Optical cavity effects have a significant influence on the extraction efficiency of InGaN/GaN quantum-well-heterostructure flip-chip light-emitting diodes (FCLEDs). Light emitted from the quantum well (QW) self-interferes due to reflection from a closely placed reflective metallic mirror. These interference patterns couple into the escape cone and cause significant changes in the extraction efficiency as the distance between the QW and the metallic mirror varies. In addition, the radiative lifetime of the QW also changes as a function of the distance between the QW and the mirror surface. Experimental results from packaged FCLEDs, supported by optical modeling, show that a QW placed at a neighboring position corresponding to a minimum in overall light extraction. Furthermore, the optical model and experimental data are used to estimate the absolute internal quantum efficiency.
We have demonstrated hole injection through a tunnel junction embedded in the GaN-based light emitting diode structure. The tunnel junction consists of 30 nm GaN:Si++ and 15 nm InGaN:Mg++ grown on a GaN-InGaN quantum well heterostructure. The forward voltage of the light emitting diode, included the voltage drop across the reverse-biased tunnel junction, is 4.1 V at 50 Z/cm$_2), while that of a standard light emitting diode with a conventional contact structure is 3.5 V. The light output of the diode with the tunnel junction is comparable to that of the standard device. We then employed the tunnel junction in vertical cavity surface emitting laser structures and dual-wavelength light emitters. In the vertical cavity structure, a good lateral current spreading was accomplished, resulting in uniform emission pattern. The dual-wavelength light emitter has been operated as a three- terminal device with independent electrical control of each LEDs to a nsec time scale.
Jonathan Wierer, Jerome Bhat, Chien-Hua Chen, G. Christenson, Lou Cook, M. Craford, Nathan Gardner, Werner Goetz, R. Scott Kern, Reena Khare, A. Kim, Michael Krames, Mike Ludowise, Richard Mann, Paul Martin, Mira Misra, J. O'Shea, Yu-Chen Shen, Frank Steranka, Steve Stockman, Sudhir Subramanya, S. Rudaz, Dan Steigerwald, Jingxi Yu
High-power light-emitting diodes (LEDs) in both the AlInGaP (red to amber) and the AlGaInN (blue-green) material systems are now commercially available. These high-power LEDs enable applications wherein high flux is necessary, opening up new markets that previously required a large number of conventional LEDs. Data are presented on high-power AlGaInN LEDs utilizing flip-chip device structures. The high-power flip-chip LED is contained in a package that provides high current and temperature operation, high reliability, and optimized radiation patterns. These LEDs produce record powers of 350 mW (1A dc, 300 K) with low (<4V) forward voltages. The performance of these LEDs is demonstrated in terms of output power, efficiency, and electrical characteristics.
Mari Ochiai-Holcomb, Michael Krames, Gloria Hofler, Carrie Carter-Coman, Eugene Chen, Patrick Grillot, Kwang Park, Nathan Gardner, Jen-Wu Huang, Jason Posselt, David Collins, Steve Stockman, M. Craford, Frederick Kish, I. Tan, Tun Tan, Christophe Kocot, Mark Hueschen
High power light emitting diodes (LEDs) are of interest for many lighting applications. Flux improvements can be achieved by scaling conventional chips to larger dimensions. However this scaling results in a decrease in extraction efficiency. These penalties can be offset by modifying the chip geometry such that the number of internal reflections is reduced, thereby increasing the probability of photon escape. LEDs with a truncated-inverted-pyramid (TIP) geometry have been fabricated and packaged. Peak efficiencies exceeding 100 lm/W have been measured (100 mA dc, 300 K) for orange ((lambda) p approximately 610 m) devices. In the red wavelength regime ((lambda) p approximately 650 nm), peak external quantum efficiencies of 55% (100 mA dc, 300 K) have been achieved. Flux exceeding 65 lumens from a single 594 nm device has also been demonstrated. These characteristics match and/or exceed the performance of many conventional lighting sources.
Steven Maranowski, Michael Camras, Changhua Chen, Lou Cook, M. Craford, Dennis DeFevere, Robert Fletcher, Gloria Hofler, Frederick Kish, Chihping Kuo, A. Moll, Tim Osentowski, K. Park, Michael Peanasky, S. Rudaz, Dan Steigerwald, Frank Steranka, Steve Stockman, I. Tan, J. Tarn, Jingxi Yu, Mike Ludowise, Virginia Robbins
A new class of LEDs based on the AlGaInP material system first became commercially available in the early 1990's. These devices benefit from a direct bandgap from the red to the yellow-green portion of the spectrum. The high efficiencies possible in AlGaInP across this spectrum have enabled new applications for LEDs including automotive lighting, outdoor variable message signs, outdoor large screen video displays, and traffic signal lights. A review of high-brightness AlGaInP LED technology will be presented.
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