Ultrafast intersubband scattering of holes in p-type modulation-doped Si1−xGex/Si multiple quantum wells

We report on an experimental and theoretical study of intersubband relaxation of holes in p-type modulation-doped Si1−xGex/Si multiple quantum wells. The ultrafast hole dynamics is studied in pump–probe experiments with View the MathML source mid-infrared pulses. For View the MathML source wide wells (x=0.5) the lifetime of holes in the second heavy hole subband is only View the MathML source due to rapid emission of optical phonons via the deformation potential interaction. Model calculations of hole–phonon scattering give an almost identical value and point to the crucial role of cascaded scattering via an intermediate subband with light-hole-split-off symmetry.