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GaN films implanted with Mg and Be ions were studied for optical and structural characteristics. Annealed Mg implanted GaN showed low temperature photoluminescence (PL) spectra of 356 nm near band edge emission, and a 528 nm green band deep level emission. The 528 nm green band emission may be attributed to the Mg implantation induced clustering defect.

An extensive Monte Carlo (MC) simulation is performed to investigate exchange bias in a novel model of a nanoparticle consisting of a ferromagnetic (FM) core and an amorphous magnetic (AM) shell. The magnetic glassy ordering of the AM shell governed by random magnetic anisotropy (RMA) is shown to be responsible for the unidirectional anisotropy to the FM core. Our MC results show that, while the bias field and coercivity exhibit a strong dependence on RMA strength, which looks like that on the antiferromagnetic (AFM) thickness in traditional FM/AFM bilayers, they are independent of AM thickness. However, the bias field and coercivity abruptly change with increasing small core size and get saturated for a large enough core size. The cooling field and temperature dependencies show the peculiar sign inversion of the bias field. Our study supports the argument that the exchange bias observed in some magnetic nanoparticles or nanocrystallined alloys is not necessarily due to the presence of an AFM phase. [ABSTRACT FROM AUTHOR]

The defect reduction in a wurtize GaN thin film with a multiple composite layer grown by atmospheric pressure organometallic vapor phase epitaxy on sapphire substrate is examined by using a cross -section transmission electron microscopy. The observations indicate that the multiple composite layer structure significantly reduces the density of threading dislocation generated from the GaN/Al(sub 2)O(sub 3) interface.