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 microstructures of the Ge-dots/Si multilayered structure films fabricated by metal-induced lateral crystallization (MILC) have been investigated. The micro-Raman spectroscopy, optical microscopy and electron microscopy observations reveal that the crystallized Si film has large leaf-like grains elongated along the lateral crystallization direction, which shows (110) preference. Furthermore, this preference is found to deliver to different Si layers of the multilayered structures to have an identical crystalline orientation. The strain shift of Ge dots as deduced from Raman spectroscopy reveals a formation of a high-quality interface between the crystallized Si and Ge-dot

Microstructures of Ge-dots/Si multilayered structures fabricated by Ni-induced lateral crystallization

InGaN/GaN multi-quantum-well (MQW) nanowires and accordingly light-emitting-diodes (LEDs) were fabricated on the n-GaN/sapphire substrate with a nano-patterned SiO 2 film as growth mask. The structural characteristics, optical and electrical properties were investigated. the observed results show that a InGaN/GaN MQW nanowire has smooth surface morphologies and triangular cross sectional structure. A strong cathodoluminescence emission peak related to InGaN/GaN MQW is observed located at 461 nm. In addition, InGaN/GaN MQW nanowire LED shows typical p-n junction characteristics with a low turn-on voltage, and its electroluminescence displays purplish.

InGaN/GaN multi-quantum-well nanowires and light emitting

GaN-based metal-ferroelectric-semiconductor (MFS) structure has been fabricated by using ferroelectric Pb(Zr0.53Ti0.47)O3 (PZT) instead of conventional oxides as gate insulators. The GaN and PZT films in the MFS structures have been characterized by various methods such as photoluminescence (PL), wide-angle X-ray diffraction (XRD) and high-resolution X-ray diffraction (HRXRD). The Electric properties of GaN MFS structure with different oxide thickness have been characterized by high-frequency C-V measurement. When the PZT films are as thick as 1 µm, the GaN active layers can approach inversion under the bias of 15V, which can not be observed in the traditional GaN MOS structures. When the PZT films are about 100 nm, the MFS structures can approach inversion just under 5V. All the marked improvements of C-V behaviors in GaN MFS structures are mainly attributed to the high dielectric constant and large polarization of the ferroelectric gate oxide.

Fabrication and characterization of metal-ferroelectric-GaN structures

Industrial power devices are required to conduct at least several amperes current in the on-state while blocking at least hundreds of volts in the off-state. In this work, high-temperature operational $\text{NiO}/\beta-\text{Ga}_{2}\mathrm{O}_{3}$ vertical p-n heterojunction diodes (HJDs) with ampere-level forward current and kV -level reverse breakdown voltage $(V_{b})$ have been demonstrated. The temperature-dependent current-voltage characteristics reveal that trap-assisted tunneling (TAT) current dominates the forward conduction mechanism of HJDs, while the leakage current is dominated by variable range hopping (VRH) mechanism under the high reverse bias. The resultant large-area (1×1 mm2) HJD rectifiers exhibit a superior forward on-state current of 5 A, a nearly-unity ideality factor and a large $V_{b}$ of 1.17 kV operated at a high temperature up to 548 K. The low deterioration rate of forward on-state current (1.24 mA/K at 4 V) and $V_{b}$ (0.95 V/K) with temperature implies high reliability of HJD, evidencing the promising potential of Ga2O3-based power diodes in harsh-environment power systems.

5 A/1.17 kV NiO/$\beta$-Ga2O3 heterojunction power rectifier with high-temperature operation capability up to 548 K

In this work, a lateral multichannel GaN-based junction field effect transistor (JFET) is proposed and studied by 3-D numerical simulation to realize normally- OFF operation and retain large output current simultaneously. Normally- OFF operation can be realized more easily due to the use of double side p-n junction gate for every single channel. We calculate the variations of the maximum saturation current and threshold voltage with channel thickness and doping concentration and obtain the corresponding transition chart from normally- ON to normally- OFF operation. Based on these optimized structure parameters, we further attempt electrical field transfer terminal technologies to improve the breakdown characteristics for the device, and we find that the drain field plate technology has much better effect than the reduced surface field technology, such that the drain field plate can transfer high electric field from the drain terminal into the insulation dielectric. The simulated breakdown voltage of the designed JFET with drain field plate reaches 880 V, leading to an increase by 50% compared to that without drain field plate. In addition, the designed device shows a relatively high cutoff frequency up to gigahertz.

Youdou Zheng

Papers

Microstructures of Ge-dots/Si multilayered structures fabricated by Ni-induced lateral crystallization

InGaN/GaN multi-quantum-well nanowires and light emitting

Fabrication and characterization of metal-ferroelectric-GaN structures

5 A/1.17 kV NiO/$\beta$-Ga2O3 heterojunction power rectifier with high-temperature operation capability up to 548 K

3-D Simulation Study of a Normally-OFF GaN Lateral Multi-Channel JFET With Optimized Electrical Field Transfer Terminal Structure