Slow contamination and fast surface state effects SEM studies of Si phototransistors

Abstract

The rate of growth of contamination films on the surface of Si phototransistors under examination in a scanning electron microscope was measured by multiple beam interferometry. The contamination film reduced the barrier electron voltaic effect current (i.e. the ″EBIC″ signal) by 10 to 20% after scanning a single line for an hour. The photovoltaic effect current of the transistors however was reduced by 90% after scanning the whole area of these devices for a few seconds. This is ascribed to the fact that bombardment-induced changes in surface electrical conditions strongly affect the carriers produced near the surface by photons but not the carriers produced at depths up to 2μm or more by the electron beam.