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Indium incorporation into strained InGaN coherently grown on a GaN substrate with arbitrary polarity is simulated using a simplified epitaxy model. The InGaN composition is predicted as a function of C-axis inclination angle. Effect of strain originated from the lattice mismatch on optical transitions in the bulk InGaN and quantum wells is examined with account of both complex valence band structure and polarization charges induced at the InGaN/GaN interfaces. A higher indium incorporation on nonpolar and semipolar planes, as compared to the ordinary C-plane, is found to not necessarily result in a longer emission wavelength.

Strain effect on indium incorporation and optical transitions in bulk InGaN and GaN/InGaN/GaN quantum wells (QWs) coherently grown on GaN substrates with different orientations of hexagonal axis is studied by simulation. The strain modification in the nonpolar and semipolar structures, as compared to polar ones, is found to result in both a higher indium percentage in the InGaN alloy and a larger materials bandgap, producing opposite trends in variation of the optical transition energy (emission wavelength) with the crystal orientation. The interplay between the effects is discussed in view of development of green-light emitters. A possible way for controlling the strain in the InGaN layers and QWs and thus the emission wavelength is considered and tested by modelling. 0 15 30 45 60 75 90 2.3 2.4 2.5 2.6 2.7 2.8 InGaN SQW on relaxed In 0.08 Ga 0.92 N 520 nm Transition energy (eV) C-axis inclination angle (degrees) InGaN SQW on GaN 475 nmOptical transition energy of the same single InGaN QW grown on either GaN or relaxed In 0.08 Ga 0.92 N sublayer as a function of the crystal C-axis inclination to epitaxial layer plane.

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.

We have applied simulations to study current the spreading and heat transfer in blue III-nitride lightemitting diodes (LEDs) with the focus on self-heating and its effect on the device characteristics. A conventional planar design of an LED die is considered for the heat sink through a sapphire substrate. The computations predict a great current crowding at the contact electrode edges, resulting in a non-uniform temperature distribution over the die. The thermal effect on the current-voltage characteristic, output optical power, and series resistance of the diode is analyzed and the theoretical predictions are compared with available observations.1 Introduction Planar chip design with on-one-side n-and p-contact electrodes is commonly employed in most III-nitride LEDs. Such a chip configuration leads to a considerable current crowding near the electrode edges and, as a result, to in-plane non-uniformity of the electroluminescence intensity. In addition, the non-uniform current spreading over an LED die induces a local overheating of the device heterostructure, lowering its internal quantum efficiency (IQE). Being recognized as an important factor limiting the LED performance, the current crowding in III-nitride light emitters was in the focus of numerous studies (see, e.g., [1] and references therein). However, there is still lack of understanding of factors controlling the LED self-heating and its effect on the device characteristics, including currentvoltage (I-V) characteristic, output power, external and wall-plug efficiency (WPE), series resistance of the diode, and emission spectra. This paper reports on a self-consistent modeling analysis of the current spreading and heat transfer in blue LED dice. For this purpose, coupled three-dimensional simulation is performed based on the hybrid approach suggested in [1].