A. V. Komarov

MAGNETIC-FIELD AFFECTED LUMINESCENCE OF MN2+ IONS IN ZN1-XMNXSE COMPOUNDS UNDER RESONANCE EXCITATION OF EXCITONS

Abstract Under the resonance excitation of free excitons in cubic Zn 0.99 Mn 0.01 Se crystals we observed an unexpectedly strong effect of applied magnetic field on the intra-centre luminescence of the Mn 2+ ions. Strong enough difference is revealed between the manifestation of this effect in σ + and σ - Mn 2+ luminescence under σ + and σ - exciton pumping. The observed effect is attributed to a specific influence, left out of the consideration in earlier studies, of the carrier-ion exchange interaction on the energy transfer from excitons to the subsystem of the Mn 2+ ions.

Interface structural defects and photoluminescence properties of epitaxial GaN and AlGaN/GaN layers grown on sapphire

Overall characterization of the GaN and AlGaN/GaN epitaxial layers by X-ray diffractometry and optical spectral analysis is carried out. The layers are grown by metalloorganic gas-phase epitaxy on (0001)-oriented single crystal sapphire wafers. The components of strains and the density of dislocations are determined. The effects of strains and dislocations on the photoluminescence intensity and spectra are studied. The results allow better understanding of the nature and mechanisms of the formation of defects in the epitaxial AlGaN/GaN heterostructures.

Optical polarization anisotropy of quantum wells induced by a cubic anisotropy of the host material

The optical polarization anisotropy of quantum wells (QW) in structures fabricated from materials with cubic symmetry due to the anisotropic character of the Luttinger Hamiltonian for the valence band is studied. The matrix elements of interband optical transitions are shown to be different for different orientations of the linear polarization of light, oriented in the plane of a structure, provided that the structure growth axis does not coincide with any of the main crystallographic directions, i.e., with either [100],[010],[001] or [111]. The degree of this in-plane anisotropy of the polarization is calculated theoretically within an appropriate model for arbitrary structure growth orientation. The polarization anisotropy is experimentally detected for the fundamental 1hh–1e transition by studying the reflectivity from [120]-oriented Cd0.8Mn0.2Te/CdTe/Cd0.8Mn0.2Te QWs. At the same time the effect is shown to be absent in the case of QW grown along [100] direction. The measured polarization anisotropy in the former case shows a predicted π-periodicity as the polarization direction is rotated within the plane of the QW. The magnitude of the effect is also in qualitative agreement with the model. Quantitatively, the measured values tend to be some what larger than those predicted by the model. Surprisingly, the polarization anisotropy of the reflection by the barrier excitons is also detected. For the [120]-oriented structures this anisotropy has, approximately, the same magnitude as the one of the exciton transitions in the QWs. In the structure grown along [100], the anisotropy of the reflectivity of the barrier exciton transitions is also observed, although it is much smaller in magnitude. Some hypothetical explanations of these observations are put forward.

Nature of low-energy optical emission in doped AlGaN∕GaN heterostructures

Photoluminescence (PL) in modulation-doped and nominally undoped AlxGa1−xN∕GaN heterostructures was studied and compared with PL spectra of GaN films grown on sapphire substrates. It is demonstrated that optical emission in the energy range of 3.3–3.46eV related to the two-dimensional electron gas radiative processes can be completely suppressed in modulation-doped AlxGa1−xN∕GaN heterostructures. Instead of this, an intense broad long-wavelength emission attributed to the recombination of donor-acceptor pairs in the lower energy range of 2.7–3.3eV is revealed. This spectral transformation is explained by the presence of deep-level defect-related acceptor centers in AlxGa1−xN∕GaN heterostructures introduced at the modulation doping of the AlxGa1−xN barrier layer.

Investigation of the structure of the edge of the valence band of Cd1−xMnxS crystals on the basis of magnetooptical measurements

The results of magnetooptical studies are reported for Cd1−xMnxS crystals with concentrations of the magnetic component x1=0.0056, and x2=0.0013, x1=0.0002 at T=2 K in a magnetic field H⩽3.5 T for H⊥c and H∥c, where c is the hexagonal axis of the crystal. The first reliable confirmation of spin splitting of the exciton reflection spectra of the B exciton transition is successfully obtained as a result of working in an H⊥c experimental geometry. The values of the crystal-field and spin-orbit interaction parameters Δ1, Δ2, Δ3 and the exchange constants Je and Jh of Cd1−xMnxS crystals for achieving the best description of the experimental results in the mean exchange field approximation are found on the basis of the data obtained for H⊥c and for H∥c. An analysis shows that the main qualitative features of the observed reflection spectra for the entire series of investigated Cd1−xMnxS crystals can be described only if the condition (Δ1−Δ2)<0 is satisfied.