Thermal Analysis of InGaN/GaN Multiple Quantum Well Light Emitting Diodes with Different Mesa Sizes

We analyze experimentally and theoretically the thermal characteristics of 470nm InGaN/GaN light emitting diodes (LEDs) with different mesa sizes for efficient heat dissipation. For various mesa sizes, the junction temperature is measured as a function of injection current by the diode forward voltage method. The junction temperature (T-j) increases linearly with injection current and it rises rapidly with the reduction in mesa size. The thermal parameters, such as the junction temperature, temperature profile, and thermal resistance (R-th), are obtained from thermal simulations with the heat source density, determined from the measured light-current-voltage data, using a three dimensional heat dissipation model. At 200 mA, the T-j values of LEDs are theoretically calculated as 392.7 and 578 K for 450 x 450 and 250 x 250 mu m(2), respectively. The th ermal resistance is kept nearly constant due to a linear relationship between junction temperature and injection current and it is reduced as the mesa size increases, indicating a low R-th of < 75K/W for 450 x 450 mu m(2) LED. The R-th values obtained by the thermal simulation are fairly consistent with the experimental data. The use of the substrate with a relatively high thermal conductivity can also improve significantly the R-th of LEDs. (C) 2010 The Japan Society of Applied Physics