Electroabsorption studies on quasi-three-dimensional and quasi-two-dimensional excitons in (Zn,Cd)Se/Zn(S,Se) structures

The electro-optical properties of (Zn,Cd)Se/Zn(S,Se) quantum well structure s grown on GaAs substrates have been studied with differential electroabsor ption spectroscopy at room temperature and compared to model calculations. (Zn,Cd)Se wells of 20, 10, and 4x5 nm are investigated, corresponding to we ll widths of four, two, and one times the exciton Bohr radius in this mater ial system, respectively. We observe the quantum confined Stark effect for the 4x5 nm sample and find a Stark shift of 18 meV in the heavy-hole excito n peak for an electric field change from 82 to 175 kV/cm. In contrast, the 10 nm sample shows a rather weak and more Franz-Keldysh-like signal. We sho w that the 20-nm-thick quantum-well sample behaves like bulk material, i.e. , the electro-absorption signal is well described by Franz-Keldysh oscillat ions. (C) 1999 American Institute of Physics. [S0021-8979(99)03620-8].