Biperiodic superlattices and the transparent state

We study biperiodic semiconductor superlattices, which consist of alternating cell types, one with wide wells and the other narrow wells, separated by equal strength barriers. If the wells were identical, it would be a simply periodic system of N=2n half-cells. When asymmetry is introduced, an allowed band splits at the Bragg point into two disjoint allowed bands. The Bragg resonance turns into a transparent state located close to the band edge of the lower (upper) band when the first (second) well is the wider. Analysis of this system gives insight into how band splitting occurs. Further, we consider semiperiodic systems having N=2n+1 half-cells. Surprisingly, these have very different transmission properties, with an envelope of transmission maxima, which crosses the envelope of minima at the transparent point.