Abstract
The primary aim of the work described in this thesis was to examine theoretically the interaction of an electron beam with commercially available silicon devices , originally intended as avalanche photodiodes and investigate experimentally the possible application of these photodiodes as electron-bombarded semiconductor targets. Theoretically the expressions for static and time-dependent current gains in silicon avalanche photodiodes under electron bombardment were derived from solutions of the diffusion equation and boundary conditions. These expressions have been presented also for estimating frequency limitations of these avalanche photodiode targets. The limiting factor of the high frequency response is shown to be limited by the n+ contact layer thickness. The current wave forms induced in the external circuit due to initial bombarding electrons have been derived and computed. Using capacitance-voltage curves measured at several frequencies, the characteristics of a number of silicon avalanche photodiodes, such as diode structure, doping profile, electric field profile, series resistance, depletion layer width, avalanche zone, ionization rates for electrons and holes, have been calculated. To perform the experimental investigations an electron bombardment apparatus was set up for bombarding the photodiode. A key component of this apparatus is a deflection system which deflects the electron beam to and from in front of the photodiode aperture at a very high speed. Experimental measurements have been obtained for the electron bombardment conductivity (EBC) of avalanche silicon photodiodes under controlled avalanching conditions using this apparatus. It was shown that the EBC gain and the avalanche multiplication of the diode can be cascaded. The current wave forms produced by initial bombarding electrons in the photodiodes were viewed on a sampling oscilloscope which has a rise-time of 28 picoseconds.