Photostimulated impurity absorption of ultrasound in semiconductor nanostructures

The problem of attenuation of ultrasound in a semiconductor with a quantum well structure with infinite potential barriers is tackled for the case in which the acoustic lattice vibrations interact with impurity centers in the presence of an exciting laser field. The electron transitions from an acceptor-impurity “band” to the first quantized energy level of the conduction band, forbidden in the absence of the laser field for the absorption of an acoustic wave quantum, become permitted in the presence of the external high frequency field. The external laser field will then supply the energy deficit for the electron to make the transition to absorb the acoustic phonon. The total ultrasound absorption coefficient αT was calculated using second-order perturbation theory and the result was specialized for the case of a GaAs/AlGaAs quantum well sample. It was found that αT is a fairly large quantity as compared with its value in bulk as the well width decreases from values corresponding to the almost bulk situation.