The local electric behaviour of IMPATT diodes was studied by scanning
transmission electron beam induced current in cross-section method
(X-STEBIC). This technique of induced current measurement makes it possible
to probe the depletion zone of a junction with the beam of a transmission
electron microscope. Two series of experiments were carried out. The
X-STEBIC signal was analyzed according to the sample thickness and under
different electrical polarizations. Moreover, these measurements were done
and compared at room and low temperature (≅110 K). From these data,
simulations of X-STEBIC profile allowed us to determine the main physical
parameters brought into play in the signal formation. We have shown that, in
the vicinity of the junction, the intensity of the induced current partly
depends on the avalanche effect. The kinetic energy of the minority carriers
generated by the electron beam is sufficient to induce collisions in
cascade, even when the junction is not polarized. At low temperature,
surface recombination has an essential role on the lateral resolution of the
X-STEBIC method. By choosing carefully the range of sample thickness and by
positioning the probe in the field of the diode, it is possible to optimize
the resolution. Surface recombination annihilates the diffusion of the
carriers so that the STEBIC image becomes a true image of the electric
field. Consequently, semi-quantitative physical data can be obtained on the
junction field.