PHOTOSTIMULATED IMPURITY ABSORPTION OF ULTRASOUND IN SEMICONDUCTOR NANOSTRUCTURES

The problem of attenuation of ultrasound in a semiconductor with a qua ntum well structure with infinite potential barriers is tackled for th e case in which the acoustic lattice vibrations interact with impurity centers in the presence of an exciting laser field. The electron tran sitions from an acceptor-impurity ''band'' to the first quantized ener gy level of the conduction band, forbidden in the absence of the laser field for the absorption of an acoustic wave quantum? become permitte d in the presence of the external high frequency field. The external l aser field will then supply the energy deficit for the electron to mak e the transition to absorb the acoustic phonon. The total ultrasound a bsorption coefficient alpha(T) was calculated using second-order pertu rbation theory and the result was specialized for the case of a GaAs/A lGaAs quantum well sample. It was found that alpha(T) is a fairly larg e quantity as compared with its value in bulk as the well width decrea ses from values corresponding to the almost bulk situation. (C) 1998 A merican Institute of Physics. [S0021-8979(98)04217-0].