Strain state analysis of InGaN/GaN – sources of error and optimized imaging conditions

Transmission electron microscopy investigation of the chemical composition of Inx Ga1–x N/GaN layers by strain state analysis can lead to substantial artefacts. We evaluated simulated images in dependence of specimen thickness, specimen orientation and objective lens defocus. We observed that the measurement is in agreement with the true strain profile for certain conditions only. An analysis of error sources revealed that artefacts are mainly caused by a combination of delocalization and the composition dependence of the phases of the beams contributing to the image formation. The delocalization effect is minimized for interference of the undiffracted beam with one of the 000 ± 2 beams. The least chemical shift of the phases is obtained using the 000 + 2 beam and a strong excitation of 000 + 4. Images simulated for these conditions taking into account lattice plane bending and strain using finite‐element calculations revealed a good agreement of evaluated and true strain profiles. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)