Photon-assisted transport is shown to be a remarkably robust phenomeno
n in sequential resonant superlattices with a large energy separation
between the ground state and the first excited state of the quantum we
lls. Photon-assisted tunneling involving up to seven photons per tunne
ling event, stands out very clearly. The one-photon channel is observe
d up to 300 K. This implies that these superlattices are a gain medium
at THz frequencies even at room temperature and potentially important
for the future design of THz sources. (C) 1996 American Institute of
Physics.