Radiative recombination in CdTe/MnTe quantum wells: Emission from near infrared to blue wavelengths

A series of strained single-quantum-well (SQW) CdTe/MnTe structures with well thicknesses ranging from approximately 50 to 10 angstrom were studied. Raman experiments indicate that the lattice mismatch of approximately 3.2% is coherently accommodated if the MnTe barrier layers remain sufficiently thin (typically approximately 40 angstrom). As an example of the effects of the strong quantum confinement in these heterostructures, photoluminescence spectra (normalized amplitudes) obtained from three CdTe quantum-well samples with well thickness of approximately 22, 15, and 10 angstrom, respectively, are shown. The emissions occur in the red, yellow, and blue for the n = 1 exciton recombination in the structures. The blue emission (at approximately 478 nm) shows how confinement effects are responsible for increasing the optical gap of CdTe by approximately 1 eV. Steady-state and transient spectroscopy were applied to the quantum wells to detail the confined electronic states. An approximate conduction-to-valence band offset ratio of approximately 10:1 and excitonic binding energies in the range of 20-25 meV were inferred. Temperature-dependent linewidth studies gave a measure of the exciton-optical phonon coupling strengths that was a factor of approximately 5-8 larger than values reported for the GaAs quantum wells.