Stimulated phonon emission in superlattices

We present the first study of the effect of ballistic acoustic phonons gene rated by a heated metal film on the tunnel current in GaAs/AlAs superlattic es. The phonon-induced increase of the tunnel current as a function of appl ied voltage has a maximum at a voltage which varies linearly with heater te mperature both in zero and applied magnetic held. The behaviour is consiste nt with phonon-assisted tunnelling by stimulated phonon emission. The syste m acts as a phonon spectrometer in the equal to or less than 1 THz frequenc y region with a resolution of approximately 200 GHz. (C) 1999 Elsevier Scie nce B.V. All rights reserved.