EMISSION AND ABSORPTION OF PHONONS BY THE 2-DIMENSIONAL ELECTRON-GAS IN A GAAS MODFET STRUCTURE

We have observed both emission and absorption of phonons by the two-dimensional electron gas in a GaAs modulation-doped field effect transistor (MODFET). For the first time in this system directly emitted LA phonons were seen, in addition to the TA products of LO down-conversion. The angular dependence of the LA feature suggested that its origin was piezoelectric not deformation potential coupling. Direct absorption of phonons by the 2DEG was found to have a response time approximately ns, so that the transmission stop bands of a superlattice phonon filter could be used as a dispersive spectrometer

MEASUREMENT OF ENERGY-LOSS FROM A HEMT STRUCTURE BY OBSERVING EMITTED PHONONS

Using nanosecond heat pulse techniques we have observed both acoustic and optic phonon emission by the hot 2DEG in GaAs/AlGaAs HEMT structures. Both transverse and longitudinal modes were detected in the optic regime but only transverse in the acoustic regime. The ability to vary carrier density allowed us to eliminate the effect of contact resistance and hence to determine absolutely the power level at which energy loss took place equally via acoustic and optic phonons. The figure obtained was 2.3 +/- 0.5 pW per electron, inconsistent with a model of acoustic emission based simply on deformation potential coupling, suggesting the presence of an additional source of inelastic scattering