NONEQUILIBRIUM OPTICAL-PHONON POPULATION BY SEQUENTIAL RESONANT-TUNNELING IN GAAS-ALAS SUPERLATTICES

We report on the observation of nonequilibrium GaAs LO phonons generat ed by the relaxation of hot electrons due to sequential resonant tunne ling in strongly coupled superlattices. Raman-scattering experiments w ere performed at 5 K with low optical excitation density. The anti-Sto kes LO-phonon intensity, which gives a measure of the nonequilibrium L O-phonon population, exhibits maxima at the resonant tunneling voltage s. The transport data show that the electrical heating power increases linearly with voltage. Our results suggest that hot-electron cooling via acoustical phonon emission is suppressed under sequential resonant tunneling conditions.