Dependence of X— Magnetoabsorption on Electron Concentration in a CdTe Quantum Well

The oscillator strength for the absorption transition that creates the negatively charged exciton (X—) is measured as a function of electron density ne and magnetic field in a CdTe/CdZnMgTe quantum well containing a two-dimensional electron system inserted in a Schottky diode. In fixed high magnetic field (8 T), the X— oscillator strength per unit area first increases linearly with ne, reaches a maximum at Landau level filling factor ν = 1, then decreases approximately linearly with ne to disappear at ν ≈︂ 2. Studies of X and X— in zero magnetic field show that X— is less sensitive than X to screening by the electron gas.