MINIBANDS IN THE CONTINUUM OF MULTI-QUANTUM-WELL SUPERLATTICES

We report the first observation of well defined minibands and minigaps between them, at energies above the barriers in multi-quantum-well st ructures. Using intersubband absorption spectroscopy, we have observed the optical transitions between confined electronic states of isolate d quantum wells to minibands in the continuum of the periodic structur e. By comparison with a theoretical model we spectroscopically identif y all the observed transitions and explain their strength and spectral shape. In addition, we estimate the coherence length of the electroni c wave function in these minibands comparing the absorption spectrum w ith that of a finite array of quantum wells.