Non-resonant Raman spectroscopy studies of a set of CdS films annealed at different temperatures were performed and showed a direct correlation between the width of the Raman peak produced by CdS-like optical phonons and the crystalline quality of the semiconductor phase probed by x-ray diffraction (XRD) and transmission electron microscopy (TEM). In order to decribe the Raman lineshape a model proposed by Trallero-Giner et al (1998 Phys. Rev. B 57 4664) was used, which considers optical phonons confined in small semiconductor spheres with a size distribution. The model is shown to give a good reproduction of the spectra of samples where the semiconductor phase is most crystalline. However, it required too large values of phonon damping to fit the spectra of several other samples, which, according to XRD and TEM data, do contain CdS nano-crystallites. This large broadening of the Raman peak was considered as inhomogeneous, i.e. associated with disorder. Numerical lattice dynamics calculations were performed for 2D binary clusters of arbitrary shape and three kinds of disorder were considered, (i) random variation of the Cd-S bond frequency from one nano-crystallite to another, (ii) cluster shape irregularities and (iii) fluctuations of the nearest-neighbour interaction constant within one cluster. It is shown that 'ensemble disorder' (i) can be responsible for a shoulder above the bulk CdS phonon frequency observed for some of our samples. The effect of shape disorder (ii) is similar to that of the size dispersion producing some inhomogeneous broadening of the peak. In addition, it gives rise to an extra low-frequency mode originating from the top of the acoustic band. The force constant's disorder (iii) is shown to result in a stronger asymmetric broadening of the Raman peak.

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The (In,Fe)Sb layers with the Fe content up to 13 at. % have been grown on (001) GaAs substrates using the pulsed laser deposition. The TEM investigations show that the (In,Fe)Sb layers are epitaxial and free of the inclusions of a second phase. The observation of the hysteretic magnetoresistance curves at temperatures up to 300 K reveals that the Curie point is above room temperature. The resonant character of magnetic circular dichroism confirms the intrinsic ferromagnetism in the (In,Fe)Sb layers. We suggest that the ferromagnetism of the (In,Fe)Sb matrix is not carrier-mediated and apparently is determined by the mechanism of superexchange interaction between Fe atoms (This work was presented at the XXI Symposium Nanophysics and Nanoelectronics, Nizhny Novgorod, March, 13-16, 2017 (book of proceedings v.1, p. 195), http://nanosymp.ru/UserFiles/Symp/2017_v1.pdf)

The layers of a high-temperature novel GaAs:Fe diluted magnetic semiconductor (DMS) with an average Fe content up to 20 at. % were grown on (001) i-GaAs substrates using a pulsed laser deposition in a vacuum. The transmission electron microscopy (TEM) and energy-dispersive x-ray spectroscopy investigations revealed that the conductive layers obtained at 180 and 200 ºC are epitaxial, do not contain any second-phase inclusions, but contain the Fe-enriched columnar regions of overlapped microtwins. The TEM investigations of the non-conductive layer obtained at 250 ºC revealed the embedded coherent Fe-rich clusters of GaAs:Fe DMS. The x-ray photoelectron spectroscopy investigations showed that Fe atoms form chemical bonds with Ga and As atoms with almost equal probability and thus the comparable number of Fe atoms substitute on Ga and As sites. The n-type conductivity of the obtained conductive GaAs:Fe layers is apparently associated with electron transport in a Fe acceptor impurity band within the GaAs band gap. A hysteretic negative magnetoresistance (MR) was observed in the conductive layers up to room temperature (RT). MR measurements point to the out-of-plane magnetic anisotropy of the conductive GaAs:Fe layers related to the presence of the columnar regions. The studies of the magnetic circular dichroism confirm that the layers obtained at 180, 200 and 250 ºC are intrinsic ferromagnetic semiconductors and the Curie point can reach up to at least RT in case of the conductive layer obtained at 200 ºC. It was suggested that in heavily Fe-doped GaAs layers the ferromagnetism is related to the Zener double exchange between Fe atoms with different valence states via an intermediate As and Ga atom.