Theory of Zener-photon resonances in the transport of two-band semiconductor superlattices

Using the density-matrix approach, we study intersubband tunnelling in supe rlattices subject to both de and ac electric fields aligned perpendicular t o the layers. Zener-photon resonances and dynamic localization are identifi ed both in the carrier occupation numbers and the current density. While a global, time-averaged population inversion cannot occur in the simple two-b and model considered, a temporal inversion is predicted to appear due to st rong ac fields in the THz range. At the Zener-photon resonances, the THz fi eld may generate appreciable gain.