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Bulk ZnO samples, epitaxially grown ZnO layers, and ZnO nanostructures frequently exhibit a characteristic emission band at 3.31-eV photon energy whose origin is controversially discussed in the literature. Partly, this omnipresent band is ascribed to ͑e , A 0 ͒ transitions of conduction band electrons to acceptors, which are abundant in relatively high concentrations but have not positively been identified. The band is, in particular, often reported after intentional p-type doping of ZnO, preferentially with group V species. In the present work, we study the 3.31-eV band by low-temperature cathodoluminescence ͑CL͒ with high spatial resolution, by scanning electron microscopy, and by transmission electron microscopy ͑TEM͒. Line shape analyses at different temperatures give clear evidence that the band originates from an ͑e , A 0 ͒ transition where the acceptor binding energy is ͑130Ϯ 3͒ meV. The 3.31-eV luminescence is exclusively emitted from distinct lines on sample surfaces and cross sections representing intersections with basal planes of the wurtzite hexagons. Correlating monochromatic CL images with TEM images, we conclude that the localized acceptor states causing the 3.31-eV luminescence are located in basal plane stacking faults.

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Raman measurements were performed on molecular beam epitaxially grown GaN before and after implantation with Ar+, Mg+, P+, C+, and Ca+ ions. With increasing ion dose, new Raman peaks arise at 300, 360, 420, and 670 cm−1, independent of the ion species. After rapid thermal annealing at temperatures between 900 and 1150 °C for 15 s, the intensities of the Raman modes decrease with increasing temperature with the exception of the 360 cm−1 mode which shows a maximum in intensity after annealing at 900 °C. The mode at 300 cm−1 is attributed to disorder-activated Raman scattering, whereas the other three modes are assigned to local vibrations of vacancy-related defects.

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General expressions for the longitudinal and transverse resistivities of single-crystalline cubic and tetragonal ferromagnets are derived from a series expansion of the resistivity tensor with respect to the magnetization orientation. They are applied to strained (Ga,Mn)As films, grown on (001)-and (113)A-oriented GaAs substrates, where the resistivities are theoretically and experimentally studied for magnetic fields rotated within various planes parallel and perpendicular to the sample surface. We are able to model the measured angular dependences of the resistivities within the framework of a single ferromagnetic domain, calculating the field-dependent orientation of the magnetization by numerically minimizing the free-enthalpy density. Angle-dependent magnetotransport measurements are shown to be a powerful tool for probing both anisotropic magnetoresistance and magnetic anisotropy. The anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport measurements agree with those obtained by ferromagnetic resonance measurements within a factor of two.

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