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Proceedings Paper

Junction temperature in light-emitting diodes assessed by different methods
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Paper Abstract

The junction temperature of red (AlGaInP), green (GaInN), blue (GaInN), and ultraviolet (GaInN) light-emitting diodes (LEDs) is measured using the temperature coefficients of the diode forward voltage and of the emission-peak energy. The junction temperature increases linearly with DC current as the current is increased from 10 mA to 100 mA. For comparison, the emission-peak-shift method is also used to measure the junction temperature. The emission-peak-shift method is in good agreement with the forward-voltage method. The carrier temperature is measured by the high-energy-slope method, which is found to be much higher than the lattice temperature at the junction. Analysis of the experimental methods reveals that the forward-voltage method is the most sensitive and its accuracy is estimated to be ± 3°C. The peak position of the spectra is influenced by alloy broadening, polarization, and quantum confined Stark effect thereby limiting the accuracy of the emission-peak-shift method to ±15°C. A detailed analysis of the temperature dependence of a tri-chromatic white LED source (consisting of three types of LEDs) is performed. The analysis reveals that the chromaticity point shifts towards the blue, the color-rendering index (CRI) decreases, the color temperature increases, and the luminous efficacy decreases as the junction temperature increases. A high CRI > 80 can be maintained, by adjusting the LED power so that the chromaticity point is conserved.

Paper Details

Date Published: 7 March 2005
PDF: 9 pages
Proc. SPIE 5739, Light-Emitting Diodes: Research, Manufacturing, and Applications IX, (7 March 2005); doi: 10.1117/12.593696
Show Author Affiliations
Sameer Chhajed, Rensselaer Polytechnic Institute (United States)
Yangang Xi, Rensselaer Polytechnic Institute (United States)
Thomas Gessmann, Rensselaer Polytechnic Institute (United States)
Jing-Qun Xi, Rensselaer Polytechnic Institute (United States)
Jay M. Shah, Rensselaer Polytechnic Institute (United States)
Jong Kyu Kim, Rensselaer Polytechnic Institute (United States)
E. Fred Schubert, Rensselaer Polytechnic Institute (United States)

Published in SPIE Proceedings Vol. 5739:
Light-Emitting Diodes: Research, Manufacturing, and Applications IX
Steve A. Stockman; H. Walter Yao; E. Fred Schubert, Editor(s)

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