title: Strain measurement in semiconductor heterostructures by scanning transmission electron microscopy.
abstract: This article deals with the measurement of strain in semiconductor heterostructures from convergent beam electron diffraction patterns. In particular, three different algorithms in the field of (circular) pattern recognition are presented that are able to detect diffracted disc positions accurately, from which the strain in growth direction is calculated. Although the three approaches are very different as one is based on edge detection, one on rotational averages, and one on cross correlation with masks, it is found that identical strain profiles result for an In                  x               Ga1-x               N                  y               As1-y               /GaAs heterostructure consisting of five compressively and tensile strained layers. We achieve a precision of strain measurements of 7-9·10-4 and a spatial resolution of 0.5-0.7 nm over the whole width of the layer stack which was 350 nm. Being already very applicable to strain measurements in contemporary nanostructures, we additionally suggest future hardware and software designs optimized for fast and direct acquisition of strain distributions, motivated by the present studies.
authors.affiliation: Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany. mueller@ifp.uni-bremen.de
authors.forename: Knut
authors.initials: K
authors.lastname: Müller
authors.forename: Andreas
authors.initials: A
authors.lastname: Rosenauer
authors.forename: Marco
authors.initials: M
authors.lastname: Schowalter
authors.forename: Josef
authors.initials: J
authors.lastname: Zweck
authors.forename: Rafael
authors.initials: R
authors.lastname: Fritz
authors.forename: Kerstin
authors.initials: K
authors.lastname: Volz