Energy-filtered transmission electron microscopy of multilayers in semiconductors

Quantitative analysis of novel semiconductors with wide or ultrathin multil ayers of atomic dimensions is very important in order to control electronic and optical properties. but rather difficult due to the limited resolution in most techniques. In this paper we attempt to assess how effectively the total As dopant concentration in ultrathin As doped layers in InP and the Ti atomic fraction in a TixAl1-xN multilayer can be analysed quantitatively using energy-filtered imaging. These two materials have characteristic edg es located at widely different energy losses, with the L edge of:is being a bove 1000 eV, while that of Ti is around 450 eV. We have quantified the As concentration using the three-window technique and theoretical cross-sectio ns and we find that the resolution limit is dominated by the signal-to-nois e ratio in this delta-doped specimen. However, the accuracy of the Ti atomi c fraction in TixAl1-xN can be as good as 10 at% for specimens of uniform t hickness made by focused ion beam milling, We will compare our results with measurements of the composition made using Fresnel contrast, high resoluti on imaging and high angle annular dark field techniques.