InGaN/GaN multiple-quantum-well light-emitting diodes have been fabricated on the (1010) m-plane of 4H-SiC substrates. The c-axes of the m-plane epitaxial films and the substrate are parallel. The surface of the epitaxial films has a ridged texture with the ridges aligned perpendicular to the c-axis. Xray diffraction shows superlattice features from the multiple-quantum well stack, and plan-view transmission electron microscopy shows a threading dislocation density of ~ 1010 cm-2 and a basal plane stacking fault density of ~ 8 × 106 cm-1. The electroluminescence from the LED shows a strong polarization anisotropy with the majority of the light emitted perpendicular to the c-axis and a polarization ratio exceeding 0.8. The temperature dependence of the polarization ratio shows a 49 meV difference in energy gap between the valence band minima with different polarizations.
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.
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.
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