M. Surma

Parabolic quantum wells of diluted magnetic semiconductor Cd1−xMnxTe

We report on the growth by molecular beam epitaxy of II‐VI semiconductor parabolic quantum wells. Cd1−xMnxTe diluted magnetic semiconductor was chosen for constructing these structures because of its extreme sensitivity to the presence of a magnetic field. Photoluminescence excitation spectra revealed several series of energetically equidistant peaks due to interband optical transitions. The energy separation in a given series scales proportionally to the inverse width of the quantum well as expected for a parabolic confining potential. Analysis of the spectra made possible a model‐independent determination of the valence band offset in CdTe/Cd1−xMnxTe.

On the nature of the anti-Stokes luminescence in chromium-doped ZnSe crystals

Abstract An efficient blue anti-Stokes luminescence is observed in ZnSe:Cr. The anti-Stokes emission is related to the two-step ionization transitions of Cr. We also suggest that some co-operative processes can contribute to the excitation of the anti-Stokes emission.

Growth by molecular beam epitaxy and magnetooptical studies of (100)- and (120)-oriented digital magnetic quantum well structures

Abstract We report on growth by molecular beam epitaxy and magnetooptical investigations of digital alloys of diluted magnetic semiconductors. The digital alloys, i.e., very short-period superlattices, of interest here, were grown from nonmagnetic CdTe and magnetic Cd1−xMnxTe. In particular, quantum well structures containing the digital alloys in the regions of the quantum wells were fabricated. We searched for theoretically expected modifications of magnetic properties of digitally grown materials compared to those of random substitutional alloy counterparts. We monitored the magnetic behavior in our samples by studying their magnetooptical properties. We detected clear differences between magnetizations in random and digital alloys in samples grown along the 〈100〉 crystallographic direction. Unexpectedly, no modification of the spin-splitting (and, thus, of the magnetization) were observed in the case of digital quantum wells grown in the 〈120〉 crystallographic direction. On the other hand, exciton magnetic polaron binding energy in the latter structures was consistently greater by 10–20% than this quantity in similar samples grown along the 〈100〉 direction. The increase can be qualitatively understood in terms of the heavy hole mass anisotropy.

Influence of strain and repeated annealing on interface mixing in annealed CdTeCdMnTe quantum wells

Abstract We use the magnetooptical method of interface characterisation to study Mn diffusion caused by annealing of CdTe quantum wells with CdMnTe barriers. To investigate influence of strain in the sample on the diffusion process we anneal structures grown pseudomorphically on thick buffers of different lattice constant. Our results show that the strain in the quantum well strongly enhances diffusion of Mn2+ ions into the quantum well during annealing. Measurements of samples annealed twice show a strong enhancement of the diffusion efficiency during the second process.

Exciton dynamics in MBE grown CdTeCdMnTe multiple quantum wells

Abstract A comprehensive photoluminescence (PL), PL decay and PL excitation study of exciton properties in CdTe CdMnTe quantum wells (QWs) is presented. We report the observation of mobile, quasi-mobile and localized excitons for structures grown on different substrates and two growth directions. The observed PL decay times range (for e.g. 100 A QW) from 100–120 ps, for localized excitons, to 350 ps, for mobile excitons. For narrow QWs, strain fluctuations and magnetic polaron formation strongly affect exciton dynamics.

Interplay between exciton properties and interface quality in CdTe/CdMnTe quantum well structures grown by molecular-beam epitaxy

Abstract The results of systematic study of range of the CdTe/CdMnTe quantum well structures grown on four different substrates, for two growth directions and by two growth methods — conventional molecular-beam epitaxy and atomic layer epitaxy are presented. We show that emission decay measured strongly depends on the extent of exciton localization. For structures grown by atomic layer epitaxy an inter-island exciton migration is observed.

Exciton Transfer in Multiple Quantum Well Structures of CdTe/CdMnTe Grown by Molecular Beam Epitaxy

The direct evidence for the efficient transfer of excitons from 4 nm and 6 nm to 10 nm wide CdTe quantum wells is presented based on the results of photoluminescence and photoluminescence excitation investigation. Efficient transfer is observed for quantum wells separated by thick (50 nm) CdMnTe barriers containing 10% or 30% Mn fraction. A new mechanism of the transfer is proposed, which involves long range dynamic magnetic interactions between free/bound excitons and Mn ions in the CdMnTe barrier regions of the structure.