Electric-field-dependent absorption of ZnSe-based quantum wells: The transition from two-dimensional to three-dimensional behavior

The absorption coefficient of ${\mathrm{Zn}}_x{\mathrm{Cd}}_{1-x}{\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}\mathrm{S}}_y{\mathrm{Se}}_{1-y}$ quantum-well structures in a strong electric field is investigated as it depends on the quantum-well width. A quantum-mechanical model is developed which fully takes account of the Coulomb interaction leading to intersubband coupling and strong excitonic effects. Numerical results are presented and compared with measurements. The study focuses on the transition regime between the quantum-confined Stark effect, which is found for well widths smaller than the exciton Bohr diameter, and the Franz-Keldysh effect, which corresponds to the limit of wide wells. Our theory allows for a unified treatment of a wide range of quantum-well widths and applied fields, and provides detailed insight into the origin of the structure of the absorption spectrum through a spatially resolved microscopic absorption coefficient.