Coupled modeling of current spreading, thermal effects and light extraction in III-nitride light-emitting diodes

A hybrid approach to modeling of electrical, optical and thermal processes in state-of-the-art light-emitting diodes (LEDs) is described in detail. The advantages of the approach are demonstrated with reference to an interdigitated multipixel array (IMPA) chip design recently suggested to improve the LED performance at high-current operation. Such an LED, consisting of a hundred single-pixel light sources integrated on a common substrate, has a rather complex multi-scale geometry challenging for a coupled analysis of the device operation. The hybrid approach is found to enable coupled simulation of the current spreading, heat transfer and light emission in the IMPA LED at a modest demand of computer resources and computing time. Specific features of the IMPA LED operation are discussed in terms of modeling and compared with those of a conventional square-shaped LED. The impact of current crowding on the uniformity of light emission from the dice of both types is examined. A dramatic difference in the series resistance of the IMPA and square-shaped LEDs is explained on the basis of current spreading analysis. The active region overheating is found to be a critical factor eventually limiting the output optical power of the square LED. Good agreement between the theoretical predictions and observations is demonstrated, which justifies the use of the hybrid approach.