Out-of-focus observations of p–n junctions by high-voltage electron microscopy

The advantages in the use of high-voltage electron microscopy in the observation of reverse-biased p–n junctions are considered. Some theoretical results concerning the influence on the Fresnel image of the electric field inside the junction and of the external leakage field are presented for different values of the accelerating voltage. Preliminary experimental results obtained with a Hitachi microscope at the operating voltages ranging between 400 and 1000 kV are shown and compared with theoretical predictions. They indicate that the high voltage electron microscope may be a useful tool in investigating the internal electric field associated to the depletion layer of reverse-biased p–n junctions. The working conditions are reported and discussed.