A systematic study of discrete SiC MOSFETs' reliability under High Temperature stress has been carried out. High Temperature stress is performed in this work to characterize the threshold voltage instability. To investigate the degradation mechanism of devices, simulation according to the structure of MOSFET cell has been performed. The result shows that the threshold voltages change trends of both MOSFETs are the same, including drop-down period at very early time due to a decrease of doping concentration at channel region and gradual raise-up period at in the rest of time resulting from decline of interface charge.

Predictive calculations based on density functional theory (DFT) are used here to study the electronic and optical properties of GeSe monolayer after adsorbing gas molecules (O₂, NH₃, SO₂, H₂, CO₂, H₂S, NO₂, CH₄, H₂O, NO, CO). Our results reveal that for all the gas molecules considered, only NH₃ is adsorbed on GeSe monolayer by physisorption. Whereas SO₂ and NO₂ are chemisorbed on GeSe monolayer with strong adsorption energies. In addition, the adsorption of O₂, NO and NO₂ distinctly enhances the optical absorbance and broaden the absorbance range of GeSe monolayer in visible light region. Also, it is found that the adsorption of H₂S, NO and NH₃ can reduce the work function of the GeSe monolayer. The results indicate that GeSe monolayer is not only a promising candidate for the sensing, capture, and storage of NH₃, but also an anticipated disposable gas sensor or metal-free catalyst for detecting and catalyzing SO₂ and NO₂. Furthermore, it has excellent potential to be applied to optical sensors, solar cells, nanoelectronics or optoelectronics devices.

Interfacial properties of Cu/SiO2 in semiconductor devices has continued to be the subject of challenging study for many years because of its difficulties in experimentally quantifying the critical strength of interface. In this paper, a multi-scale modeling approach is built to characterize the interfacial properties between Cu and SiO2. In this system, the Cu and SiO2 are bonded together by three types of chemical bonds, Cu-OO, Cu-O, and Cu-Si, which cause three atomistic interfacial structures. For Cu-O and Cu-Si bonded interfaces, the fracture occurs exactly at the interface, however, the fracture for Cu-OO bonded interface occurs at copper layer near the interface, which indicate two different fracture criterions coexist in Cu/SiO2 system. And, the calculated interfacial strength at macroscale is in agreement with available experimental results.

The color coordinate shift of light-emitting diode (LED) lamps is investigated by running three stress-loaded testing methods, namely step-up stress accelerated degradation testing, step-down stress accelerated degradation testing, and constant stress accelerated degradation testing. A power model is proposed as the statistical model of the color shift (CS) process of LED products. Consequently, a CS mechanism constant is obtained for detecting the consistency of CS mechanisms among various stress-loaded conditions. A statistical procedure with the proposed power model is then derived for the CS paths of LED lamps in step-loaded stress testing. Two types of commercial LED lamps with different capabilities of heat dissipation (CHDs) are investigated. Results show that the color coordinates of lamps are easily modified in various stress-loaded conditions, and different CHDs of lamps may play a crucial role in the various CS processes. Furthermore, the proposed statistic power model is adequate for the CS process of LED lamps. The consistency of CS mechanisms in step-loaded stress testing can also be detected effectively by applying the proposed statistic procedure with the power model. Moreover, the constant assumption in the model is useful for judging the consistency of CS mechanisms under various stress-loaded conditions.

Heat transfer across thermal interface material, such as graphene-polymer composite, is a critical issue for microelectronics thermal management. To improve its thermal performance, we use chemical functionalization on the graphene with hydrocarbon chains in this work. Molecular dynamics simulations are used to identify the thermal conductivity of monolayer graphene and graphene-polymer nanocomposites with and without grafted hydrocarbon chain. The influence of functionalization with hydrocarbon chains on the interfacial thermal conductance of graphene-polyethylene nanocomposites was investigated using a non-equilibrium molecular dynamics (NEMD) simulation. We also study the effects of the graft density (number of hydrocarbon chain) on the thermal conductivity of graphene and the nanocomposite.