Raman-spectroscopy investigations of photoinduced changes of the spatial charge-carrier distribution in p-type modulation-doped quantum-well structures

We have investigated the consequences of photoinduced changes of the spatial distribution of charge carriers in p-type modulation-doped GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As–multiple-quantum-well structures on the Raman spectra of hole intersubband excitations as well as of electronic excitations with energies below the smallest quantum- well subband spacings, called low-energy excitations (LEEX). The dynamical process of the hole redistribution after pulsed illumination became obvious in variations of the position, intensity, and line shape of the Raman signals as a function of the delay time between sample illumination and signal detection. The observed modifications of the hole intersubband transitions are due to changes of the width of the single-particle spectrum and of the strength of many-particle interaction effects as well as due to a reduced Coulomb scattering by ionized impurity atoms in the barriers. Referring to the LEEX signals a scattering process is proposed which involves transitions between quantized states in the center regions of the barriers. © 1996 The American Physical Society.