Research and engineering applications of off-axis electron holography can be split into three main categories:
i) Correct microscope aberration to achieve high spatial resolution;
ii) Measure electric fields in materials at high spatial resolution;
iii) Measure magnetic fields at high spatial resolution.
Off-axis electron holography has been widely applied to characterize p-n junction specimens prepared using focused ion beam (FIB) technique. When there are no magnetic fields and diffraction contrast from the p-n junction, the change in phase of an electron as it passes through the specimen is given by, 
CE -- The interaction constant between the fast electrons and matter, dependent on the energy of the electron wave (e.g. 7.29 x 10−3 rad V−1 nm−1 for 200 kV electrons),
V -- The electrostatic potential, or called the mean inner potential (MIP in V).
t -- The local thickness of the specimen,
z -- The electron beam direction. 
Therefore, the phase of an electron is very sensitive to changes of dopant-induced potential in the specimens.
In order to optimize the acquisition of holograms, in many cases, the microscopes need to be re-configured. For instance, Cooper et al.  turned off the probe corrector in their FEG FEI Titan microscope even though it had been installed. Both the objective lens and third condenser lens were turned off, and a Lorentz lens was used in order to extend the holographic field of view to 1500 x 700 nm2. Consequently, the fringe spacing in the holograms was 3.5 nm, resulting in a spatial resolution of ~10 nm in the reconstructed phase images.
Figure 4305 shows examples of the phase images and cosine images of phases reconstructed from recorded holograms from p-n junctions at two different concentrations. The specimen thicknesses were ~400 nm determined by CBED. Two phenomena are very clear:
i) The p-n junctions in the phase images do not extend all the way to the specimen surface, especially for low dopant concentrations.
ii) The near-surface of p-doped region appears to be at the same negative potential as the n-doped layers in the junctions, due to surface charge.
Figure 4305. (a) Phase images and (b) Cosine images of their phases for p-n junctions with the different dopant concentrations.
Adapted from 
From Equation 4305a, we can know that the built-in potential Vbi in the p-n junction can be measured by, 
Note that for a FIB-prepared specimen, there is an electrically inactive layer on both surfaces so that t needs to be replaced by t-tinactive. Here tinactive is the total thickness of the inactive layers on both sides of the TEM specimen.
 W. D. Rau, P. Schwander, F. H. Baumann, W. Hoppner, and A. Ourmazd,
Phys. Rev. Lett. 82, 2614 (1999).
 David Cooper, Pierrette Rivallin, Jean-Michel Hartmann, Amal Chabli, and Rafal E. Dunin-Borkowski, Extending the detection limit of dopants for focused ion beam prepared semiconductor specimens examined by off-axis electron holography, Journal of Applied Physics, 106, 064506 (2009).