Magneto-Optical Absorption Studies of Modulation-Doped CdTe and dMnTe Quantum Wells

We present interband magneto-absorption spectra up to 20 T taken at 2 K for 100 Å CdTe and CdMnTe single and multiple quantum wells containing a two-dimensional electron gas with concentrations ne up to 4 × 1011 cm—2. Without magnetic field B the absorption spectrum is characterized by two strong peaks, whose energy difference increases linearly with the electron concentration ne. This is interpreted in the framework of the many-body theory proposed by Hawrylak. In a magnetic field B, the spectra of high ne (4 × 1011 cm—2) quantum wells show circularly polarized absorption lines. We find that: (i) asBis increased there is a dominant, strongly enhanced absorption transition whose position is related to the zigzags of the Fermi level on the conduction band Landau levels; (ii) at integer values of the filling factorν, in absorption spectra, there is a sudden redshift of this line equal to the cyclotron energy of the electron ħωeh ; (iii) between the discontinuities, in emission spectra, the values of the transition slope are nħωeh (i.e. not the expected values (n + 1/2) ħωeh) where n is the Landau level index and ħωeh represents the sum of the cyclotron energy of the electron and the hole.