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

Abstract

We analyze experimentally and theoretically the thermal characteristics of 470 nm 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 (Tj) 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 (Rth), 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 Tj values of LEDs are theoretically calculated as 392.7 and 578 K for 450 ×450 and 250 ×250 µm2, respectively. The thermal 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 Rth of < 75 K/W for 450 ×450 µm2 LED. The Rth 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 Rth of LEDs.