Photon induced far-infrared absorption in pure single crystal silicon

Illumination of silicon by direct sunlight was found to cause a significant increase in the far-infrared (FIR) absorption of silicon. The effect was o bserved during a recent measurement campaign using a 2.5 THz airborne heter odyne spectrometer for atmospheric measurements together with a silicon air craft window. In this work, the absorption increase was reproduced in the l aboratory by illumination of a silicon sample with a halogen lamp. The anal ysis of the energy flux dependence and the wavenumber dependence support th e assumption that the increased absorption in the FIR is due to photon indu ced transitions of electrons from the Valence band to the conduction band. This effect might be of importance to a number of instruments using silicon components. (C) 1999 Elsevier Science B.V. All rights reserved.