Measurement of energy loss from a HEMT structure by observing emitted phonons

Using nanosecond heat pulse techniques the authors 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 the authors 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+or-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.