MAGNETOOPTICAL STUDY OF CDTE/CD1-XMNXTE MULTIPLE QUANTUM-WELLS WITH LOW POTENTIAL BARRIERS

We present an optical study of multiple quantum wells of CdTe/Cd1-xMnxTe grown with a low manganese concentration in the barrier layers, typically x almost-equal-to 0.05. Owing to this small x the association of the manganese ions in antiferromagnetic pairs is minimized and hence the relative variations of the barrier heights, induced by a magnetic field, are maximized. The structures grow pseudomorphically to the substrate so that the strains in the CdTe and CdMnTe layers are precisely known. In an attempt to determine the valence band offset the energy difference between the light- and heavy-hole excitons has been carefully analysed. We have found that a valence band offset in the range 0.25 to 0.4 of the total band offset is consistent with the experimental data. We find that in these quantum wells with small barrier heights, and hence with small confinement energies, the exciton binding energies may account for a substantial fraction of the splitting. Thus a precise determination of the valence band offset would need a very accurate calculation of these binding energies. The transition from a type I to a type 11 band structure with an applied magnetic field has been investigated. Various simulations show that the large decrease of energy expected for the heavy-hole excitonic gap at this transition can be almost completely compensated by a simultaneous decrease of the exciton binding energy, which explains why no significant features at the transition were observed in our samples.