Quantum tunability of superlattice minibands.

Abstract

We show that it is possible to control the gap between the minibands of a conventional superlattice by introducing positive potential barriers in its wells or potential wells in its barriers. An appropriate choice of the position, the width d, and the height ${\mathit{V}}_{\mathit{d}}$ (depth ${\mathit{V}}_{\mathit{c}}$) of these barriers (wells), achieved by standard methods, can reduce the energy minigaps to the desired values. When these barriers are introduced at the center of the wells of the original structure, the position of the second miniband ${\mathit{E}}_{2}$ in energy space changes very little with d and/or ${\mathit{V}}_{\mathit{d}}$ whereas that of the first miniband ${\mathit{E}}_{1}$ can change by 1 to 2 orders of magnitude. This leads to a tuning of the first miniband and of the gap ${\mathit{E}}_{2}$-${\mathit{E}}_{1}$ and is in sharp contrast with conventional structures where both ${\mathit{E}}_{1}$ and ${\mathit{E}}_{2}$ change and a control over both the width and the height of the barriers is necessary for band-gap tuning. Similar results are obtained for the case of wells in the barriers. Possible applications include infrared photodetectors and tuning of the tunneling current.