Journal Tips from the American Institute of Physics: June 14, 2012

Newswise — The following are brief summaries of papers recently accepted for publication in journals of the American Institute of Physics (AIP): AIP Advances, Applied Physics Letters, and Review of Scientific Instruments.

1. Researchers “Heal” Plasma-damaged Semiconductor with Treatment of Hydrogen Radicals2. Relocating LEDs from Silicon to Copper Enhances Efficiency3. Elemental and Magnetic Imaging Using X-rays and a Microscope

Copies of papers are available to journalists upon request at [email protected].

***********

1. Researchers “Heal” Plasma-damaged Semiconductor with Treatment of Hydrogen Radicals

Gallium nitride (GaN) is a highly promising material for a wide range of optical and high-power electronic devices, which can be fabricated by dry etching with plasmas. However, the plasma-induced defects and surface residues that remain after such processes tend to degrade the optical and electrical properties of the devices. A team of Japanese researchers has developed and tested a new way to “heal” such defects. The team exposed plasma-damaged GaN to hydrogen (H) radicals at room temperature. After testing various doses of H radicals, the researchers evaluated the optical properties of the GaN. The intensity of light emitted when electrons near the edge of the valence shell in GaN absorbed and then re-emitted photons drastically decreased after chlorine plasma-beam etching. After treatment with the higher-level doses of H radicals, however, the photoluminescence was restored to almost the level of un-etched GaN. The H radicals likely terminated the dangling bonds of Ga on the GaN surface, as well as desorbed the surface residues, which both led to the recovered optical performance. A key characteristic of the new healing process, described in a paper accepted to the American Institute of Physics’ journal AIP Advances, is that it is performed in situ immediately after the etching process. This is important because unwanted surface oxidation can easily occur on plasma-damaged GaN that is exposed to air.

TITLE: “Photoluminescence recovery by in-situ exposure of plasma-damaged n-GaN to atomic hydrogen at room temperature”JOURNAL: AIP Advances (aipadvances.aip.org)AUTHORS: Shang Chen (1), Yi Lu (1), Ryosuke Kometani (1), Kenji Ishikawa (1), Hiroki Kondo (1), Yutaka Tokuda (2), Makoto Sekine (1), and Masaru Hori (1)

(1) Nagoya University, Japan(2) Aichi Institute of Technology, Japan

2. Relocating LEDs from Silicon to Copper Enhances Efficiency

Chinese researchers have succeeded in transferring gallium nitride (GaN) light-emitting diodes (LEDs) grown on a layer of silicon to a layer of copper. The new copper substrate enabled the GaN crystals to release some of the internal stresses generated when they originally formed. This relaxation helped minimize the so-called “quantum confined stark effect,” a vexing problem for LEDs that reduces their efficiency. In comparison with LEDs on silicon substrates, the light output of LEDs on copper was enhanced by 122 percent. The relocation of the LEDs produced no obvious deterioration in the crystals’ light-emitting region, known as multiple quantum wells. The researchers attributed the improvements in efficiency to the removal of the absorptive substrate; the insertion of a metal reflector between the LEDs’ structure and the copper submount; the elimination of electrode shading, which also reduces efficiency; and the rough surface of the exposed buffer layer, which improves crystal orientation on the substrate. The results are reported in a paper accepted for publication in the American Institute of Physics’ journal Applied Physics Letters.

TITLE: “Crack-free InGaN multiple quantum wells light-emitting diodes structures transferred from Si (111) substrate onto electroplating copper submount with embedded electrodes”JOURNAL: Applied Physics Letters (apl.aip.org) AUTHORS: Tufu Chen (1), Yunqian Wang (1), Peng Xiang (1), Ruihon Luo (1), Minggang Liu (1), Weimin Yang (1), Yuan Ren (1), Zhiyuan He (1), Yibin Yang (1), Weijie Chen (1), Xiaorong Zhang (1), Zhisheng Wu (1), Yang Liu (1), and Bijun Zhang (1)

(1) Sun Yat-sen University, Guangzhou, China 3. Elemental and Magnetic Imaging Using X-rays and a Microscope

A team of researchers has developed a new microscope that can image the elemental and magnetic properties of a wide range of energy-important materials that are used in devices such as solar cells and solid-state lighting. The imager is based on a technique known as X-ray excited luminescence microscopy (XELM). It was created by hitching a standard optical microscope to a synchrotron X-ray source. Synchrotrons produce X-rays and other forms of electromagnetic radiation by sending electrons on a curved path at nearly the speed of light. When the X-rays strike the material being imaged, some of them are absorbed, which causes the sample to luminesce. The microscope portion of the imager is able to detect differences in this luminescence, which is directly related to both the elements in the sample and their magnetic properties. This technique combines the spatial resolution of optical microscopy with the element and magnetic specificity and precision of synchrotron radiation. It is able to spatially resolve features as small as one micron. However, this value was degraded in practice due to vibrations or subtle shifting of the systems used to direct the X-ray beam, though future refinements should alleviate any stability issues. XELM has some advantages over other techniques in that it is especially useful at low temperatures and can image in the presence of electric and magnetic fields. The results were accepted for publication in the American Institute of Physics’ journal Review of Scientific Instruments.

TITLE: “Elemental and magnetic sensitive imaging using x-ray excited luminescence microscopy”JOURNAL: Review of Scientific Instruments (rsi.aip.org)AUTHORS: R.A. Rosenberg (1), S. Zohar (1), D. Keavney (1), R. Divan (2), D. Rosenmann (2), A. Mascarenhas (3), and M.A. Steiner (3)

(1) Advanced Photon Source, Argonne National Laboratory, Argonne, Ill.(2) Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Ill.(3) National Renewable Energy Lab, Golden, Colo.About American Institute of PhysicsThe American Institute of Physics (AIP) is an organization of 10 physical science societies, representing more than 135,000 scientists, engineers, and educators. As one of the world's largest publishers of scientific information in physics, AIP employs innovative publishing technologies and offers publishing services for its Member Societies. AIP's suite of publications includes 15 journals, three of which are published in partnership with other organizations; magazines, including its flagship publication Physics Today; and the AIP Conference Proceedings series. Through its Physics Resources Center, AIP also delivers valuable services and expertise in education and student programs, science communications, government relations, career services for science and engineering professionals, statistical research, industrial outreach, and the history of physics and other sciences.