Evidence from spectral emissometry for conduction intraband transitions inthe intrinsic regime for silicon

From emissometry measurements in lightly doped Si at elevated temperatures, we have observed an anomalous absorption band in the wavelength range of 1 -5 mu m. The wavelength at which the band peaks, lambda approximate to 2.3 mu m, shows a negligible dependence on temperature while the peak intensity increases with temperature presumably as a result of the increasing intrin sic carrier concentration. Spitzer and Fan reported a similar absorption ba nd in direct absorption measurements at room temperature for n-type Si with extrinsic electron concentrations of 10(14) to 10(19)cm(-3). No such struc ture was found in extrinsic p-type Si. Spitzer and Fan were unable to ident ify the mechanism for this anomalous absorption. In both the experiments, t his absorption of free electrons is due to intraband transitions in the con duction band from the Delta(1) conduction band edge across an energy gap of E similar to 0.5 eV to a higher lying Delta(2)' conduction band.