INTERACTION OF WANNIER-STARK LEVELS IN A WIDE WELL SUPERLATTICE

We have investigated the energy spectrum of a superlattice with wide q uantum wells under the bias of an electric field perpendicular to the superlattice layers. By using photocurrent spectroscopy, transitions o f Wannier-Stark levels for the various electron and hole states are ob served, and at low fields, further structures corresponding to miniban d edge transitions are found. Various anticrossings could be observed at higher and lower electric fields. The anticrossings at high electri c fields are due to energy alignment of different electronic sublevels in adjacent wells. The anticrossing structures at low fields could be interpreted as resonances between intrawell and interwell excitonic W annier-Stark states with equal sublevel states, where the anticrossing is caused by differences in exciton binding energy. Fitting of transi tions and anticrossings was done by using a semi-empirical model and w e have extracted relevant fitting parameters like the quantum-confined Stark coefficient, binding energies for the excitonic Wannier-Stark l evels and the resonant coupling strength for states involved in the va rious anticrossing transitions. Finally, insight into the excitonic in fluences on the coupling of the WS states could be obtained by compari ng the fitted parameters for the various transitions. (C) 1998 Academi c Press.