PHONON EMISSION BY HOT 2-DIMENSIONAL ELECTRONS IN GALLIUM-ARSENIDE DEVICES - THE MYSTERY OF THE MISSING LONGITUDINAL MODE

A peculiar feature of the phonon emission by a warm two-dimensional el ectron gas (2DEG) in a gallium-arsenide (GaAs) heterojunction is that, compared with tile transverse acoustic (TA) mode. emission of the lon gitudinal acoustic (LA) mode is very weak, In bulk GaAs, LA emission i s much stronger because the LA mode couples to electrons in GaAs as th e deformation potential (DP) whereas the TA does not. One possible rea son for the anomaly is that in a 2DEG, owing to the reduction in phase space for electron scattering, the electron-phonon interaction is cut off at small wavevector, q, before DP coupling (proportional to q) ca n dominate over piezoelectric (PE) coupling (proportional to q(-1)).