Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

A large amount of work world-wide has been directed towards obtaining an understanding of the fundamental characteristics of porous Si. Much progress has been made following the demonstration in 1990 that highly porous material could emit very efficient visible photoluminescence at room temperature. Since that time, all features of the structural, optical and electronic properties of the material have been subjected to in-depth scrutiny. It is the purpose of the present review to survey the work which has been carried out and to detail the level of understanding which has been attained. The key importance of crystalline Si nanostructures in determining the behaviour of porous Si is highlighted. The fabrication of solid-state electroluminescent devices is a prominent goal of many studies and the impressive progress in this area is described.

The structural and luminescence properties of porous silicon

The role of extended and point defects, and key impurities such as C, O, and H, on the electrical and optical properties of GaN is reviewed. Recent progress in the development of high reliability contacts, thermal processing, dry and wet etching techniques, implantation doping and isolation, and gate insulator technology is detailed. Finally, the performance of GaN-based electronic and photonic devices such as field effect transistors, UV detectors, laser diodes, and light-emitting diodes is covered, along with the influence of process-induced or grown-in defects and impurities on the device physics.

Gan : processing, defects, and devices

We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Industries such as the automotive, aerospace or military, as well as environmental and biological research have promoted the development of ultraviolet (UV) photodetectors capable of operating at high temperatures and in hostile environments. UV-enhanced Si photodiodes are hence giving way to a new generation of UV detectors fabricated from wide-bandgap semiconductors, such as SiC, diamond, III-nitrides, ZnS, ZnO, or ZnSe. This paper provides a general review of latest progresses in wide-bandgap semiconductor photodetectors.

https://iopscience.iop.org/article/10.1088/0268-1242/18/4/201/pdf

Wide-bandgap semiconductor ultraviolet photodetectors


 The suppression and compensation effect of oxygen on heavily boron doping behaviors and characteristics in microwave plasma chemical vapor deposition (MPCVD) diamond films are investigated. The suppression on boron incorporation is observed with crystal quality improved when oxygen added into diamond doping process. A relatively low hole concentration is expected and verified by the Hall effects measurements due to the compensation effect of oxygen as a deep donor in diamond. Low acceptor concentration, high compensation donor concentration, and relatively larger acceptor ionization energy are then induced by oxygen addition, however, heavily boron-doped diamond film with high crystal quality can also be expected. The formation of oxygen-boron complex structure instead of oxygen substitution as indicated by X-ray photoelectron spectroscopy (XPS) results is suggested to be more responsible for the observed enhanced compensation effect due to its predicted low formation energy. Meanwhile, density functional theory (DFT) calculations show that the B-O complex structure are easily formed in diamond with a formation energy of -0.83 eV. This work provides a comprehensive understanding on the compensation of oxygen on the heavily boron-doped diamond.

Suppression and compensation effect of oxygen on heavily boron doping behavior in diamond films

The present invention provides a method for removing burrs of battery electrode plates using inductively coupled plasma (ICP) dry etching, in which an induction coil is used for ionizing reaction gas. A DC bias is applied to accelerate the ionized reaction gas to bombard the burrs of electrode plate, removing burrs that formed in machining processes using physical bombardment. The equipment used in the present invention is an ICP etch system. The method according to the present invention can completely remove the burrs of electrode plate, thereby effectively preventing short circuits caused by burrs penetrating the membrane separator in the battery.

Method for removing burrs of battery electrode plates by inductively coupled plasma dry etching

In this paper, SiNx film deposited by plasma-enhanced chemical vapor deposition was employed as a gate dielectric of AlGaN/GaN high electron mobility transistors (HEMTs). We found that the NH3 flow during the deposition of SiNx can significantly affect the performances of metal–insulator–semiconductor (MIS) HEMTs. Compared to that without using NH3 flow, the device with the optimized NH3 flow exhibited three orders of magnitude lower gate leakage current, two orders of magnitude higher ON/OF drain current ratio, and an increased breakdown field by 69%. In addition, an in situ N2 plasma surface treatment prepared prior to SiNx deposition can further improve DC performances of MIS-HEMTs to a very low gate leakage current of 10−9 mA/mm and a high ON/OFF drain current ratio up to 109 by reducing the interface state density. These results demonstrate the great potential for using PECVD-SiNx as a gate dielectric in GaN-based MIS-HEMTs.

https://www.mdpi.com/2072-666X/13/9/1396/pdf?version=1661512264

Low Leakage Current and High Breakdown Field AlGaN/GaN MIS-HEMTs Using PECVD-SiNx as a Gate Dielectric

SiH4 and GeH4 Deposition and In-Situ Doping of SiGe/Si Strained Heterostructures by Rapid Thermal Process Very Low Pressure Chemical Vapor Deposition method have been studied in this paper. Ge incorporation rate increases to a maximum value and then decreases as temperature increases, the growth rate of SiGe alloy reaches its maximum value and then decreases as Ge composition increases. Ge incorporation also enhances Si deposition rate in SiGe alloy. The Boron and Phosphorus doping would change thegrowth rate of SiGe layers and the sharp doping interfaces in SiGe/Si heterostructures have been obtained.

The Growth and In-Situ Doping of SiGe/Si Strained Heterostructures by RTP/VLP-CVD

We report radio-frequency (RF) MOSFETs with a two-dimensional-electron-gas-like (2DEG-like) channel formed at the <inline-formula> <tex-math notation="LaTeX">$\beta $ </tex-math></inline-formula>-Ga2O3 surface through the low-energy implantation of Si and rapid thermal activation process. The shallowly implanted channel exhibits a strong electron confinement near surface with a high sheet concentration of <inline-formula> <tex-math notation="LaTeX">${3}.{2}\times {10} ^{{13}}$ </tex-math></inline-formula> cm−3. With the high scaling of gate length (<inline-formula> <tex-math notation="LaTeX">${L}_{\text {G}}{)}$ </tex-math></inline-formula>, the current cut-off frequency (<inline-formula> <tex-math notation="LaTeX">${f}_{\text {T}}{)}$ </tex-math></inline-formula> and maximum oscillation frequency (<inline-formula> <tex-math notation="LaTeX">${f}_{\text {max}}{)}$ </tex-math></inline-formula> were inversely proportional to <inline-formula> <tex-math notation="LaTeX">${L}_{\text {G}}$ </tex-math></inline-formula> along with a high electron saturation velocity of <inline-formula> <tex-math notation="LaTeX">${2}.{7}\times {10} ^{{6}}$ </tex-math></inline-formula> cm/s. The device with a <inline-formula> <tex-math notation="LaTeX">${L}_{\text {G}}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">$0.15 ~\mu \text{m}$ </tex-math></inline-formula> demonstrates a high <inline-formula> <tex-math notation="LaTeX">${f}_{\text {T}}$ </tex-math></inline-formula> of 29 GHz and <inline-formula> <tex-math notation="LaTeX">${f}_{\text {max}}$ </tex-math></inline-formula> of 35 GHz, whilst preserving the high-voltage operation capability with a drain-to-source breakdown voltage (<inline-formula> <tex-math notation="LaTeX">$BV_{\text {DS}}{)}$ </tex-math></inline-formula> of 193 V. RF performance was verified by the power amplifying capability with a maximum power gain of 7 dB at 2 GHz for the device with <inline-formula> <tex-math notation="LaTeX">${L}_{\text {G}}$ </tex-math></inline-formula> of <inline-formula> <tex-math notation="LaTeX">$0.5~\mu \text{m}$ </tex-math></inline-formula>.

Youdou Zheng

Papers

Suppression and compensation effect of oxygen on heavily boron doping behavior in diamond films

Method for removing burrs of battery electrode plates by inductively coupled plasma dry etching

Low Leakage Current and High Breakdown Field AlGaN/GaN MIS-HEMTs Using PECVD-SiNx as a Gate Dielectric

The Growth and In-Situ Doping of SiGe/Si Strained Heterostructures by RTP/VLP-CVD

High-Voltage β-Ga2O3 RF MOSFETs With a Shallowly-Implanted 2DEG-Like Channel