INTERSUBBAND ABSORPTION IN MODULATION-DOPED P-TYPE SI1-XGEX QUANTUM-WELLS - THEORY AND EXPERIMENT

A study of intersubband infrared absorption in modulation doped p-type Si/SiGe quantum wells is presented for SiGe wells with thicknesses be tween 22 Angstrom and 64 Angstrom, and Ge contents in the range from 2 3 % to 58 %. The peak positions of the absorption lines are observed b etween 500 cm(-1) and 2200 cm(-1). Depending on the barrier height (i. e., on the Ge content of the wells), the heavy-hole states excited by the infrared radiation are either localized in the wells or strongly m ixed with barrier-bound states and therefore delocalized. The shape of the absorption line correspondingly changes from a narrow Lorentz lin e to a rather broad absorption band. Using the structural parameters d etermined by high-resolution triple-axis x-ray diffraction, the result s of a self-consistent Luttinger-Kohn type envelope function approach with the explicit inclusion of the strain in the quantum wells are in excellent agreement with the measured spectra.