We investigated the relaxation behavior of InGaN/GaN blue multiple quantum wells (MQWs) grown on Si (111) and sapphire (0001) substrates to determine how the threading dislocation density (TDD) in the underlying GaN layer, the thickness of the MQWs, and the growth substrate (Si or sapphire) affect the relaxation behavior of MQWs. The results demonstrate that the value of the in-plane lattice parameter difference between MQWs and GaN (IPLD MQWs-GaN ) is strongly dependent on the TDD in the underlying GaN layer. The thickness of the InGaN well layer has the greatest effect on the IPLD MQWs-GaN value of the blue MQW structure: a thin InGaN well layer with high In content is more effective than a thick InGaN well layer with low In content for obtaining highquality blue MQWs without misfit dislocations (MDs). Furthermore, MQWs grown on Si are likely to contain MDs and unlikely to form V-defects, whereas the opposite tendency is true of MQWs grown on sapphire. Using threading dislocations, MDs, and V-defects, we propose relaxation mechanisms for MQWs grown on Si (111) and sapphire (0001) substrates.

We have studied microphotoluminescence mapping of InGaN quantum wells grown on GaN (0001) substrates with misorientation toward [1$/bar 1$00] direction. The fluctuation of peak energy and full width at half maximum in the mapping was large when the misorientation angle was 0.0° or 0.1°, whereas it was small when the misorientation angle was over 0.2°. The average of the full width at half maximum of InGaN peak had the minimum of below60 meV at room temperature when the misorientation angle was around 0.28°. These results indicate that InGaN quantum wells have high crystalline quality when grown on GaN (0001) substrates with misorientation angle between 0.2° and 0.3° toward [1$/bar 1$00] direction. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

We have successfully realized a very smooth surface morphology of GaN-based epitaxial layers on n-GaN (0001) substrates with the misorientation angle of approximately 0.2• only toward [1100] direction, which is confirmed using Nomarski microscopy and atomic force microscopy. In x-ray diffraction spectra, the narrow width of the satellite peak of superlattices also indicated the smooth surface morphology and abrupt interfaces of the epitaxial layers on the GaN (0001) substrate with the misorientation angle only toward [1100] direction. The realization of smooth surface morphology of the layers grown on GaN (0001) substrates misoriented only towards [1100] direction is considered to be closely related to the anisotropic inplane growth rate.

No abstract

No abstract