Resonant tunneling processes in an asymmetric X-band double quantum well structure

Resonant tunneling processes in an asymmetric X-band double quantum well are investigated. In reverse bias where the transverse X state, X_XY(1), with a lighter tunneling mass is the emitter state, a clear X-resonance peak with a large peak-to-valley ratio (PVR) is observed, followed by its TO-phonon-assisted resonances. Qualitative assignment of the observed resonances is validated by using a self-consistent band profile calculations which are achieved by numerically solving the Schrödinger-Poisson equations. On the other hand, comparable peaks in forward bias where the emitter state is a longitudinal X state, X_Z(1), with a heavier mass are not observed, but up to four phonon-assisted resonant tunneling processes are detected. The built-in electric field at zero bias is taken into account to qualitatively support the assignments.