L.L. Golik

Resonant enhancement of the transversal Kerr effect in the InMnAs layers

Spectral dependences of the transversal Kerr effect (TKE) as well as of the real and imaginary parts of the permittivity of InMnAs layers were studied. Pulsed laser ablation of Mn and InAs targets was used to form the layers on GaAs(100) substrates. Spectra of the optical constants and TKE depended substantially on layer fabrication conditions and testified to the presence of MnAs inclusions in the samples. The cross-sectional transmission electron microscopy revealed the presence of inclusions of size 10-40 nm in the layers. At room temperature a strong resonant band was observed in the TKE spectra of the InMnAs layers in the energy range of 0.5-2.2 eV. In this band the TKE was comparable in magnitude but opposite in sign to that in the strong ferromagnetic MnAs. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the InMnAs semiconductor host. Modelling the TKE spectra for (InAs)(1 - X):(MnAs)(X) nanocomposites in the effective-medium approximation (Maxwell-Garnett approximation) confirmed the assumption on the plasmon mechanism of the resonant enhancement of the transversal Kerr effect in the InMnAs layers.

Mechanism for strong nonlinearities in the Faraday rotation and absorption in the ferromagnetic semiconductor CdCr2Se4

At high laser radiation intensities a strong nonlinear Faraday rotation (FR) may be observed in a relatively narrow energy band near the absorption edge of CdCr2Se4. To study the nature of this effect, we investigated the influence of the incident radiation intensity on the spectral properties of the FR and the circularly polarized light absorption, and studied the dynamics of the observed nonlinearities. As the laser radiation intensity increases, we find a strong growth of the resonance structure at the absorption edge and an enhancement of the FR in the band associated with the resonance. The nonlinear FR is a non-monotonic function of the radiation intensity and reaches a local maximum, which is about twice the value of the rotation angle for the linear effect. The dynamics of the observed nonlinearities show that the nonlinearities are caused by photo-excited charge carriers. These carriers screen the internal electrical fields and lead to a narrowing and growth of the excitonic resonance in the abso...

Nonlinear Faraday effect near the fundamental absorption edge in the ferromagnetic semiconductor CdCr2 Se4

A sharp increase of the Faraday rotation with increasing incident radiation power is observed in a band near the fundamental absorption edge of the ferromagnetic semiconductor CdCr2 Se4. The magnitude of the effect is a nonmonotonic function of the radiation intensity. The effect is explained by narrowing of an excitonic resonance as a result of screening of the internal electric fields by photoexcited carriers.

On Nature of Resonant Transversal Kerr Effect in InMnAs and GaMnAs Layers

Optical and magneto-optical properties of In(Ga)MnAs layers fabricated by laser ablation on GaAs(100) substrates were studied. Spectra of the optical constants and the transversal Kerr effect (TKE) depended substantially on the conditions of layer fabrication and testified to the presence of MnAs inclusions in all the samples. The cross-sectional transmission electron microscopy revealed the presence in the layers of inclusions 10-40 nm in size. At room temperature, a strong resonant band was observed in the TKE spectra of some In(Ga)MnAs layers in the energy range 0.5-2.7 eV. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the semiconductor host.

Transversal Kerr Effect of In1-xMnxAs layers prepared by ion implantation followed by pulsed laser annealing.

In1− x Mn x As (x = 6.9%) layers prepared by ion implantation and subsequent pulsed laser annealing have been studied using the magnetooptical transversal Kerr effect (TKE) and spectral ellipsometry. Ellipsometry data reveal the good crystal quality of the layers. The samples show ferromagnetic behaviour below 77 K. Near the absorption edge of the parent InAs semiconductor, large TKE values are observed. In the energy regions of the transitions in the Γ and L critical points of the InAs Brillouin zone, there are several clearly defined structures in the low-temperature TKE spectra. We have calculated the spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) for our samples. A number of extrema in the obtained MCD and PT spectra are close to the energies of transitions in the critical points of the parent semiconductor band structure, which confirms the intrinsic ferromagnetism of the Mn-doped InAs layers.

Magneto-Optical Evidence for Intrinsic Ferromagnetism in (Ga,Mn)As Layers Grown by Pulsed Laser Deposition

GaMnAs layers fabricated on GaAs(001) substrates by laser ablation technique were studied using the magneto-optical transversal Kerr effect (TKE) (E = 0.5 - 4.0 eV) and spectral ellipsometry (E = 1.4 - 4.5 eV). Obtained spectral, temperature and magnetic field TKE dependences shown that the used technique allowed us to obtain ferromagnetic (Ga,Mn)As layers, whose composition was close to single-phase one (without MnAs inclusions). Spectral dependences of the off-diagonal components (e’ = e’1 - ie’2) of the permittivity tensor and also of the magnetic circular dichroism (MCD) were calculated for ferromagnetic (Ga,Mn)As sample. The calculated dependences were compared with the published magneto-optical spectra of (Ga,Mn)As layers grown by molecular beam epitaxy.

Peculiarities in Optical and Magneto-Optical Spectra of GaMnSb Layers Grown by Laser Ablation

Optical and magneto-optical properties of GaMnSb layers fabricated on GaAs (001) substrates by laser ablation technique were studied using spectral ellipsometry (E =1.24-3.25 eV) and the transversal Kerr effect (TKE) (E = 0.5 4.2 eV) as well as atomic and magnetic force microscopy. Spectra of the constituents of the diagonal components of the permittivity tensor as well as TKE depended substantially on the layer fabrication conditions. At room temperature a strong resonant band was observed in the TKE spectra for the GaMnSb layers with low Mn content in the energy range E 0.5-1.5 eV. This resonant TKE band was explained by excitation of surface plasmons in MnSb nanoclusters, which arose during the growth of the layers. In the energy region E >1.5 eV the TKE spectra were related to interband transitions in MnSb inclusions.

Optical and magneto-optical spectroscopy of thin ferromagnetic InMnAs layers

Spectral dependences of the refractive n(hν) and absorption k(hν) indices (hν= 1.2–4.4 eV) and the magneto-optical constant δ(hν) (hν = 0.5–4.4 eV) of the transverse Kerr effect of the InMnAs layers produced by laser deposition have been studied. The spectra of the diagonal ɛ(hν) and off-diagonal ɛ′hν) components of the permittivity tensor of the layers have been found. A comparison of the spectral dependences δ(hν), ɛ′(hν) and ɛ′2 × (hν)2 of the InMnAs and MnAs layers have been performed. Features in the spectra of the InMnAs layers have been attributed to a competition between the contributions of the In1 − x MnxAs matrix and MnAs inclusions.

Quantum well related conductivity and deep traps in SiGe/Si structures

Electrical transport and traps in vertical SiGe/Si QW structures of low background doping level are studied in the presented report. Temperature activation of holes from the quantum well was found to determine the vertical current through Si/SiGe/Si structures at T > 160 K. At lower temperatures (T < 130 K), the current mechanism is attributed to a thermally activated tunneling of holes from quantum well. Deep traps are observed in the Si/SiGe/Si structures in high concentration (1011 – 1012 cm-2). Traps are most likely assistance in the current in the vertical Si/SiGe/Si structures as recombination centers near the QW.

Phase Separation in GaMnAs Layers Grown by Laser Pulsed Deposition

GaMnAs layers grown by pulsed laser deposition were studied by magneto-optical transversal Kerr effect spectroscopy, spectral ellipsometry, resistivity and the Hall effect measurements, and magnetometry. The growth regimes for magnetically inhomogeneous layers containing Mn-enriched ferromagnetic regions with different composition and sizes were established. The layers grown at a temperature of 300°C exhibit a ferromagnetic behavior at temperatures below 80 K, which is conditioned by the presence of local ferromagnetic (Ga,Mn)As regions in the paramagnetic matrix. The nature of peculiarities in the TKE spectrum of these layers is discussed.