n-AlGaAs/GaAs/n-AlGaAs double quantum wells with an AlAs barrier: Relating the cladding doping level to structural and transport properties

Double quantum wells in the form of an AlGaAs/GaAs/AlGaAs heterostructure with an AlAs barrier a few monolayers thick are fabricated by MBE. Their structural and compositional characterization is carried out by double-crystal XRD and SIMS. Electron mobility is evaluated by Hall-effect measurements for different quantum-well thicknesses. Conditions are identified under which electron mobility can be enhanced by introduction of an ultrathin barrier into a single quantum well. The findings are analyzed from the viewpoint of interface structural quality.Translated from Mikroelektronika, Vol. 34, No. 2, 2005, pp. 98–109.Original Russian Text Copyright © 2005 by Vasilevskii, Galiev, Ganin, Imamov, Klimov, Lomov, Mokerov, Saraikin, Chuev.     

Mossbauer-Spectroscopy Characterization of Nanostructured Magnetic Materials

Two mechanisms are examined underlying the formation of the magnetic hyperfine structure in the Mossbauer spectra of magnetic materials containing nanoparticles. The absorption spectra of ⁵⁷Fe nuclei in Fe-Cu-Nb-B nanostructured magnetic alloys are evaluated within the generalized two-level relaxation model, which includes interparticle interaction. All the unconventional features of the spectra are thus explained in qualitative terms. Furthermore, the precession of the magnetic moments of nanoparticles in a magnetic anisotropy field is investigated. It is shown that in a precessing hyperfine field the nuclear g factors should be subject to renormalization. As a result, the hyperfine spectra should undergo a radical transformation. It is concluded that the conventional techniques of Mossbauer-spectra evaluation in the context of nanostructured magnetic materials should be modified to include the transformation.     

Characterization of a Quantum Well in an Si/Si1–xGex/Si Heterostructure by X-ray Diffractometry

Rocking curves with a pronounced pendulum-solution pattern are obtained for Si_{1 – x} Ge _x /Si specimens with a single quantum well (QW) by double-crystal x-ray diffractometry. These oscillations are typical of the rocking curves for GaAs multilayers with QWs. With Si–Ge multilayers, they are obtained for the first time. The Ge depth profiles of the QW are reconstructed from the rocking curves. As a result, the thicknesses of both QW interfacial layers are estimated.     

Diluted magnetic semiconductors: Actual structure and magnetic and transport properties

An experimental investigation is conducted into electrical-transport, magnetic, optical, and structural properties of GaAs-based diluted-magnetic-semiconductor heterostructures containing a Ga_1?x In _x As quantum well and a Mn delta layer 0.5–1.8 ML thick, separated by a GaAs spacer of thickness 3 nm. Ferromagnetic features are observed in the electrical transport and the Hall effect, which involve the flow of holes across the quantum well. They indicate carrier spin polarization in the quantum well. The combined use of high-resolution x-ray diffraction and x-ray reflectivity has made it possible to reliably identify structural-parameter profiles for both the quantum well and the Mn delta layer. It is thus established that the distribution of Mn atoms is nonuniform, both horizontally and vertically. This finding suggests a conception whereby the Mn delta layer divides into nanoscale ferromagnetic-ordering regions and paramagnetic regions. Magnetic and electrical-transport properties of the heterostructures are discussed within this framework.