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

Infrared absorption due to free carriers was measured in the spectral range of 1.5-25 mum at 77 and 300 K on a large variety of heavily p-doped, p(++) = (2-7) x 10(20)cm(-3) strained Si1-xGex quantum wells on Si grown by mole cular beam epitaxy (MBE). The validity of the commonly applied theoretical approaches to describe the spectra has been thoroughly analyzed. The well-k nown dependence alpha proportional to lambda (2) yielded by the Drude theor y is not observed. Moreover, it is shown that the Boltzmann kinetic equatio n is invalid under our experimental conditions. The necessity of a new theo ry, where the interaction energy of carriers with scattering centers would be included into the energy spectrum of the system, is shown. (C) 2001 Kluw er Academic Publishers.