INTERACTION OF SURFACE ACOUSTIC WAVES, ELECTRONS, AND LIGHT

Abstract

The interaction of surface acoustic waves with free carriers in semiconductor nanostructures has turned out to yield a powerful tool not only for the investigation of the dynamic conductivity of such quantum systems. The latter has been shown in the study of the dynamics of the fractional and integer quantum Hall effect and many other interesting physical phenomena. The interaction is based on a relaxation type and impedance matching effect. However - to make practical use of this strong interaction, the electromechanical coupling coefficients of state-of-the-art semiconductor layered systems are too small. A hybrid technique, merging the strong piezoelectricity of LiNbO 3 or similar substrates with the excellent electronic properties of band gap engineered semiconductor quantum wells tackles this problem. Based on this new hybridization technique, several acoustoelectric high frequency devices have been realized. But also optically generated free electrons and holes in a semiconductor efficiently interact with the piezoelectric fields and potentials accompanying the surface wave. Those are able to field-ionize optically generated excitons leading to an acoustically induced quenching of the photoluminescence of a semiconductor quantum well, and to a system in which photonic signals can be efficiently converted into spatially separated electrons and holes which then can be transported over macroscopic distances along the quantum well. Finally - at a predetermined time and location on the sample – they can be reassembled into photonic signals. But also much simpler photonic devices can be realized using surface acoustic waves on semiconductor samples. For instance, we report on a simple, yet efficient camera type of device for pattern recognition and image processing.