We investigate the specifics of trigonal materials and their heterostructures, in particular alpha-phase (corundum phase) alumina and gallia and their alloy alpha-(Al,Ga)2O3. Compared to more common hexagonal semiconductor materials (like group-III nitrides), the symmetry is reduced. Regarding the elastic properties, this leads to the occurrence of shear strains in heteroepitaxy and a difference between a- and m-planes. Particular care must be taken when evaluating Raman scattering for the determination of the Raman tensor; for thin films, also the thickness must be taken into account. Also results on electrical properties will be given.
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