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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 situ curvature 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present a method for determining the diffusion lengths of Ga adatoms on GaN by combining profiling of the tops of GaN stripes obtained by selective area MOCVD and a diffusion growth model. We deduce very high values of the diffusion lengths on tops of <11-20>-oriented stripes at 1040 °C which range from 6 μm under nitrogen-rich to 24 μm under hydrogen-rich atmosphere in the reactor. The obtained results show in particular that Ga-catalyzed growth of GaN nanostructures and nanowires should not be limited by Ga influx and thus the exceptional growth rate is anticipated in such cases. [ABSTRACT FROM AUTHOR]