Infrared Absorption in Heavily Doped n‐Type Si

Abstract Transmission measurements are reported on highly phosphorous‐doped n‐type Si, at three different temperatures 300, 85, and 35°K, and for carrier densities ranging from 6 × 10 18 to 4.9 × 10 20 cm −3 . Below the fundamental energy gap, the data are analysed in terms of three different processes: free carrier absorption, indirect transitions including the phonon contribution as well as the impurity or electron—electron scattering, and interconduction‐band transitions. The absorption band due to inter‐conduction‐band transitions is observed to shift to higher wavelengths, when the doping increases. An explanation is given, taking into account the rise of the Fermi level in the conduction band.