Off-axis acoustoelectric domains studied by Brillouin scattering

Abstract

An investigation is made of Brillouin scattering of acoustoelectric domains in semiconducting ZnO and CdS, in the case where the crystal is oriented with the electric drift field parallel to the hexagonal axis. The domains consist of off-axis shear waves. Angular dispersion due to strong elastic anisotropy is studied, and it is shown that the angle of maximum gain depends on the applied voltage and is limited by the sample geometry. The development of the angular spectrum for several acoustic frequencies is determined. The frequency spectrum of the domain is dominated by frequencies well below the frequency of maximum linear gain. Es wird die Brillouinstreuung von akustoelektrischen Domanen in halbleitendem ZnOund CdS fur den Fall untersucht, da13 die elektrische Feldstarke parallel zur hexagonalen Achse orientiert ist. Die Domanen bestehen aus transversalen ,,off-axis"-Wellen. Die Winkelverteilung der Energie in den anisotropen Kristallen wird beziiglich der Verteilung der Schallgeschwindigkeit der laufenden Domanen untersucht und gezeigt, da13 der Winkel fur maximale akustoelektrische Verstirkung vom angelegten elektrischen Feld und vom Querschnitt des Kristalls abhangt. Die Winkelverteilung verschiedener akustischer Frequenzen wurde untersucht und gefunden, daB Frequenzen dominieren, die betrachtlich kleiner als die Frequenz maximaler linearer Verstarkung sind.

Angular dispersion effects in the acoustoelectric interaction in ZnO and CdS

“…of phase propagation and the c-axis for the T2, T1, and L-modes in ZnO and CdS have been published by the author [6]. The result of these calculations is redrawn in Fig.…”

“…The first direct evidences for the involvement of off-axis waves were obtained about five years later by studying light scattering from acoustic domains [2] and by investigating the local change in birefringence induced by the strain accompanying the acoustic flux [3]. In connection with these measurements the linear theory of acoustic amplification [a] was extended by Klein [6] to account for the elastic and piezoelectric anisotropy.…”

“…I n the following years Brillouin-scattering technique has turned out to be a unique probe for testing Klein's theory and some of its consequences [6]. The main reason for this is that the angel-dependent gain occurring in the modified linear theory applies to the plane wave components in the acoustoelectric domain, and these can be directly investigated by Brillouin scattering, since the Bragg condition is equivalent to constructive interference from planes of constant phase.…”