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New possibilities for magnetic domain studies are demonstrated using a combination of nonlinear magneto-optical microscopy and a conventional linear polarizing microscope. The use of an optical response that is governed by a higher rank tensor offers sensitivity to additional combinations of magnetization directions and optical wave vector and polarization, which is demonstrated in magnetic garnet films of different crystallographic orientations. We observed a nontrivial modulated domain structure in a (210) film and a clear domain contrast for a (111) film, where the linear image only indicated simple up–down domains and no domain contrast for these two situations, respectively.

A photoluminescence ͑PL͒ study of GaN homoepitaxial layers grown by metal-organic chemical-vapor deposition demonstrates the high optical quality of N-face layers deposited on vicinal (0001) GaN substrates. In contrast to broad PL emission in exact (0001) layers, narrow-bound ͑0.9 meV͒ and free-͑A and B͒ excitonic transitions are observed. By following the PL spectra as a function of temperature and excitation power, the main optical transitions in the Ga-and the misoriented N-face layers are found to be the same. Observed differences are related to the distinct creation of donor and acceptor states in the samples of different polarities.

We present a study on the material properties of GaN films grown on (111) silicon substrates by low-pressure metalorganic chemical vapour deposition using AlN buffer layers. This buffer layer is optimised with respect to growth temperature and time for the optical and structural properties of the GaN epilayers. The insertion of a Si x N y intermediate layer significantly increases the optical and structural properties. It results in a reduction of the D 0 X FWHM to 10 meV and in a 2.5-fold increase of its luminescence intensity. The FWHM of symmetric and asymmetric w-scans are reduced from 832 to 669 arcsec and from 702 to 547 arcsec, respectively.Introduction Despite difficulties in the growth of GaN on silicon, caused by a lattice mismatch of 17% and by thermal expansion coefficient incompatibility, silicon is considered to be one of the best candidates as an alternative, inexpensive and large substrate for depositing GaN. Future applications, like the integration of silicon based electronics with GaN opto-electronic devices, are the motivation for this research. Because GaN cannot be used as a buffer layer on Si(111) substrates due to wetting problems, we have investigated the use of AlN buffer layers. We have optimised the AlN buffer layer with respect to its thickness and growth temperature. The physical properties of MOCVD grown GaN epilayers (layer thicknesses %3 mm) on Si(111) substrates with these AlN buffer layers were investigated. Alternatively, we propose the insertion of a SiN intermediate layer after 1 mm of GaN growth. The results of this alternative approach will be compared with those obtained with the AlN buffer.

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