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

We investigate the parameters in the band-anticrossing (BAC) model for GaNP and InGaPN in this work. The parameters in the BAC model for GaNP and InGaNP are obtained by fitting experimental data. It is found that the band gap bowing of In-GaNP is stronger than that of InGaNAs. The effects of annealing on the parameters in the BAC model for InGaNP are also discussed in this work. In addition, the origins for improving luminescence efficiency by annealing are explained. It is relative to the forming of more In-N clusters.

The parameters in the band-anticrossing model for In x Ga 1- x N y P 1- y before and after annealing

AlGaN/GaN-based planar Schottky barrier diodes with various spacings between ohmic and Schottky contacts are fabricated without any edge termination. The reverse leakage current of the devices quickly saturates at low reverse bias when the two-dimensional electron gas (2DEG) at the AlGaN/GaN interface is fully depleted. The corresponding breakdown voltage is found to follow a linear dependence on contact spacing and exceeds 1100 V at a contact spacing of 20 μm, yielding a high V2BR/RON value of > 280 MWcm−2. The observations are tentatively explained by a "natural super-junction" theory, in which ionized surface states at front surface of the AlGaN barrier have to be neutralized by reverse surface leakage current from the Schottky electrode.

http://iopscience.iop.org/article/10.1088/0256-307X/28/1/017303/pdf

A 1100 + V AlGaN/GaN-Based Planar Schottky Barrier Diode without Edge Termination

Homo-epitaxial growth of high crystal quality GaN thin films by plasma assisted–molecular beam epitaxy

https://iopscience.iop.org/article/10.7567/1882-0786/ab52cc/pdf

Investigations of the gate instability characteristics in Schottky/ohmic type p-GaN gate normally-off AlGaN/GaN HEMTs

In many critical civil and emerging military applications, low-level UV detection, sometimes at single photon level, is highly desired. In this work, a mesa-type 4H-SiC UV avalanche photodiode (APD) is designed and fabricated, which exhibits low leakage current and high avalanche gain. When studied by using a passive quenching circuit, the APD exhibits self-quenching characteristics due to its high differential resistance in the avalanche region. The single photon detection efficiency and dark count rate of the APD are evaluated as functions of discrimination voltage and over-drive voltage. The optimized operation conditions of the single photon counting APD are discussed.

http://iopscience.iop.org/article/10.1088/0256-307X/32/8/088503/pdf

Youdou Zheng

Papers

The parameters in the band-anticrossing model for In x Ga 1- x N y P 1- y before and after annealing

A 1100 + V AlGaN/GaN-Based Planar Schottky Barrier Diode without Edge Termination

Homo-epitaxial growth of high crystal quality GaN thin films by plasma assisted–molecular beam epitaxy

Investigations of the gate instability characteristics in Schottky/ohmic type p-GaN gate normally-off AlGaN/GaN HEMTs

Discrimination Voltage and Overdrive Bias Dependent Performance Evaluation of Passively Quenched SiC Single-Photon-Counting Avalanche Photodiodes