The propagation of ultrasonic waves in piezoelectric semiconductors

The equations of wave propagation in piezoelectric semiconductors have been derived for a frame of reference in which the principal axes concide with the crystallographic axes. It is shown that generally the dispersion relation is given by a determinant of order six but under condition wherein the plasma modes are not excited, it could be reduced to a determinant of order five, which is equivalent to the one given by Hutson and White. The dispersion relation for hybrid waves which couple acoustic phonons with plasmons has been derived and this is shown to be given by a determinental equation of order four.