An accurate method for determining intrinsic optical absorption in indirect band gap semiconductors

A straightforward technique is presented for measuring the absorption coefficient of band-to-band optical transitions in indirect band gap semiconductors. The technique is useful in any injection range and involves measurement of the depth-resolved free-carrier absorption throughout the instant gradient of photoexcited e-h pairs. Optical measurements are performed in the perpendicular geometry with a spatial resolution of a few microns. The experiments in crystalline Si and in 4H SiC for near band edge excitation reveal a high measurement accuracy. An application of the technique to an extraction of dynamic or rigid band gap narrowing is briefly discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.