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.

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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.

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From the analysis of available experimental data, we suggest a mechanism of stress relaxation in strained (0001) InGaN/GaN layers, assuming formation of V-shaped edge-type dislocation half-loops. An energy-balance approach is applied to estimate the critical thickness of the InGaN layer resulting in generation of the V-shaped half-loops. The computed dependence of the critical thickness on the InGaN composition agrees well with the literature data reported for single-layer InGaN/GaN heterostructures.