Evidence from Spectral Emissometry for Conduction Intraband Transitions in the 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 microns. The wavelength at which the band peak, lambda ~~ 2.3 micron, shows a negligible dependence on temperature while the peak intensity increases with temperature presumably as a result of the increasing intrinsic carrier concentration. A similar absorption band was reported in direct absorption measurements by Spitzer and Fan at room temperature for n-type Si with extrinsic electron concentrations of 10 sup (14) to 10 sup (19) cm sup (- 3). No such structure was found in extrinsic p-type Si. Spitzer and Fan were unable to identify the mechanism for this anomalous absorption of free electrons in both experiments is due to intraband transitions in the conduction band from the DELTA sub 1 conduction band edge across an energy gap of E ~ 0.5eV to a higher lying DELTA sub 2' conduction band.