Probing Terahertz Dynamics in Semiconductor Nanostructures with the UCSB Free-electron Lasers

Non-linear electron dynamics in semiconductor nano-structures define a rich scientific arena with potential impact on novel devices in the terahertz regime, a relatively technology poor part of the spectrum. Experiments abound that explore the spectrum of collective and single particle excitations in nanostructures in the terahertz regime, but "real devices" are inevitably driven far-from equilibrium and there are few experiments that address non-linear dynamics in nanostructures. Here we describe two related experiments that attempt to address the terahertz dynamics of quantum transport in resonant tunneling structures. In the first, we determine the intrinsic relaxation time in resonant tunneling diodes by measuring the "rectified" response from 120 GHz to 3.9 THz. In the second, photon assisted tunneling is explored in sequential resonant tunneling superlattices. Finally, we return to resonant tunneling diodes and speculate on the prospects of recovering photon assisted tunneling and narrow band terahertz gain in resonant tunneling diodes.