ABSTRACT
We have utilized tunneling spectroscopy to investigate the miniband structure of MBE-grown finite superlattice samples, and have observed for the first time the transition from a superlattice miniband to a tightly-coupled sequential well structure far below the Stark localization threshold. The transition from an indistinguishable miniband to a coupled well structure in these samples was experimentally found to be 2.5 meV < W(miniband width)/n(# periods) < 10.5 meV. By varying the number of periods until the individual eigenstates are no longer visible, the superlattice coherence length can be directly measured, which for these structures is ~1000A.
