We report on magnetooptical studies of Cd_(1-x)Mn_xTe and Cd_(1-y)Mg_yTe spatially graded quantum well (QW) structures. The photoluminescence excitation and transmission spectra were measured in a magnetic field for trapezoidal, parabolic and half-parabolic quantum wells grown by MBE using the so called "digital" or pulsed flux technique. the composition gradient along the growth direction was checked by cross sectional transmission electron microscopy. The peaks appearing in the spectra were assigned to interband excitonic transitions between different confined levels of electrons and holes. Apart from diagonal transitions (e.g., those preserving the level quantum number) we also observed nondiagonal transitions, usually not dipole-allowed in standard rectangular QWs. This enabled us to determine with high precision the valence band offsets in CdTe/MnTe and CdTe/MgTe systems. The observation of ls and 2s excitonic transitions demonstrated that the exciton binding energy is particularly large in QWs with a parabolic confining potential.
展开▼
