PHONON EMISSION BY HOT-ELECTRONS IN DELTA-DOPED GAAS

Simultaneous measurements of current-voltage characteristics and time-of-flight spectra of emitted phonons were performed for delta-doped GaAs at 2 K. The phonon flux consists of two parts: a narrow signal due to the ballistic arrival of the acoustic phonons and a broad signal arising from the decay products of optical phonons emitted by hot electrons. An increase in conductivity and a decrease in the time-integrated narrow signal divided by the input power are observed at moderate field strengths. Both features are explained by the real-space transfer of electrons from the quantum wells to extended states. At high fields the conductivity decreases whereas both phonon fluxes per input power increase. These effects are suggested to be due to the transfer of hot electrons from the GAMMA band edge to the L valleys assisted by the deformation potential interaction with phonons. The dependence of the position of the maximum of the narrow signal on the duration of the voltage pulses at constant input energy indicates the presence of inelastic phonon-phonon interactions and the formation of the hot spot.