Evaluation of the infrared absorption in nm-thick heavily boron-doped Si1-xGex layers on silicon

Abstract

Infrared absorption due to free carriers was measured in the spectral range of 1.5–25 μm at 77 and 300 K on a large variety of heavily p-doped, p++=(2-7)×1020cm-3 strained Si1-xGex quantum wells on Si grown by molecular beam epitaxy (MBE). The validity of the commonly applied theoretical approaches to describe the spectra has been thoroughly analyzed. The well-known dependence α∝λ yielded by the Drude theory is not observed. Moreover, it is shown that the Boltzmann kinetic equation is invalid under our experimental conditions. The necessity of a new theory, where the interaction energy of carriers with scattering centers would be included into the energy spectrum of the system, is shown.