Improved Light Absorption by Quantum Confinement and Band Folding:   Enhanced Efficiency in Silicon Based Solar Cells
  The improvement of light absorption in Si/BeSe$_{0.41}$Te$_{0.59}$ heterostructures for solar cell applications is studied theoretically. First, using simple approaches we found that light absorption could be improved in a single (uncoupled) quantum well with a thickness up to 20 {\AA}. Second, by semiempirical tight-binding methods we calculated the electronic structure and optical properties of various (Si$_{2})_{n}$/(BeSe$_{0.41}$Te$_{0.59})_{m}$ [001] superlattices. Two bands of interface states were found in the band gap of bulk Si. Our calculations indicate that the optical edges are close to the fundamental band gap of bulk Si and the transitions are optically allowed. 
T. Sandu and W. P. Kirk