Let there be (a new kind of) light [NEWS]

Recent events on the business front and advances in the lab could soon transform the way about lighting our homes and buildings. Significant strides in developing organic light-emitting diodes (OLEDs) may allow architects in the next few years to integrate this power-efficient and tractable technology into basic building materials, enabling entire structures to be turned into luminous edifices. Konica Minolta Holdings, a Tokyo-based manufacturer of imaging products, and General Electric Co., one of the world's largest lightbulb makers, formed a strategic alliance to accelerate development of OLED lighting and vowed to ship products in the next three years. A major challenge all OLED manufacturers face is how to make their products cost-competitive with the ultracheap incandescent and fluorescent lighting products on the market.     

Ligth from silicon [LED]

This paper discusses the current efforts to develop an electrically powered silicon laser for the fabrication of light emitting diodes (LED). Researchers have been pushing two strategies in their quest to get light out of silicon. One scheme is based on a curious effect called quantum confinement, which reduces silicon's momentum problem and increases the probability that injected electrons will produce photons. The other scheme sidesteps silicon's bandgap problems by having another material, embedded within the silicon device, emit the light. This paper proposes a combination of both techniques to produce light emitters that operate at room temperature with a controllable tradeoff between high efficiency and long lifetime. A key advantage of this approach is that the color of the light emitted depends on the rare-earth ions used. Unfortunately, this approach produces low light output because the maximum output power is limited by how densely the device can be packed with rare-earth ions. Nevertheless, researchers are confident that, within a few years, an electrically driven silicon laser will become a reality.     

The great gallium nitride gamble

Pure, clear wafers of this material are the key to blue and ultraviolet semiconductor lasers for next-generation DVDs.     

Emerging gallium nitride based devices

Wide bandgap GaN has long been sought for its applications to blue and UV emitters and high temperature/high power electronic devices. Recent introduction of commercial blue and blue-green LED's have led to a plethora of activity in all three continents into the heterostructures based on GaN and its alloys with AlN and InN. In this review, the status and future prospects of emerging wide bandgap gallium nitride semiconductor devices are discussed. Recent successes in p-doping of GaN and its alloys with InN and AlN, and in n-doping with much reduced background concentrations have paved the way for the design, fabrication, and characterization of devices such as MESFET's, MISFET's, HBT's, LED's, and optically pumped lasers. We discuss the electrical properties of these devices and their drawbacks followed by future prospects. After a short elucidation of materials characteristics of the nitrides, we explore their electrical transport properties in detail. Recent progress in processing such as formation of low-resistance ohmic contacts and etching is also presented. The promising features of quarternaries and double heterostructures in relation to possible current injection lasers, LED's, and photodetectors are also elaborated on     

Low- and high-frequency capacitance of aluminum gallium nitride/gallium nitride heterostructures with interface traps

We have studied frequency dependence of capacitance properties of aluminum gallium nitride/gallium nitride (AlGaN/GaN) heterostructures with interface traps at the AlGaN/GaN interface. We have shown that ability of charge in interface traps to respond to external measuring signal is responsible for the frequency dispersion of capacitance curves. The difference between capacitance curves measured at low and high frequencies in experimental structures is similar to the difference between simulated capacitances of the heterostructures with interface traps measured at low and high frequencies. At a high frequency when the charge in interface traps does not follow the measuring signal, the capacitance curves are only shifted in voltage compared to the curve of the structure without interface traps. But for low frequency a capacitance peak is observed. Interface traps hence contribute to experimentally observed capacitance dispersion.     

Experimental gallium nitride microwave Doherty amplifier

The combination of gallium nitride (GaN) device technology with the now well established efficiency enhancing Doherty power amplifier (PA) architecture is presented for the first time. The experimental structure exhibits a power density of approximately 1 W/mm and linearity that remains comparable to that observed in other GaAs structures, demonstrating that GaN can be highly effective when used within this type of PA architecture.     

Doping of gallium nitride using disilane

The silicon doping of n-type GaN using disilane has been demonstrated for films grown on sapphire substrates by low pressure organometallic vapor phase epitaxy. The binding energy of an exciton bound to a neutral Si donor has been determined from low temperature (6K) photoluminescence spectra to be 8.6 meV. Nearly complete activation of the Si impurity atom in the GaN lattice has been observed.     

Lighting up the Andes [LED lamps]

This work relates how a pair of 62-year olds from Canmore, Alberta in Canada, have made it their mission to free remote communities from reliance on costly kerosene lighting. Anthony and Faith Harckham have developed a simple LED lamp which consumes only 1 watt and produces 30 lumens in a focused beam about as bright as the light of a 20 W incandescent bulb. The couple devised a small volunteer operation that blends tourism and charity. Called Luxtreks, the operation has installed lighting systems in more than 700 rural homes in Bolivia, Guatemala, Peru and Pakistan without taking a dime of government money. The trekers travel with the couple and personally deliver their gift by installing the LED lamps themselves. At the same time, the trip provides trekkers a unique, in situ experience about as culturally distant from their daily lives as they could have imagined.     

Reactive ion etching of gallium nitride films

Reactive ion etching (RIE) was performed on gallium nitride (GaN) films grown by electron cyclotron resonance (ECR) plasma assisted molecular beam epitaxy (MBE). Etching was carried out using trifluoromethane (CHF₃) and chloropentafluoroethane (C₂ClF₅) plasmas with Ar gas. A conventional rf plasma discharge RIE system without ECR or Ar ion gun was used. The effects of chamber pressure, plasma power, and gas flow rate on the etch rates were investigated. The etch rate increased linearly with the ratio of plasma power to chamber pressure. The etching rate varied between 60 and 500Å/min, with plasma power of 100 to 500W, chamber pressure of 60 to 300 mTorr, and gas flow rate of 20 to 50 seem. Single crystalline GaN films on sapphire showed a slightly lower etch rate than domain-structured GaN films on GaAs. The surface morphology quality after etching was examined by atomic force microscopy and scanning electron microscopy.     

Plasma etch-induced conduction changes in gallium nitride

The effect of plasma-etching damage on carrier transport properties in GaN has been studied under various plasma conditions by monitoring the changes in sheet resistivity (ρ _s) and mobility (μ _s) or the resistivity (R). All the etching experiments were performed in an electron cyclotron resonance microwave plasma reactive ion etching (ECR-RIE) system. Consistent changes in the transport properties have been observed with increasing dc bias (ion energy) in all plasmas except in those containing chlorine. With noble gas plasmas, the largest change in conductance was created when Ar, the heaviest ion, was accelerated to its highest voltage. In these Ar sputtering cases, substantial surface micro-roughening has been observed. These surfaces also display considerable nitrogen deficiency as measured by Auger electron spectroscopy. These observations suggest that preferential sputtering of nitrogen from the surface of GaN is one form of ion damage. The other is displacement damage. Both of these forms of ion damage are considered to be the direct cause of the observed changes in the electrical properties.     

Flow modulation epitaxy of indium gallium nitride

InGaN layers were grown on GaN films by flow modulation epitaxy (FME) using the precursors trimethylgallium, trimethylindium, and ammonia. The indium composition of the FME grown layers was generally lower than of films grown under the same conditions in the continuous growth mode, but which had been of poor optical quality. The indium incorporation efficiency increased with decreasing ammonia flush time, increasing ammonia flow during group-III injection, and increasing group-III precursor injection time. Films grown under optimized conditions showed intense band edge related luminescence at room temperature up to a wavelength of 465 nm. Atomic force microscopy investigations revealed a strong dependence of the surface morphology of the InGaN films on the growth mode.     

The blinking light [reflections]

I was considering buying a new desktop computer, and I thought I had found the ideal model. That is, until I noticed that one little thing was missing?the activity light for the hard drive. The manufacturer probably saved a few cents by leaving it out, but that little light was of some psychological importance to me. How could I possibly buy a computer that was just going to sit there and not give me any indication that it was working?     

Alternative precursor systems for the MOCVD of aluminium nitride and gallium nitride

Two alternative precursor systems have been investigated for the growth of AlN and GaN by MOCVD. The first involved the reaction between Me₃M (M(DOUBLE BOND)Al, Ga) and tert-butylamine (^tBuNH₂), whilst the second route involved the pyrolysis of single-source precursors such as Me₃M(NH₃) (M(DOUBLE BOND)Al, Ga) and [Me₂Ga(NH₂)]₃. Both routes proved suitable for the deposition of AlN thin films, and epitaxial AlN layers have been deposited on sapphire (0001) from Me₃Al(NH₃) without any added NH₃. Attempts to grow GaN from Me₃Ga/^tBuNH₂ mixtures or Me₃Ga(NH₃) were unsuccessful, leading to the deposition of Ga droplets, although GaN films containing a large excess of Ga were deposited by low-pressure MOCVD from the single-source precursor [Me₂Ga(NH₂)]₃.     

Who goes there? [personal identity systems]

Just a few years ago, getting to work involved a nod to someone in the building lobby or a wave to an office receptionist. Today, those friendly greetings have been replaced in many offices by smart cards. Soon the use of smart cards at these sites is expected to make way for biometric identifiers: handprints, fingerprints, eye scans, or face-recognition signatures. On the way to work, too, one's face or car may be scanned or photographed at traffic signals, bank machines, shopping malls, parks, and sidewalks. As methods of identification, however, biometric technologies are still immature and are still capable of being defeated.     

让存储变得更容易--CA数据保护解决方案全面上市

目前,还有相当一部分企业认为,数据备份就像买保险,也许永远不会用到,因此不愿意在这上面花费大笔的经费.常言道"人无远虑,必有近忧",在当今的世界中,各种潜在的灾难,如火灾、水灾、硬件故障、人员失误、病毒感染,甚至一次小小的停电事故,都可能会对数据构成威胁,企业必须为此做出充分的准备.为了使国内的企业用户对数据存储管理解决方案有一个详细的了解,记者近日采访了刚刚推出最新数据保护解决方案BrightStor ARCserve Backup rll (以下简称BAB rll)的CA公司.     

Hydride vapor phase epitaxy for gallium nitride substrate

Due to the remarkable growth rate compared to another growth methods for gallium nitride(GaN)growth,hydride vapor phase epitaxy(HVPE)is now the only method for mass product GaN substrates.In this review,commercial HVPE systems and the GaN crystals grown by them are demonstrated.This article also illustrates some innovative attempts to develop homebuilt HVPE systems.Finally,the prospects for the further development of HVPE for GaN crystal growth in the future are also discussed.