Direct comparison of off-axis holography and differential phase contrast for the mapping of electric fields in semiconductors by transmission electron microscopy.

To provide a direct comparison, off-axis holography and differential phase contrast have been performed using the same microscope on the same specimens for the measurement of active dopants and piezoelectric fields. The sensitivity and spatial resolution of the two techniques have been assessed through the study of a simple silicon p-n junction observed at different bias voltages applied in-situ. For an evaluation of limitations and artefacts of the methods in more complicated systems a silicon pMOS device and an InGaN/GaN superlattice with 2.2-nm In0.15Ga0.85N quantum wells is investigated. We demonstrate the effects of dynamical scattering on the electric field measurements in the presence of local strain-induced sample tilts and its dependence on parameters like the convergence angle.