Combined electron beam induced current and transmission electron microscopy ͑TEM͒ measurements have been performed on both undoped and Si-doped AlGaN epitaxial films with aluminum contents x ranging from xϭ0 to xϭ0.79, in order to correlate the electrical and structural properties of the films. The diffusion length of holes in the films ranges between 0.3 and 15.9 m, and the estimated lifetime of holes for doped samples varies between 0.2 ns and 16 s. Different effects contribute to the observed increase in the diffusion length with increasing aluminum content. Among others, dislocations seem to be active as nonradiative recombination sites, and phase separation and decomposition as observed by TEM in Al-rich alloys lead to the formation of a spatially indirect recombination path due to the piezoelectric field in the films. Potential fluctuations associated with these phase irregularities could also give rise to electron induced persistent conductivity contributing to the increase of the diffusion length. From our experimental observations, we conclude that the silicon dopants are partially activated in Al-rich alloys, and do not influence significantly the values of the diffusion length of holes in these samples.

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The grain boundary populations in laser crystallized polycrystalline silicon thin films are determined by electron microscope analysis, using electron backscattering contrast in the scanning electron microscope, and convergent beam electron diffraction in the transmission electron microscope. The grain boundary populations of the grains larger than 0.5 μm are dominated by first and second order twin boundaries. This result is found to be a general feature of laser crystallization independent of the experimental details of the laser crystallization process. Texture analysis of the laser crystallized poly-Si films shows that under certain experimental conditions a {111}-preferential orientation of the grains perpendicular to the substrate can be obtained.

We investigate the microstructure of polycrystalline silicon films (grain size, orientation distribution, and grain boundary population). These films are produced by laser crystallization of amorphous silicon on glass substrates by a frequency doubled Nd:YVO4 laser operating at a wavelength of 532 nm. Transmission electron microscopy reveals that the grains have an average width between 0.25 and 5 μm depending on the crystallization parameters and a length of several 10 μm. Electron backscattering diffraction experiments show that the grain orientation of the poly-Si films is textured. Type and extent of texture depend in a complex way on the thickness of the crystallized amorphous silicon layer, on the repetition rate of the laser pulses, and on whether or not an additional buffer layer is present on the glass substrate. In any case, the grain boundary population is dominated by first and second order twin boundaries.