Resonant-tunneling transfer times between asymmetric GaAs/${\mathrm{Al}}_{0.35}$${\mathrm{Ga}}_{0.65}$As double quantum wells

Electron tunneling through the barrier in asymmetric double-quantum-well structures is investigated by time-resolved picosecond luminescence spectroscopy. Change from nonresonant to resonant tunneling is acheived with a perpendicular electric field. Energetic alignment of electron subbands in the two wells strongly enhances tunneling transfer rates. The resonant transfer times decrease strongly with barrier thickness. The wells are coupled at resonance by energy-conserving scattering processes between states localized in a single well. The buildup of delocalized coherent states at resonance would lead to much shorter transfer times.