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A combined experimental and modeling study of stress and curvature evolution during (0001) GaN growth on (0001) 4H‐SiC wafers is presented. It is shown that the GaN layers are under the compressive stress, whose magnitude depends on the composition of the AlGaN buffer that is used to accommodate the epitaxial strain between GaN and SiC. Processing of in situcurvature measurements suggests fast relaxation of the mismatch stress in GaN when the Al content is increased. At that, nucleation of new dislocations is possible, but the dislocation density decreases rapidly over a narrow part of the GaN layer due to large inclination and annihilation of the threading dislocations. Eventually, correlations between the curvature/stress/dislocation evolution and AlGaN buffer composition can be established and optimal strategy for the growth of crack‐free structures can be suggested.

InGaN‐based monolithic multi‐color light emitting diodes (LEDs) are studied both experimentally and theoretically with the focus on factors controlling their emission spectra and efficiency. A number of LEDs with different designs of spacers separating active regions providing blue and green light emission is examined. Unexpected behavior of the multi‐color LED efficiency is explained in terms of a simple balance model, assuming some degradation of materials quality of the green active region grown on top of the blue one. Electrical properties of spacers separating different active regions in the multi‐color LED structures are identified as the major factor controlling the contributions of these active regions to the total emission spectrum. Correlations between the type and level of the spacer doping and the emission spectrum are found by simulations. Alternative ways of the spectral control by using polarization doping in the graded‐composition InGaN and AlGaN alloys used as the spacers are suggested. Color characteristics of blue/green dual‐wavelength LEDs are also measured and discussed, regarding their possible applications. This paper considers various aspects of monolithic dual‐wavelength blue/green LEDs, from growth and characterization of LED structures to both experimental and theoretical analysis of their operation. Major factors controlling their emission spectra and efficiency are thoroughly studied and discussed.

We report on the first observation of folded acoustic phonons in the Raman spectra of short‐period AlN/GaN superlattices (SLs). The values of longitudinal and transverse sound velocities along the [0001] direction of SL were estimated. It is shown that the SL period can be evaluated from Raman data with a good accuracy. Ab initiocalculations of the zone‐center phonons in (AlN)n(GaN)nSLs with the number of monolayer equal to n= 2,4,6 were performed. The frequencies of phonon modes were calculated and the mode displacement patterns have been established. The theoretical Raman spectra were simulated and compared with experimental ones. A strong sensitivity of A1(LO) phonons confined within the AlN layer to its thickness was revealed both experimentally and in calculations. This finding can be used for quantitative characterization of short‐period AlN/GaN SLs.

The first successful results of the application of multifractal analysis to a quantitative description of mosaic-structure peculiarities, that are typical of a GaN epitaxial layer with hexagonal modification grown on (0001) sapphire substrates, have been obtained. The characteristic size of the mosaic structure has been measured to be 200-800 nm. The direct dependence of mobility on the multifractal parameters (the Renyi dimension or the self-organization degree and the order-degree index) of the surface topology of the mosaic structure has been observed for all GaN layers investigated.