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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.techfore.2009.04.004 Byline: Yuya Kajikawa, Yoshiyuki Takeda Keywords: Citation network; Bibliometrics; Research front; Research evaluation; Organic light-emitting diodes Abstract: The field of organic light-emitting diodes (OLEDs) is an emergent research domain because of both scientific interest in chemistry and condensed matter physics and industrial importance as flat panel displays. In this paper, we analyzed a citation network of OLED papers and used a topological clustering method to investigate the structure of research and to detect emerging research domains. We found that most papers belong to two main clusters: organics and polymers. These two clusters have distinctive differences in subcluster structures and journals where papers are published. Supposing this discrepancy to indicate research progress, organics are in the applied research stage, while polymers are in the basic research stage. Author Affiliation: Innovation Policy Research Center, Institute of Engineering Innovation, School of Engineering, the University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan Article History: Received 27 February 2009; Revised 25 March 2009; Accepted 12 April 2009

A boost converter with buck-store and boost-restore (BSBR) technique fabricated by 0.25 [micro]m CMOS BCD process can provide different supply voltages to drive series red, green, and blue LEDs in sequence for reducing the power consumption on the constant current generator. The proposed technique not only stores and restores extra energy during the transient time of the reference tracking response to improve the efficiency but also enhances the reference tracking response to greatly reduce load transition time. Experimental results show that the period of reference tracking response can be improved. When the load current is 100 mA, the periods of reference down-tracking and up-tracking are smaller than 10 and 20 [micro]s, respectively. Furthermore, this technique can also provide a regulated voltage to drive the subblock implemented in the liquid crystal display system. The maximum efficiency of charge recycling is up to 94%, and the maximum efficiency of this boost converter is 94.5%. Experimental results demonstrate fast and efficient reference tracking performance is achieved by the proposed BSBR technique. Index Terms--Charge recycling, dc--dc converter, field color sequential (FCS), reference tracking.

Light emitting diodes (LEDs) incorporating InAs-GaSb superlattices (SLs) and multiple SL regions coupled with tunnel junctions are described. The studies have shown that saturation of optical output is because of both carrier leakage and Joule heating, with the latter being responsible for output limitations and device failure in large mesas.

A modified and improved optical feedback pixel driver circuit with only a few components and a wide range of [V.sub.data] voltages is presented. The performance of the circuit is verified by simulation using the HSPICE simulator, PSIA2 thin-film transistor (TFT) model and light-impact model of polycrystalline TFTs.

InGaN quantum well structures on GaN epilayers were exposed to 500 keV alpha particles to fluences above [10.sup.14] [cm.sup.2] to probe the relative radiation tolerance of the epilayer and wells. Performance was estimated by the intensity of ion-beam induced luminescence. Two separate types of quantum well structures emitted at 470 and 510 nm prior to irradiation, and only small wavelength shifts were observed even with the highest alpha fluences. Complementary cathodoluminescence experiments showed that luminescence in the quantum wells is strongly influenced by charges injected deep into the GaN epilayer. The 500 keV alpha penetration depth was ~1 [micro]m, so that defects were created at a faster rate in GaN compared to InGaN as alpha particles slowed and stopped within a minority carrier diffusion length of the quantum wells. However, the rate of luminescent decay was similar for both materials. Taken together with the cathodoluminescence data, this ion-beam induced luminescence comparison indicates that the quantum well luminescence decay rate is dominated by radiation-induced defects in the GaN epilayer. InGaN quantum wells are then demonstrated to be not more than a factor of ten more radiation sensitive than GaN, and may be substantially less sensitive than this upper bound. Index Terms--Alpha particle, InGaN, light-emitting diode, quantum well, radiation.

The extraction of guided modes from a standard light-emitting heterostructure similar to those of visible or near-infrared light-emitting diodes is discussed.

The characteristics of staggered InGaN quantum-well light-emitting diodes are discussed. Results suggest a significant improvement in output power and enhancement of radiative recombination rate.

Sidewall-deflector-integrated (SDI) light-emitting device (LED) is a device with deep and angled mesa sidewalls. Significant enhancement in the light output is observed in the SDI LEDs from the device surface.

The properties of resin-based composites cured with Light Emitting Diode (LED) lights are analyzed. Performances of six of the seven LED curing lights evaluated are similar to quartz-tungsten-halogen curing light in curing resin-based composites. Dentist can use depth of accuracy (DOC) of any curing light/resin-based composite/shade combination, as a reference to confirm that an adequate cure is achieved consistently over the life of curing lamp bulb, transformer, battery or LEDs or resin-based composite.

The results of the investigation of the glow discharge time and space development in the neon-filled diode at 4 mbar are presented. The glow is of the diffusion type with saturation current value 0.2 mA. The temporal development of current and light intensity of the 585.2-nm line (originated from the negative glow) emitted perpendicularly on the diode axis from different parts of the diode, are registered. Electrically registered (by the oscilloscope), the total current through the diode reaches the saturation for 3 ms, which corresponds to the formative time delay. On the other hand, the value of the formative time delay estimated statistically from the series of 5000 breakdowns is 4.7 ms. The difference in formative time delays is associated with the pre-breakdown current growth in the gap. The prebreakdown current is registered measuring the emitted light from diode gap. The investigation of light shows the increase of excitation in the gap at least 1.25 ms before any significant current is registered (I < 1 [micro]A). The negative glow appears in the diode gap and in the next a few milliseconds covers the cathode, which indicates the presence of the multiplication processes in diode. The stationary regime in the diode is established for about 10 ms. These results show the validity of the statistical approach in the breakdown time delay investigations and in the understanding the nature of the formative time delays. Index Terms--Electrical breakdown time delay, light emission, stages of formative time delay, temporal and spatial development.

Top-emitting OLEDs (organic light- emitting diodes) based on CuPc-TPD-Alq3 are investigated through the use of aluminum as anode and thin platinum (Pt) and praseodymium oxide (Pr2O3) as hole injection layer. The difference between top and bottom-emitting diodes is explained in terms of microcavity effects.

A novel switched-current (SI) memory circuit with improved accuracy and operating frequency for active-matrix organic light-emitting displays (AMOLEDs) is developed. The proposed SI memory circuit is suitable for current driving scheme-based high-resolution AMOLED applications.

A solution for the fabrication of low-voltage, low-power silicon light emitting devices, utilizing standard very large scale integration technology without any adaptation is presented. The structural details of two distinctly different line-patterned Si-LEDs are presented, composed of heavily doped n(super +)p(super +) junctions, made by BiCMOS n(super +) sinker and PMOS p(super +) source/drain doped regions respectively.

Nitride-based light-emitting diodes (LEDs) with Mg-doped In(sub 0.23)Ga(sub 0.77)N capping layers were successfully fabricated. The findings suggest that the output intensity of LEDs with In(sub 0.23)Ga(sub 0.77)N was much larger particularly at elevated temperatures.

Characteristics of a novel device based on the integration of quantum well IR photodetector (QWIP), a heterostructure bipolar transistor (HBT), and a light-emitting diode (LED) for up-conversion of middle infrared (IR) into near IR radiation is studied. The QWIP-HBT-LED up converter is the most advantageous for megapixel focal plane arrays and high read-out rate cameras.

A novel Ga(sub x)In1(sub 1-x)P tensile strain barrier reducing (TSBR) thin-film structure is grown between window and cladding layers of multi-quantum-well-AlGaInP light-emitting diodes (LEDs). This TSBR layer is of interest for improved power efficiency, reliability and global lifetime behavior of an LED-type device.

High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. Results showed that the 20-mA forward voltage could be reduced and the output intensity of the nitride-based green LEDs could be increased by increasing the growth temperature of GaN barrier layers from 700 degree celsius to 950 degree celsius.

A design of a flat-panel display (FPD) based on organic light-emitting diodes (OLEDs) and on organic thin-film transistors (OTFTs) is described. The suitability of the current organic light-emitting diode (OLED) and organic thin-film transistor (OTFT) technology for flat-panel display (FPD) technology is discussed.

The cost of high efficiency solar converters can be lowered by the use of a high energy flux. Thermophotonic (TPH) offers the possibility of high efficiency over 40% in the 100-1000 suns range, when the convergence of high- power fluxes is considered.

An extensive numerical model that has been recently developed for the multilayer organic light-emitting diode is described and is applied to study the number of real devices. The model has proved efficient for both qualitative and quantitative understanding of some organic light-emitting diodes (OLEDs) devices containing multilayer structures.

Exploiting of work function changes on acid and base treated indium tin oxide (ITO) anodes to alter the properties of light emitting devices is described. The UPS and surface photovoltage measurements are compared on a variety of device structures and a microscopic picture of interfacial modifications is built in explaining the current-voltage and brightness characteristics of organic light emitting diodes (OLEDs).

An analysis of the role of extended and point defects and key impurities such as C, O, and H, on the optical and electrical properties of GaN was conducted. The rapid development and commercialization of blue and green light-emitting diodes (LEDs) and the achievement of long-lifetime laser diodes was followed by realization of UV photodetectors and several different electronic devices. Continued rapid development in the areas of LEDs, laser diodes, microwave and digital electronic devices, UV detectors ad high voltage unipolar and bipolar devices is expected as an improved understanding of the defect and impurity issues in these materials evolve.

The electroluminescence (EL) spectrum and current-voltage (I-V) characteristics of a p-i-n resonant tunneling light emitting diode based on an AlGaAs/GaAs heterostructure are studied. It is shown that the multiple-line EL spectrum is due to the occupation of excited hole subbands and interactions between light and heavy holes. The current distability in the I-V relationship is due to charge accumulation in the central i-region.

A model based on Poisson's equation and conservation law of charges is derived to determine the characteristics of organic light emitting-diodes (OELDs). The model is used to determine current-voltage characteristics, relative quantum efficiency and emission distribution of OLEDs. Results show that at least one barrier height should be low for low voltage device operation. High brightness devices also require high mobility.