The production of p-n junctions and polar transistors in silicon to small scale lengths maybe possible by plasma and electron beam techniques using the sub-threshold change of n-silicon into p-silicon by electron beam and its reversion at higher electron beam intensities. As a first step, in this study, experimental observation of the effect of electron beam on optical properties of n-type silicon samples is described. Electron bombardment with the energy of 20 keV and different doses in the range of 10(16) to 10(19) electron/cm(2) has been carried out. Use was made of a new design of an electron beam gun as described in details, using a helium obstructed discharge of a concave cold cathode. Optical properties of irradiated samples were determined by a UV-vis-NIR spectrophotometer. The results show an increase in the longer wave length than the fundamental band gap absorption with increasing electron dose. (C) 2004 Elsevier B.V. All rights reserved.