Low temperature (200–600°C) annealing in the transmission electron microscope (TEM) is used to provide a significant noise reduction in phase images of focused-ion-beam-milled GaAs and Si p-n junctions recorded using off-axis electron holography, as well as increasing the measured phase shifts across the junctions. Our results suggest that annealing removes defects resulting from Ga+ implantation and reactivates dopant atoms in the thin TEM specimens. In GaAs, electrically inactive surface layer thicknesses are reduced from 80to17nm on each specimen surface after annealing at 500°C. In Si the improvement is from 25to5nm.

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The measurement of potentials associated with dopant atoms in semiconductors at nanometer spatial resolution using off-axis electron holography is known to be affected by the presence of the surfaces of thin specimens. In particular, the potential across a p-n junction is often found to be lower than would be expected from predicted properties of bulk devices. Here we present simulations of two-dimensional potential profiles within a thin (<1 µm) parallel-sided specimen containing a p-n junction. We find that the potential across the p-n junction is always smaller, when projected through the specimen, than would be expected from the properties of the bulk material. Crucially, the step in potential across the junction is independent of the value of the potential on the surface of the specimen for high dopant concentrations (>1017 cm−3). The simulations are compared with experimental data. Although they can account for some of the reduction in the observed potential, they do not fully explain the experimental results.

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