Unusual magneto-infrared modes in CdMnTe/CdMgTe quantum well structures

We have carried out a magneto-infrared (IR) study on a series of modulation-doped CdMnTe/CdMgTe quantum well samples with a range of carrier concentrations and Mn compositions. Several IR modes have been observed. In the absence of the magnetic field, they are positioned at 123, 157 and 172cm(-1), denoted as B1, M1 and M2, respectively. These are photo persistent modes, which can be activated by white light. Their magnetic field dependence is rather unusual. BI seems to resemble the behavior of the spin-dependent phonon modes, while M2 splits into two branches, M2a and M2b, in magnetic field. The two branches can be resolved clearly at field greater than 10T. Most interestingly, M2b gains intensity at the expense of M2a, when the sampleis tilted in the field, but their transition energies do not change with the tilting angle. The origins of these modes are not yet clear, but it seems that they are resulted from the electron-phonon interactions. (C) 2007 Elsevier B.V. All rights reserved.