It was noted that the imaging of extended defects at atomic resolution using high-resolution transmission electron micrography was problematic due to the lens aberrations of an uncorrected microscope and to the loss of phase during the recording of images. As a result, techniques to measure the strain fields of these defects could be applied only under distinct and well-controlled conditions sometimes in a narrow window of specimen thickness and imaging conditions. Using a combination of focal series reconstruction and numerically correction of the lens aberrations a posteriori allows overcoming these limitations. Also the strain fields could be measured by using geometrical phase analysis without further precautions. The application of these techniques to extended defects found in GaN was demonstrated. A discrepancy was discovered between the theoretically predicted structure of the Ga-terminated 90° partial and the experimentally observed one.

High Resolution Imaging of Extended Defects in GaN Using Wave Function Reconstruction. T.Niermann, M.Kocan, M.Roever, D.Mai, J.Malindretos, A.Rizzi, M.Seibt: Physica Status Solidi C, 2007, 4[8], 3010-4