Quantitative analysis of ultrathin doping layers in semiconductors using high-angle annular dark field images

It is well known that the high-angle annular darli field (HAADF technique i n scanning transmission electron microscopy is an incoherent imaging proces s in the lateral try) plane. However, as a consequence of the existence of partial coherence in the z direction, accurate quantitative interpretation of image intensity is difficult. The effects of coherence in the z directio n can be reduced by increasing the inner collector angle of the annular det ector so that the scattering from atoms in the z direction is essentially i ncoherent, We thus show that it is feasible to quantify the total As concen tration of ultrathin InAsxP1-x layers in InP in a simple but accurate way u sing a thickness integrated Bloch wave calculation including phonon scatter ing with a large inner collector angle of the annular detector of around 15 0 mrad. We compare the As composition derived from this approach with that from the Fresnel method and high resolution imaging, We also show that the non-linear variation of the HAADF intensity with thickness is consistent wi th our simpler simulations for such conditions. Therefore, this approach en ables us easily and quickly to quantify compositions using HAADF images. Th e tetragonal distortion due to lattice mismatch is also shown to influence the contrast and has been included in the calculations.