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Articles you may be interested inEffect of Sb incorporation on structure and magnetic properties of quaternary ferromagnetic semiconductor (Ga, Mn)(As, Sb) thin films Ferromagnetic (Ga,Mn)As nanowires grown by Mn-assisted molecular beam epitaxy Epitaxial growth and properties of III-V magnetic semiconductor (GaMn)As and its heterostructures GaMnAs layers with Mn contents from 0.05% to 7% were grown by low temperature molecular beam epitaxy. At substrate temperatures lower than 300°C and in this composition range a uniform ternary GaMnAs compound can be grown without MnAs precipitation. Reflection high energy electron diffraction intensity oscillations recorded during GaMnAs growth were used to calibrate the composition of the GaMnAs films with high accuracy ͑better than 0.1%͒. Films containing more than 1% Mn exhibit a ferromagnetic phase transition with Curie temperatures from a few up to 70 K depending on the composition and other growth parameters. In contrast to previous reports we have observed this transition also in the case of layers grown at very low substrate temperatures ͑below 200°C͒.

Photoluminescence (PL) of porous silicon (pSi) prepared from Czochralski silicon (Cz-Si) annealed up to 1620 K at enhanced pressure of argon up to 1 GPa (HP-HT treatment) was investigated. The intensity of PL with maximum at 680±720 nm decreases with the pressure for pSi prepared from the substrates treated at 1400 K, and increases with the pressure for pSi prepared from the substrates treated at 1620 K. The pSi films prepared from the HP-HT treated substrates were relaxed, contrary to those on the substrates annealed at 1620 K for 30 min at 10 5 Pa. Although our results revealed that photoluminescence properties of pSi depend significantly on the presence of defects created during the oxygen precipitation process, the role of other defects such as non-radiative recombination centres and metallic contamination should be still under consideration.

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Two-dimensional maps of x-ray diffuse scattering (DS) in a reciprocal space for a real crystal containing Coulomb deformation centres (clusters or dislocation loops) were calculated using a new dynamical theory developed for a crystalline media with homogeneously distributed defects. Such maps were calculated for both the fundamental, 400, as well as the quasi-forbidden, 200, reflections of x-rays (CuKα 1 radiation) for a binary crystal (GaAs). They were also discovered experimentally in the GaAs films heavily doped with Si (up to 10 20 cm −3) by means of a Philips three-crystal diffractometer. The procedure for fitting calculated values of differential DS to the experimental data enabled not only the integral characteristics of the structure's perfection (Debye-Waller static factor, L H , and coefficient of extinction of radiation due to additional energy losses on defects, µ d) but also the average radius,r, and concentration,n, of microdefects (precipitates to be obtained).

Lattice constants of GaAs layers grown by molecular beam epitaxy were examined by using the high resolution x-ray diffractometer. For highly doped samples ͑up to 9ϫ10 18 cm Ϫ3 of free-electron concentration͒ we observed an increase of the lattice constant with respect to the undoped layers. Since substitutional silicon atoms decrease the lattice constant of GaAs, the results are explained by the influence of free-electrons via the deformation potential of the ⌫ minimum of the conduction band. The best fit to our diffractometric data was obtained for the band-gap deformation potential equal to Ϫ8.5 eV.

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The paper shows an influence of doping on lattice constant of a semiconductor. Three effects are discussed: (i) "size" echect caused by a different ionic radii of dopant and host atoms, (ii) lattice expansion by free electrons proportionally to the deformation potential of the conduction-band minimum occupied by this charge, (iii) different thermal expansion of the undoped and doped samples. The experiments have been performed by using the high resolution X-ray dichractioii at 77-770 K oii AlGaAs:Te and GaAs:Si.