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.
New sources for heterogeneous nucleation of both <$110> and <110> extended screw-type misfit dislocations to relax the lattice shear stress on the ZnSxSe1-x/GaAs interface has been observed for the first time. These are identified as Shockley partial dislocations originating in areas close to the ZnSxSe1-x/GaAs interface. The Shockley partials form to accommodate the stacking errors produced upon island coalescence. In-situ electron beam- induced heating studies were carried out to observe the dislocation generation mechanism in the films. Our results show that the stress (sigma) approximately equals 1 X 109 dyne/cm2 stored in the ZnSxSe1-x films gives rise to bowing of the threading segments of the Shockley partials. The bowing result from the fact that the dislocations are pinned at the film/substrate interface and at the film surface. This process involves an increase in the length of the treading segments under the stress. With further accommodation of the lattice strain, the line tension of the bowing threading segments is relieved by the movement of the pinning points at the film surface accompanied by gliding of the threading segments toward the film/substrate interface. This process takes place by the movement of either one or both of the pinned points at the film surface. Finally, a segment of extended screw- type dislocation is generated when the segments of the Shockley partials reach the ZnSxSe1-x/GaAs interface. A <110> extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on (111)-type planes with Burger vectors b equals a/6<121>-type and a/6<211>-type toward the interface. On the other hand, a <110> extended screw-type interfacial dislocation is generated by gliding of the threading segments of the Shockley partials on (111)- type planes with Burger vectors b equals a/6<121>-type and a/6<211>-type toward the interface. Finally, the shear stress between film and substrate is relaxed by the generation of a grid of extended interfacial dislocations with screw components along the <110> and <110> directions.
Both Shockley and Frank partial dislocations originating at the ZnSxSe1-x/GaAs interface were observed with defect densities in the range less than 5 X 104/cm2 to approximately 1 X 108/cm2 for samples grown under different conditions. These faulted defects act as heterogeneous nucleation sites for the generation of 60 degree(s) misfit dislocations. A very low density of Shockley partial dislocations was obtained in ZnSxSe1-x films grown by the layer-by-layer mode on GaAs substrates. Also, the density of Frank partial dislocations was decreased by exposing the As- stabilized GaAs surface to Zn for 1-2 minutes prior to the growth of the ZnSxSe1-x epilayers. These samples contained a defect density lower than 5 X 104/cm2. A Ga2Se3 compound existing at the ZnSxSe1-x/GaAs interface is thought to be the source of the Frank partial dislocations.
Conference Committee Involvement (1)
Components and Packaging for Laser Systems XI
25 January 2025 | San Francisco, California, United States
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