High-power Devices Research Articles

Review of Nanosecond Pulse Generator With High-Power Switching Devices

Review of Nanosecond Pulse Generator With High-Power Switching Devices

Construction of rGO-MXene@FeNi/epoxy composites with regular honeycomb structures for high-efficiency electromagnetic interference shielding

With the rapid development of 5G communication technology and wearable electronic devices, the demand for low-reflection electromagnetic interference (EMI) shielding materials is becoming increasingly urgent. In this work, reduced graphene oxide-MXene (rGMH) @FeNi/epoxy EMI shielding composites with a regular honeycomb structure were successfully prepared by the combination of surface functionalization modification, sacrificial template, and freeze-drying. The effects of magnetic FeNi alloy particle loading mode and loading amount on the EMI shielding performance of composites were investigated. The results show that rGMH@FeNi/epoxy EMI shielding composites have the highest EMI shielding effectiveness (EMI SE) and the lowest reflection shielding effectiveness when magnetic FeNi alloy particles are loaded only on the graphene skeleton. In this composite, the EMI SE value of the composite is 61 dB when the rGMH@FeNi mass fraction is 5.4 wt% (f-FeNi mass fraction is 0.9 wt%), which is 4.7 times that of the blended rGO/MXene/FeNi/ epoxy resin composite (13 dB) with the same mass fraction. At the same time, the rGMH@FeNi/epoxy composite has excellent thermal stability (heat-resistance index of 190.3 °C) and mechanical properties (energy storage modulus of 8606.7 MPa). These polymer-based EMI shielding composites with excellent EMI shielding properties and low reflection effectiveness have great potential in the protection of high-power, portable and wearable electronic devices against electromagnetic pollution.

Numerical analysis of free convection under the influence of radiation and inclined MHD in a triangular cavity filled with hybrid nanofluid and a porous fin

This study presents a novel investigation into the thermal behavior of a hybrid nanofluid (MgO − Ag − H2O) in natural convection around a porous fin in a triangular enclosure under the influence of radiation and magnetohydrodynamic effects. The research uniquely combines these complex phenomena, addressing a significant gap in the literature. This configuration has potential applications in advanced solar thermal collectors, electronic cooling systems for high-power devices, and compact heat exchangers in various industries. The main objectives are to understand how various parameters influence heat transfer and fluid flow behavior and to optimize the design for enhanced thermal performance. The study considers a range of variables including Rayleigh number (103 − − 106), Hartmann number (0 – 50), Aspect ratio (0.3 – 0.6), radiation parameters (Rd = 1 − − 5, λ = 1 − 5), and volume concentration (0- 0.05), which have been numerically analyzed using the finite element method (FEM). The findings reveal that increasing the Darcy number (Da) enhances heat transfer at low Rayleigh numbers (Ra = 103,104). However, at higher Ra (Ra = 106), the impact of Da becomes more complex, with a critical Da beyond which heat transfer efficiency decreases due to an increase in flow resistance. The nanoparticle volume concentration plays a vital role, as higher concentrations lead to improved heat transfer efficiency, especially at higher Ra, through enhanced thermal conductivity and thermal dispersion. The length of the porous fin greatly impacts fluid flow patterns and heat transfer rates, with longer fins creating more complex flow patterns, promoting enhanced heat transfer and stronger thermal plumes. Thermal radiation, represented by the radiation parameters (Rd and λ), significantly influences both the heat transfer rate and the convective flow patterns within the enclosure. This study also incorporates a comprehensive entropy generation analysis, providing novel insights into system irreversibilities and optimization potential. The entropy analysis reveals the complex interplay between various parameters and their impact on system efficiency, offering valuable guidance for designing high-performance thermal management systems.

Highly porous activated carbon derived from plant raw material as high-performance anode for aqueous sodium-ion supercapacitors

High power sodium energy generation devices, such as symmetric and hybrid supercapacitors, have great potential for cheap and green post-lithium applications. However, it is imperative to obtain porous structures with large surfaces and optimized pore size to enhance the electrode sorption property and to ensure fast electrochemical reactions. In this work, we investigated the influence of KOH carbon activation conditions on the morphology, porosity, and electrochemical parameters in aqueous sodium electrolytes. Our activated carbon had a maximum surface area of 1556 m2/g and a notably high mesopore content, this varying from 5 to 19 % of the total pore area. Electrochemical parameters are not only influenced by the total number of pores, but also by the optimal ratio of meso and micro pores. It is shown that in the case of sodium-based electrolytes, mesopores provide good electrode-electrolyte contact, and the capacity is mainly provided by micropores. High operating values of activated carbon in sodium aqueous electrolytes (specific capacity about 78 F/g, energy density 11 W*h/kg and power density 470 W/kg) indicates that the optimal electrode materials for a high-power device are activated carbon with a high content of mesopores obtained by the ratio of C and KOH as 1:4.

Experimental study of dielectric liquid spray cooling on multi-scale structured surfaces inspired by leaf veins

Dielectric liquid spray cooling is a promising way to dissipate heat of high-power electronic devices. Surface modification is a most cost-effective method to enhance spray cooling. Inspired by leaf veins, this paper designs and fabricates macro-scale, micro- and nano- scale, and multi-scale structured surfaces for dielectric liquid spray cooling. The cooling characteristics are tested on a two-phase spray cooling system using HFE-7100. The results reveal that the heat transfer is enhanced on all the structured surfaces. Two bionic leaf vein structures, reticulated veins and parallel veins, are designed for macro-scale structured surfaces. The results show that the former one is superior to the other thanks to its better liquid distribution. For the micro- and nano- scale structured surfaces, due to the larger surface area and higher thermal conductivity, the graphene coating outperforms the carbon nanotube coating in heat transfer. Multi-scale structured surfaces, featured with leaf veins and micro- and nano- coatings, further enhance heat transfer. The heat flux increases by 116 % compared with that of the smooth surface. The evaporation efficiency reaches 60 % at the surface temperature of 80 °C. Furthermore, the effect of surface temperature on the enhancement ratio of heat transfer is analyzed, revealing various enhancement mechanisms of different scaled structured surfaces.

Strong pinning effect on domains in piezoelectrics

In high-power applications, since mechanical losses in piezoelectric devices always result in considerable heat generation, the temperature stability of the mechanical quality factor (Qm) is particularly crucial and should be considered in real piezoelectric applications. Here, we propose a poling-aging-repoling strategy to make the defect dipoles aligned with the poling direction as much as possible, thereby resulting in the strong pinning of ferroelectric domains. A giant internal bias field Ei (11.6 kV cm−1 @ 1 Hz) and a high Qm (2074), accompanied by almost unchanged d33, are obtained in the composition of CuO-doped (K0.48Na0.52)0.94Li0.06Nb0.94Ta0.06O3 (KNNLT-Cu) ceramics with a diffused polymorphic phase transition. Furthermore, and this is more encouraging, the high electromechanical performance exhibits good temperature stability in the range from room temperature to 100 °C, suggesting that the thermal stability of Qm can be effectively improved by combining the strong pinning of defect dipoles with composition design and providing a way for the development and design of future high-power piezoelectric devices.

Gate mesa terminal with drain-field-plated β-Ga2O3 MOSFET with ultra-high power figure of merit

In this article, a novel gate mesa terminal (GMT) device structure incorporating a drain field plate is proposed. This design features mesa terminals with varying bevel angles positioned atop the gate. The objective is to enhance the breakdown voltage (Vbr) and reduce the on-resistance (Ron) of the lateral β-Ga2O3 metal-oxide-semiconductor field-effect transistor (MOSFET). Through the implementation of the GMT structure, the peak electric field within the β-Ga2O3 MOSFET is redirected towards the passivation layer. This effectively mitigates the electric field in the epitaxial layer, thereby increasing Vbr. The optimal values for Vbr, specific on-resistance (Ron,sp) and maximum transconductance (gm) across various GMT structures are 4827 V, 9.9 mΩ·cm2 and 15.32 mS/mm, respectively. These metrics represent a 2.63-fold, 0.88-fold, and 1.25-fold improvement compared to the non-GMT structure. Additionally, when the doping concentration of epitaxial layer is 1 × 1016 cm−3, the GMT achieves an enhanced threshold voltage of +0.26 V. By simulating different bevel angles, field plate parameters, epitaxial layer doping concentrations, and mesa thicknesses, an optimal power figure of merit (PFOM) of 1.914 GW cm−2 is attained. This innovative design introduces a fresh concept for the development of the next generation of high voltage and high-power devices rated above 4 KV.

Research on the division of heat dissipation spaces for multiple heat sources based on the adiabatic characteristic of heat flow lines

Due to the pressing need for compact layouts, the spacing between high-power devices is gradually decreasing, making the mutual influence between multiple heat sources unavoidable. Therefore, this paper proposes a method based on the adiabatic characteristics of heat flow lines and their convergence positions to evaluate the rationality of the thermal space design of each heat source. This method has been validated for applicability in one-dimensional, two-dimensional, and three-dimensional multi-heat-source conjugate convection heat transfer. Heat flow lines have significant advantages in describing energy flow, as they align with the direction of the temperature gradient. In thermal spaces with adiabatic boundaries or mutual influences between multiple heat sources, heat flow lines converge at certain positions. The relationship between adiabatic boundaries and heat flow line convergence positions has been studied, and a more interpretative decoupling scheme for multi-heat-source systems has been proposed. The main feature of this scheme is the separation of each heat source in the same steady-state thermal space and assigning adiabatic boundaries to the solid partition surfaces, allowing efficient observation of the thermal conditions of individual heat sources and targeted layout optimization. Results indicate that this method can utilize changes in heat flow line convergence positions to assess current thermal conditions and can be used to compare the thermal performance of different shaped heat sinks. Simulation results show that under the same mass conditions, thin-fin heat sinks perform 47 % better than thick-fin heat sinks, providing a more comprehensive and intuitive assessment compared to metrics such as thermal resistance and average temperature. The proposed method offers new ideas for multi-heat-source layout optimization, heat flow control, multi-heat-source partitioned simulation, and abnormal heating detection in multiple heat sources.

The role of polymer gel electrolyte infiltration for enhancement of capacitance and cycle stability

With the increasing application of electronic materials in various fields such as flexible electronic textiles, wearable and portable gadgets, aerospace and aircraft systems etc., the demand for clean high-power energy storage devices is also increasing rapidly. To date, the application of market available supercapacitors has not met the energy expectations in the range of market leading Li-ion batteries (LIBs) due to their unreliable mechanical flexibility, electrolyte leakage, low voltage application, low capacity, low cycle stability and moderate rate-capability. Inappropriate utilization of the maximum porosity of the electrode material and inefficient activities of the electrode/electrolyte interface are major challenges for present supercapacitor development. In this work, for the first time, the role of polymer gel electrolyte infiltration to improve the electrochemical performance of a supercapacitor has been explicitly studied and investigated. It has been observed that 1-Ethyl-3- Methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI] ionic liquid electrolyte embedded in Polypropylene Carbonate (PPC) and Polycarbonate (PC) polymer matrix polymer gel electrolyte (PGE) showed excellent supercapacitive performance at high voltage window 2.6 V by delivering maximum total capacitance of 5.81 F and maximum energy density 10.9 Wh kg-1 at 30 mA current (0.06 A g-1). Regular infiltration of the polymer gel electrolyte inside the electrode material is also observed during long cycle operation of 10,000 cycles. Infiltration of electrolyte ions into the pores of electrode materials plays a significant role in increasing capacitance and cycle Stability. These results highlight the potential of this novel high-voltage polymer gel electrolyte for future high-power energy storage device applications.

Printable thermal interface materials with excellent heat dissipation capability

The rapid progression of electronic devices underscores the need for thermal interface materials (TIMs) with superior heat dissipation capabilities to address the overheating issues of high-power density electronic devices. However, the importance of excellent printability in practical automated production for TIMs has often been overlooked. This study introduces poly(2-[[(butylamino)carbonyl]oxy]ethyl acrylate)/liquid metal (Poly (BCOE)/LM) composites, which exhibit excellent printability and heat dissipation properties. The resulting materials, containing 80 wt% LM, display a low total thermal resistance of 0.69 cm2 kW−1, a low contact thermal resistance of 0.25 cm2 kW−1, a high thermal conductivity of 3.49 W m−1K−1, and effective printing capabilities through material jetting 3D printing onto chip surfaces. In thermal management applications, the composite material prepared in this work was able to reduce the temperature of the chip by a further 17 °C compared to a commercial product (Laird TFlex 300), thus highlighting its practical utility in automated production processes. This novel TIM offers a viable solution for addressing the thermal management needs of modern electronic devices.

(Invited) Ga2O3 Semiconductor Devices for High-Temperature Operation

Beta phase of gallium oxide (Ga2O3) has attracted a lot of attention as an ultra-wide band gap semiconductor for applications in high-power electronic devices. High power operation often comes with increased temperatures of the devices due to joule heating, especially in semiconductors like Ga2O3with low thermal conductivity. However, electrical performance and reliability of the Ga2O3based diodes and transistors at very high temperature, above 400C, is not well established.In this talk, I will present our recent experimental results on fabrication of Ga2O3semiconductor devices for applications as high-temperature diodes and hydrogen gas sensors. The fabricated Ga2O3/NiO p-n heterojunctions allow for device operation with >100-1000 rectification ratio up to 400-600C [1]. Despite the stable ultrathin Ohmic contact [2], the device performance degrades over tens of temperature cycles and hundreds of hours at these elevated temperatures, likely due to instability of the rectifying contact. We propose and implement alternative interfacial rectifying contact layers, that enable both high performance and long reliability of these high temperature Ga2O3 semiconductor devices.[1] Sohel, Zakutayev et al Physica Status Solidi (a) 220 2300535 (2023)[2] Callahan, Zakutayev et al J. Vac. Sci. Technol. A 41, 043211 (2023)

Mechanical–thermal coupling in micro-nanocavity graphene/paraffin phase change energy storage materials for heat management

Combining the superior thermal conductivity of graphene and the outstanding heat storage of paraffin, micro-nanocavity graphene/paraffin nanocomposites (MNGPNs) have recently served as promising thermal management materials in high-power microelectronic devices. However, current evaluations of the thermal management performances of MNGPNs are restricted in the lab condition, deviating from the complex mechanical–thermal coupling environment in practical scenarios. Here, we have investigated the structural and thermal management properties of MNGPNs with varying mechanical loads by in situ electron microscopy and in situ thermal characterizations. Our results reveal distinct mechanical–thermal coupling effects along in-plane and out-of-plane directions of MNGPNs. Specifically, mechanical loading reduces the porosity and enhances the heat transfer capacity of MNGPNs in the out-of-plane direction, while mechanical loading along the in-plane direction causes local damage to the graphene structure and weakens the heat transfer capacity of MNGPNs. Since the heat management performance of MNGPNs is dominated by the in-plane thermal transport, MNGPNs with mechanical loading show a delayed phase transition response time and unchanged phase transition enthalpy. This work provides in situ mechanical guidance for the practical application of MNGPNs for heat management.

Development and numerical optimization of a cylindrical wire-fin-type integrated ionic wind heat sink for cooling high-power LEDs

Light-emitting diodes (LEDs) are becoming increasingly high-power and compact, which makes rotary fans incompetent in some cooling situations. The ionic wind technique can compensate for the shortcomings of rotating fans, owing to its benefits of no moving parts and compact structure. Integrating the ionic wind generator with heat dissipation fins can effectively reduce the size of LED devices, but research in this area is still insufficient. In this study, an integrated ionic wind heat sink is designed for cooling LEDs. The multi-physical characteristics of discharge, flow, and heat transfer are numerically studied. The geometric parameters’ impact degree and mechanism on the multi-physical characteristics are analyzed. The performance optimization of the integrated heat sink is realized and verified. The fin length, flow channel center angle, and relative position of the fin have a large influence on the average velocity of ionic wind. The relative position of the wire electrode determines the electric field strength distribution, and it has the greatest influence on the ionic wind performance. The emitting electrode being placed at the inlet edge of the collecting electrode produces a high ionic wind flow rate. The integrated ionic wind heat sink designed in this study exhibits an outstanding cooling performance and temperature uniformity. This device can cool down the surface of a heat source with a power of 200 W to below 91 °C and make the average heat transfer coefficient reach 18.6 W/(m2·K). This study proposes a valuable method to optimize the integrated ionic wind heat sink for cooling high-power electronic devices.

Exploring the process-microstructure-thermal properties relationship of resin-reinforced Ag sintering material for high-power applications via 3D FIB-SEM nanotomography

Resin-reinforced Ag sintering materials represent a promising solution for die-attach applications in high-power devices requiring enhanced reliability and heat dissipation. However, the presence of resin and intricate microstructure poses challenges to its thermal performance, and improvement strategies remain unclear. This work utilizes 3D FIB-SEM nanotomography to reconstruct the microstructure of this material under various process conditions. The analysis reveals that, even with an Ag volume fraction as low as 47.3%, Ag particles form a robust 3D network. Geometric tortuosity quantifies the effect of different sintering conditions on the Ag particle network in all spatial directions. Effective thermal conductivity is simulated based on realistic microstructure models. Results show a significant negative correlation between tortuosity and effective thermal conductivity. Increasing sintering temperature in Model B notably reduces tortuosity and enhances effective thermal conductivity. Sensitivity analysis underscores the dominant role of Ag volume fraction in regulating effective thermal conductivity. Finally, transient thermal impedance measurement of this material as a thin die-attach layer in actual high-power devices demonstrated its application potential. This article strives to explore the relationship between process, microstructure, and thermal properties of this material to provide a reference for further development.

Green endoscopy, one step toward a sustainable future: Literature review.

Rapid climate change or climate crisis is one of the most serious emergencies of the 21st century, accounting for highly impactful and irreversible changes worldwide. Climate crisis can also affect the epidemiology and disease burden of gastrointestinal diseases because they have a connection with environmental factors and nutrition. Gastrointestinal endoscopy is a highly intensive procedure with a significant contribution to greenhouse gas (GHG) emissions. Moreover, endoscopy is the third highest generator of waste in healthcare facilities with significant contributions to carbon footprint. The main sources of direct carbon emission in endoscopy are use of high-powered consumption devices (e.g. computers, anesthesia machines, wash machines for reprocessing, scope processors, and lighting) and waste production derived mainly from use of disposable devices. Indirect sources of emissions are those derived from heating and cooling of facilities, processing of histological samples, and transportation of patients and materials. Consequently, sustainable endoscopy and climate change have been the focus of discussions between endoscopy providers and professional societies with the aim of taking action to reduce environmental impact. The term "green endoscopy" refers to the practice of gastroenterology that aims to raise awareness, assess, and reduce endoscopy´s environmental impact. Nevertheless, while awareness has been growing, guidance about practical interventions to reduce the carbon footprint of gastrointestinal endoscopy are lacking. This review aims to summarize current data regarding the impact of endoscopy on GHG emissions and possible strategies to mitigate this phenomenon. Further, we aim to promote the evolution of a more sustainable "green endoscopy".

Enhancing photoluminescence of monolayer MoS2 on h-BN substrate through plasmonic resonance for high-power optoelectronic devices

Abstract Hexagonal boron nitride (h-BN) is an excellent substrate material due to its superb thermal conductivity, excellent thermal stability and smooth surface qualities. In this study, a silicon-based h-BN substrate was prepared using the magnetron sputtering technique. Subsequently, monolayer MoS2 obtained by the CVD method was transferred onto the h-BN substrate. Then, Au-core-Ag-shell nanoparticles with a diameter of 80 nm were prepared by a self-assembly method and uniformly dispersed and spin-coated on the MoS2 surface. Applying a laser with a wavelength of 532 nm can effectively excite the plasma resonance effect of the system. Under the intense thermal effect induced by the high laser power and plasma effect, the h-BN substrate ensures that MoS2 exhibits less red-shift and higher photoluminescence intensity compared with SiO2 substrate due to its excellent thermal conductivity. This means that h-BN substrates are particularly suitable for optoelectronic applications under high laser power environments, and can maintain excellent optoelectronic device performance while effectively curbing overheating to ensure long-term stable device operation.

Effect of substrates on the structural, surface chemical state, and optical properties of Ga-doped Al2O3 thin films

We report the stabilization of Ga-doped Al2O3 (GaAlO) thin films into rhombohedral structure (R 3‾ c space group). We used the target material of composition A11.5Ga0.5O3 (bulk) to deposit the films on Alumina (0001) and p-type Si (100) substrates by using the electron beam evaporation technique. X-ray diffraction pattern confirmed the formation of polycrystalline rhombohedral structure for the as-grown films on Alumina substrate, whereas the films grown on Si substrate showed amorphous structure. The post-heat treatment of as-grown films at 550 °C stabilized rhombohedral structure in all the films, irrespective of the substrates. X-ray photoelectron spectra confirmed modification in surface chemical state of the films depending on nature of the substrates. Optical bandgap of the GaAlO films was stabilized in the range of 3.44 eV–4.04 eV, which is substantially reduced in comparison to corundum structured α-Al2O3 having optical band gap in the range of 8–9 eV and α-Ga2O3 having optical band gap of 4.5–5.5 eV. The defect-induced electronic states and substrate induced interfacial diffusion contributed additional energy gap in the range of 1.50–2.92 eV for GaAlO films grown on Si substrate. The development of highly crystalline corundum structured α-(Al, Ga)2O3 alloyed thin films and engineering their band gap energy in a wide range (1.5–4 eV) is useful for applications of semiconductor metal oxides in high power and medium frequency opto-electronic devices.

Numerical analysis of fluid flow and heat transfer characteristics in single crystal diamond microchannels with ribs and secondary channels

To meet the heat dissipation requirements of high-frequency and high-power electronic devices, single crystal diamond microchannels (SCD-MC) with secondary channels and rib combinations are proposed. The fluid flow and heat transfer characteristics in SCD-MC with various secondary channels and rectangular rib combinations are investigated through numerical simulations. The comprehensive performance and energy saving effect of the microchannel were evaluated by analyzing the factor of merit and entropy generation performance. The results show that the SCD-MC with secondary channels and rib combinations enhance fluid disturbance and increase the solid–liquid contact area, significantly improving heat transfer. When Reynolds number (Re) is 586, compared with the straight microchannel, the average temperature at the bottom of the SCD-MC with rectangular secondary channels and rectangular rib (Case 5) is reduced by 4.8 K, the heat transfer coefficient is increased by 209.8 %, and the factor of merit is improved by 89.2 %. The entropy generation augmentation number of the Case 5 microchannel was the minimum of 0.52, which has the highest energy saving effect. The factor of merit of the Case 5 microchannel exhibits a tendency to first increase and then decrease with the increase of the relative width of the secondary channel (Ψ), the relative width of the rib (Φ), and the relative position of the rib (Π). At Re = 586, Ψ = 0.933, Φ = 0.667, and Π = 0.5, the factor of merit of the Case 5 microchannel is 2.08, indicating the highest comprehensive performance. This finding provides new ideas and methods for the design and application of microchannel thermal management.

Linear stability analysis of micropolar nanofluid flow across the accelerated surface with inclined magnetic field

PurposeThe purpose of this paper is to study the two-dimensional micropolar fluid flow with conjugate heat transfer and mass transpiration. The considered nanofluid has graphene nanoparticles.Design/methodology/approachGoverning nonlinear partial differential equations are converted to nonlinear ordinary differential equations by similarity transformation. Then, to analyze the flow, the authors derive the dual solutions to the flow problem. Biot number and radiation effect are included in the energy equation. The momentum equation was solved by using boundary conditions, and the temperature equation solved by using hypergeometric series solutions. Nusselt numbers and skin friction coefficients are calculated as functions of the Reynolds number. Further, the problem is governed by other parameters, namely, the magnetic parameter, radiation parameter, Prandtl number and mass transpiration. Graphene nanofluids have shown promising thermal conductivity enhancements due to the high thermal conductivity of graphene and have a wide range of applications affecting the thermal boundary layer and serve as coolants and thermal management systems in electronics or as heat transfer fluids in various industrial processes.FindingsResults show that increasing the magnetic field decreases the momentum and increases thermal radiation. The heat source/sink parameter increases the thermal boundary layer. Increasing the volume fraction decreases the velocity profile and increases the temperature. Increasing the Eringen parameter increases the momentum of the fluid flow. Applications are found in the extrusion of polymer sheets, films and sheets, the manufacturing of plastic wires, the fabrication of fibers and the growth of crystals, among others. Heat sources/sinks are commonly used in electronic devices to transfer the heat generated by high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes to a fluid medium, thermal radiation on the fluid flow used in spectroscopy to study the properties of materials and also used in thermal imaging to capture and display the infrared radiation emitted by objects.Originality/valueMicropolar fluid flow across stretching/shrinking surfaces is examined. Biot number and radiation effects are included in the energy equation. An increase in the volume fraction decreases the momentum boundary layer thickness. Nusselt numbers and skin friction coefficients are presented versus Reynolds numbers. A dual solution is obtained for a shrinking surface.

Towards first-principles predict of doped α-Ga2O3 based structural and electrical properties

The α-Ga2O3 holds significant research value on high power device applications for its superior breakdown voltage performance. However, research concerning the doping of α-Ga2O3 remains scant, and the optimal dopant remains unidentified. To identify a potential n-type dopant, a theoretical study of the effects of group IV atoms (Si, Ge, Sn) on doped α-Ga2O3 was evaluated through the first principles calculations. We have systematically explored the lattice deformation, band structure, density of state, charge density difference and electron localization functions. The electron mobility is then evaluated by the deformation potential theory. The lowest formation energy of the Si-doped system suggests it forms the most readily. Meanwhile, Si loses approximately 1.5 times more electrons than Ge and Sn in the doped α-Ga2O3, as evidenced by the charge density difference and electron localization functions. Furthermore, our results reveal that Si is a superior dopant over Ge and Sn. It is owing to a small interaction between the Si 3 s state and the Ga 4 s generated host CBM, resulting in a minimal effect on the CBM even at high doping levels. The findings of this study have important consequences for improving the doping process of α-Ga2O3 and achieving the development of optoelectronic devices.