M. Kulik

RBS and ellipsometric studies of near surface GaAs ion implanted layers

Abstract GaAs samples implanted with Ar+, Al+ and Xe+ ions were studied by using the RBS and ellipsometric methods. The values of thickness of the implanted layers were estimated by both methods and they were in good agreement. These results were also compared with the values of parameters of the depth distribution of implanted ions calculated by SATVAL code. Multilayer models were applied for determination of the optical parameters of investigated samples. The refraction and extinction coefficients of implanted layers increased with the implanted dose. An influence of the type of implanted ion species on the refractive index of oxide layers was observed.

PIXE and magnetic investigations of La x RE 1-x F 3 (RE = Ce,Nd) single crystals

The mixed LaxRE1-xF3 single crystals doped with Gd3+ were grown by a modified Bridgmann- Stockbarger method. The PIXE method was used to the determination of a composition x of this material. The value of x for these samples does not differ more than 2.5 percent and 7.5 percent in LaxCe1-xF3 and LaxNd1-xF3 respectively, from the assumed one. In addition, concentrations of the doped rare earth atoms were controlled by XRF method. The abundance of other than Gd3+ rare earth impurities was estimated to be below 0.058 at percent. The magnetic susceptibility of the single crystals was measured in the temperature range 4-300 K, in a magnetic field B equals 0.2 T applied in the crystallographic plane perpendicular to the c-axis using the Faraday method. The magnetic susceptibility measurements confirm the lack of Ce3+ and Nd3+ clusters in the diluted crystals. The effective spins of hosts Ce3+ and Nd3+ are equal to ½ in the temperature range 4-300 K.

Effect of optical phonon confinement on Raman spectra of porous silicon

Raman scattering line shapes have been calculated for 2D and 3D phonon confinements in porous silicon. The anisotropy of the optical phonon propagation was taken into account for Si, by using realistic phonon dispersion curves obtained by neutron scattering. The theoretical Raman spectra have been compared to the experimental results, and the prevailing nanocrystalline shapes and characteristic dimensions of wire- or sphere-like Si nanocrystallites in porous silicon were estimated.

Dielectric functions, chemical and atomic compositions of the near surface layers of implanted GaAs by In+ ions

The surfaces of (100) GaAs were irradiated with In+ ions. The implanted samples were isobaric annealed at 800°C and then of dielectric function, the surface atomic concentrations of atoms and also the chemical composition of the near surface layers in these implanted semiconductor samples were obtained. The following investigation methods were used: spectroscopic ellipsometry (SE), Rutherford backscattering spectrometry analyses (RBSA) and X-ray photoelectron spectroscopy (XPS) in the study of the above mentioned quantities, respectively. The change of the shape spectra of the dielectric functions at about 3.0eV phonon energy, diffusion of In+ ions as well as chemical composition changes were observed after ion implantation and the thermal treatment. Due to displacement of Ga ions from GaAs by the In+ ions the new chemical compound InAs was formed. The relative amounts Ga2O3 and As2O3 ratio increase in the native oxide layers with the fluences increase after the thermal treatment of the samples. Additionally, it was noticed that the quantities of InO2 increase with the increasing values of the irradiated ions before thermal treatment.

Raman scattering evidence of medium-range order in low fluence Se+-implanted GaAs

The eAect of growing disorder in the 200 keV Se a -implanted GaAs layers has been investigated by Raman scattering for low ion fluences ranging from 1 10 12 to 1 10 14 cm ˇ2 . We observe a softening and asymmetric broadening of the symmetry-allowed LO phonon line, and the same eAect for the TO peak corresponding to the misoriented, recrystallized parts of the implanted material. The average diameters of GaAs nanocrystals were determined using a phonon-confinement model. The presence of the background signal attributed to a boson peak in the Raman spectra indicates that the medium-range order amorphous phase becomes important above the Se a ion threshold fluence of 8 10 12 cm ˇ2 . ” 2000 Elsevier Science B.V. All rights reserved.

Detection of oxygen in porous silicon by nuclear reaction 16O(alpha,alpha)16O

Elastic Recoil Detection and Rutherford Backscattering methods were used to obtain the depth profiles of hydrogen, oxygen and silicon atoms in porous Si layers on Si substrates. Large values of the oxygen concentration suggest a high oxidation degree of the specific surface of porous Si. It supports our earlier hypothesis, based on experimental evidence, that a formation of silicon oxidation oxides in porous layers is essential to the blue emission of light from this material.