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.

. Pn, 81.05.Rm, 72.80.Ey We review key aspects of sublimation growth of wide-bandgap semiconductors like SiC, AlN and GaN, and show how modeling can help to solve a number of practical problems. As the temperature distribution in the growth chamber is the most critical factor in the sublimation technology, we discuss in detail specific features of heat transfer with the focus on the porous materials normally involved in the growth system: powder source, thermal insulation, and graphite. The species transport is simulated using advanced models accounting for a multicomponent vapor and the kinetics of chemical interaction of nitrogen-containing species with the surface of group-III nitrides. The effect of growth conditions on parasitic phase formation is analyzed. To optimize the growth system design and operating conditions, we suggest an inverse-problem approach instead of commonly used trial-and-error methods. This simulation procedure has proved quite efficient for getting design solutions, which could hardly be found by conventional straightforward methods. In particular, we demonstrate the effectiveness of the inverse modeling for finding the growth conditions, which provide crystals of desired shapes. A special analysis is made to establish a correlation between the growth conditions and defect distribution in the grown crystal, with the focus on thermoelastic stress produced by temperature gradients. The high-temperature dynamics of gliding dislocations and consequent plastic stress relaxation in the material is examined. The prospective of global modeling of wide-bandgap crystal growth by sublimation and still open questions are discussed.

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