Junction temperature analysis in green light emitting diode dies on sapphire and GaN substrates

We investigate pn-junction heating in 525 nm green GaInN/GaN quantum well light emitting diode dies by micro-Raman and photoluminescence spectroscopy. We compare dies grown on GaN and sapphire substrates of different sizes at current densities up to 267 A/cm2. Analysis of the experiments was supported by realistic three-dimensional finite-element simulations of the thermal properties. Sapphire based LED dies reach a junction temperature as high as 240 °C at a current density of 133 A/cm2, while those on bulk GaN only heat to 83 °C. This corresponds to a thermal resistance of 428 K/W and 63 K/W, respectively. By help of this calibration, the role of junction temperature in the spectral light output performance is identified. From the numerical simulation, dimensions and thermal conductivity of the substrate are identified as the dominant control parameters. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)