Free carrier optical absorption at 10.6 μm in GaAs

Optical absorption measurements at 10.6 μm have been perfor-med in chromium doped GaAs samples using a calorimetric tech-nique at 300 K, and an optical system to determine the varia-tion of the absorption versus temperature between 300 K and 650 K. Hall effect measurements have also been carried out in the same temperature range. The optical absorption cross sec-tion for both electrons and holes are discussed and experi-mentally determined. A semi-empirical formula is deduced which permit the calculation of the 10.6 μm free carrier absorption at any temperature and doping level provided the electron mobility is known. Besides free carrier and multi-phonon absorption another mechanism must be considered to explain the experimental data. Possible effect of small pre-cipitates is discussed.