Magneto-optical absorption studies of modulation-doped CdTe and CdMnTe quantum wells

We present interband magneto-absorption spectra up to 20 T taken at 2 K for 100 Angstrom CdTe and CdMnTe single and multiple quantum wells containing a two-dimensional electron gas with concentrations n(e) up to 4 x 10(11) cm(-2). Without magnetic field B the absorption spectrum is characterized by two strong peaks, whose energy difference increases linearly with the electron concentration n(e). This is interpreted in the framework of the many-body theory proposed by Hawrylak. In a magnetic field B, the spectra of high n(e) (4 x 10(11) cm(-2)) quantum wells show circularly polarized absorption lines. We find that: (i) as B is 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 factor v, in absorption spectra, there is a sudden redshift of this line equal to the cyclotron energy of the electron no,; (iii) between the discontinuities, in emission spectra, the values of the transition slope are n (h) over bar omega(eh) (i.e. not the expected values (n + 1/2) (h) over bar omega(eh)) where n is the Landau level index and (h) over bar omega(eh) represents the sum of the cyclotron energy of the electron and the hole.