O. Goede

Optical study of octahedrally and tetrahedrally coordinated MnSe

Abstract Octahedrally and tetrahedrally coordinated MnSe MBE-layers and polycrystalline thin films and octahedrally coordinated (Mn, Cd)Se (xMn ⩾ 0.8) bulk crystals are investigated by luminescence and excitation spectroscopy. The results are discussed in the framework of a ligand-field-model. Below the Neel temperature (TN) a significant shift of the Mn2+ d-d excitation bands to higher energies is found for the polycrystalline and bulk samples, which is caused by a spin-ordering- induced energy relaxation of the various Mn2+ states. No indication for an antiferromagnetic phase transition is found in the case of the quasi-2D-MBE-layers of MnSe.

Magneto-optical study of asymmetric CdTe/(Cd,Mn)Te double-quantum-well nanostructures

Abstract A strained CdTe/(Cd,Mn)Te double-quantum-well nanostructure, grown by MBE on InSb substrate, is studied by CW and ps luminescence, reflection, and excitation spectroscopy in magnetic fields up to 5 T. The two CdTe quantum-wells of the sample have different well widths and are separated by a thin (Cd,Mn)Te barrier. A fast exciton transfer is observed from the higher-energy lh and hh states of the narrow well into the hh state of the broad well. The exciton energies in the wells and barriers and their magnetic-field induced splitting can consistently be explained by model calculations, taking into account the strain known from X-ray diffraction measurements. The decay times of the various luminescence bands are determined.

Optical study of the antiferromagnetic phase transition in (Cd,Mn)S at highest Mn concentration

Abstract Luminescence emission and excitation measurements are used to study the antiferromagnetic phase transition in (Cd,Mn)S single crystals and thin films in the case of highest Mn concentrations 0.8 ≤ xMn ≤ 1. The spin-freezing temperature TN(xMn) is determined from the temperature dependence of the Mn2+ EPR linewidth. The samples having rocksalt or zincblende/wurtzite structure show luminescence band near 1.5 and 1.8 eV, respectively. Below TN(xMn) a significant shift of the corresponding Mn2+ d-d excitation bands to higher energies is found, which is ascribed to the different spin-ordering induced energy relaxation in ground and excited states of the Mn2+ ions. The superexchange interaction parameters for the various excited Mn2+ states are obtained in a mean-field approximation. The measured luminescence decay parameters indicate the energy transfer between the Mn2+ ions to be also influenced by the antiferromagnetic spin ordering.

Exciton transfer in CdTe(Cd,Mn)Te-double quantum well structures

Abstract A series of asymmetric CdTe ( Cd,Mn ) Te double quantum well structures, grown by MBE on InSb substrates, are studied by luminescence, excitation, and reflection spectroscopy in magnetic fields up to 9T. The well widths are 4 and 8 nm; respectively, the width of the inner barrier varies in the range 2.5 to 15 nm. The exciton transfer from the narrow into the wide well is found to be strongly dependent on the width of the inner barrier. The decay of the various luminescence bands after 5 ps-pulse excitation at various excitation energies and the dependence of the exciton transfer on a magnetic field are investigated. The results can be explained on the basis of an effective-lifetime model assuming an independent tunneling of electrons and holes.

Optical properties of mercurycadmium telluride based superlattices

Abstract Optical spectra of the dielectric function as well as absorption and reflection spectra are calculated for HgTe/CdTe superlattices over a wide range of photon energies including E 0 , E 1 and E 2 derived transitions. Electronic structure data are obtained by means of tight binding theory. Theoretical results are compared with experimental data measured on a 70 A-70 A HgTe/CdTe superlattice.

Luminescence study of CdTe/(Cd,Mn)Te-MQW structures in magnetic fields

Abstract Strained CdTe/(Cd,Mn)Te-MQW structures, grown by MBE on InSb substrates, are investigated by luminescence and reflection spectroscopy. Free and donor-bound (D 0 X) exciton and donor-acceptor-pair (DAP) transitions are studied in dependence on magnetic field strength and orientation. The D 0 X binding energy is found to decrease with increasing magnetic field. magnetic polaron effects are observed both for D 0 X and DAP transitions. In the case of D 0 X spin-pinning with respect to the normal axis of the quantum well is seen. A discussion of the results on the basis of a Kronig-Penney model calculation taking into account the strain effects yields a large valence band offset, and a valence/conduction band offset ratio of 1.6 to 1.8 is determined.

Magneto-optical study of ZnSe/(Zn,Mn)Se and ZnSe/(Zn,Cd,Mn)Se quantum well structures and superlattices

Abstract Quantum well structures with semimagnetic barriers, ZnSe /( Zn , Mn ) Se , or semimagnetic wells, ( Zn , Cd , Mn ) Se / ZnSe , are studied by luminescence and reflection spectroscopy in an external magnetic field up to 7.5 T.A. unique offset dependence on the manganese concentration and a type conversion of the ZnSe /( Zn , Mn ) Se heterostructures due to the giant Zeeman splitting of the barriers are found. In the ( Zn , Cd , Mn ) Se / ZnSe structures, a strong reduced energy transfer from the exciton states to the Mn internal transition was found, which is further suppressed by an increasing magnetic field. Therefore (Zn,Cd,Mn)Se quantum wells can be proposed to be suitable and effective for tuneable blue-green laser devices in an external magnetic field. The field dependent energy splitting both of well and barrier excitons are significantly anisotropic with respect to the orientation of the magnetic field B parallel or perpendicular to the growth axis. This magneto-optical anisotropy can be explained by the mixing of the heavy and light hole states in the framework of a multi-band envelope-function approximation.

MBE growth and characterization of (Zn, Mn)Se/ZnSe and MnSe/ZnSe structures on (001) GaAs

Abstract The MBE growth of ZnSe, (Zn,Mn)Se, MnSe, and related quantum well structures has been studied. Results are presented concerning the effect of growth interruptions and optical properties of SQW and MQW structures.

Magneto-optical study of Mn containing broad gap II–VI quantum well structures and superlattices

Abstract Semimagnetic ZnSe/(Zn,Mn)Se single and multiple quantum well structures are studied by luminescence and reflection spectroscopy in a magnetic field up to 7.5 T. Using the strain-induced heavy and light hole splitting of the barrier and well excitons the valence band offset is determined in the framework of a Kronig-Penney model calculation. A unique offset dependence on the manganese concentration and a type conversion due to the giant Zeeman splitting are found.

Magneto-optical anisotropy of CdTe/(Cd, Mn)Te quantum-well structures due to lattice-misfit induced strain

Abstract The magneto-optical anisotropy of semimagnetic CdTe/(Cd, Mn)Te multiple-quantum-well structures and superlattices, grown by MBE on InSb substrates, is studied by luminescence and reflection spectroscopy in magnetic fields up to 5 T. It is shown that the lattice-misfit induced biaxial strain in these structures leads to significantly different shifts and splittings of the exciton energies in the semimagnetic (Cd, Mn)Te barriers by a magnetic field applied parallel and perpendicular to the strain axis. The measured anisotropic barrier exciton peak shifts are found to be in quantitative agreement with perturbation theory calculations. The magneto-optical anisotropy of the well excitons, being expected as a consequence, are discussed on the basis of the corresponding experimental results.