Mf Wu

Direct evidence of spontaneous quantum dot formation in a thick InGaN epilayer

We report a direct observation of quantum dots formed spontaneously in a thick InGaN epilayer by high resolution transmission electron microscopy. Investigation of a (280 nm thick) In0.22Ga0.78N single layer, emitting in the blue/green spectral region, reveals quantum dots with estimated sizes in the range of 1.5–3 nm. Such sizes are in very good agreement with calculations based on the luminescence spectra of this specimen.

Aligned and twinned orientations in epitaxial CoSi2 layers

Heteroepitaxial CoSi2 layers have been made by ion beam synthesis and solid phase epitaxy in Si〈111〉 substrates. Using the x‐ray rocking curves of the asymmetric (331) reflections we are able to determine very accurately the relative amount of aligned (type A) and twinned (type B) CoSi2 in samples with different thicknesses. It is shown that for epilayers thinner than 360 A, the relative amount of type A CoSi2 decreases from 100% to 30%.

Formation of buried and surface cosi2 layers by ion-implantation

Abstract The formation is studied of buried CoSi 2 layers and surface CoSi 2 layers formed by high-dose ion implantation in an energy range of 30 to 160 keV combined with conventional furnace annealing or with rapid thermal processing. The crystalline quality, the phase of the buried and surface silicide layers, the abruptness of the interfaces and the electrical transport properties are studied by RBS, channeling, cross-sectional TEM, Mossbauer spectroscopy and resistivity measurements. The stability of the buried and surface CoSi 2 layers at temperatures between 1000°C and 1200°C is also studied and compared with the results for MBE-grown samples.

Antiparallel crystal orientation in CoSi2 epitaxial bilayers formed by ion implantation

Orientation and strain in buried CoSi2 layers have been studied in a Si/CoSi2/Si/CoSi2/Si(111) structure. Using a well defined implantation and annealing procedure, a unique combination of CoSi2 epitaxial layers was obtained having the same strain but an opposite orientation. These novel structures are interesting for epitaxial growth studies and may have important device applications.

Strain and orientation in epitaxial CoSi2(111) layers formed by ion implantation

Abstract Strain and orientation in epitaxial CoSi 2 (111) layers formed by ion implantation have been studied by RBS/channeling and X-ray rocking curve measurements. For the thickness range (20–47 nm) of the epilayers studied, the average misalignment ΔΨ ( Ψ = 35.26°) and perpendicular strain ϵ ⊥ x are 0.30° and −1.87% respectively, which shows that the strain in our epilayers is larger than in the thicker layers prepared by ion implantation and in the MBE grown layers with similar thickness range, but it is still far from a completely strained layer. Our results also confirm that a pure type A or predominant type A oriented epitaxial CoSi 2 layer, which is rather difficult to prepare by the conventional UHV procedure, can easily be formed by ion implantation. However, for epilayer thicknesses lower than 36 nm, a correlation between the epilayer thickness and orientation is clearly present.

Orientation and strain of single and double CoSi2 epitaxial layers formed by ion implantation

Abstract Orientation and strain in buried CoSi2 layers have been studied in Si/CoSi2/Si(111) and Si/CoSi2/Si/CoSi2/Si(111) structures. Using a well defined implantation and annealing procedure, a unique combination of CoSi2 epitaxial layers was obtained having the same strain but a variable orientation. These novel structures are interesting for epitaxial growth studies and may have important device applications.

Formation of buried cosi2 layers by ion-implantation, studied by mossbauer-spectroscopy and rutherford backscattering spectroscopy

Abstract Buried silicide layers were formed by high dose implantation of cobalt in silicon in an energy range from 50 to 160 keV. The ion beam consisted of 59Co alternated with a small fraction of 57Co, the radioactive parent of the 57Fe Mossbauer isotope. After implantation, the system was thermally annealed at different temperatures using conventional furnace annealing. After annealing at 600°C, the Mossbauer spectrum of CoSi2 appeared. The crystalline quality of the top silicon layer and the buried silicide layers, as well as the abruptness of the interfaces, were studied by Rutherford backscattering spectroscopy, channeling spectroscopy and transmission electron microscopy.

Formation of buried CoSi2 layers by ion implantation and their stability at high temperatures

Abstract The formation is studied of buried CoSi 2 layers formed by high dose ion implantation in an energy range of 50 to 160 keV combined with conventional furnace annealing in various ambients or with rapid thermal processing. The crystalline quality of the top Si layer and the buried silicide layers as well as the abruptness of the interfaces are studied by the RBS and channeling technique. The stability of the buried CoSi 2 layer at temperatures between 1000°C and 1200°C is also studied.

Ternary CoxFe(1−x)Si2 and NixFe(1−x)Si2 formed by ion implantation in silicon

Co1−xFexSi2 and Ni1−xFexSi2 metastable ternary phases were formed by sequentially implanting Co, Ni, and Fe into Si (111) at 623 K. In order to compare the phases formed by ion implantation, the Ni1−xFexSi2 stable bulk ternary phase with a wide variety of x values was synthesized. The samples were studied by Mossbauer effect, transmission electron microscopy (TEM), x-ray diffraction, and Rutherford backscattering and channeling. X-ray diffraction and TEM results on the as-implanted samples with x=0.5 indicate a cubic (fluorite) structure. 57Fe Mossbauer spectra show three resonanceline components. Comparison of the isomer shift values of the components with those measured in the stable and metastable transition-metal silicide phases indicated three different sites for iron atoms: Fe substituting Co or Ni; Fe in the empty cubes of the fluorite-type lattices; and Fe populating sites in the CsCl-type B2 lattice. In samples of Ni1−xFexSi2 annealed at 1273 K, α-FeSi2 and a fraction of Fe dissolved in NiSi2 app...

The formation and thermal stability of ion-beam-synthesized ternary MexFe1−xSi2 (Me=Co, Ni) in Si(111)

Abstract Buried CoxFe1−x and NixFe1−x silicides were prepared by consecutive metal implantation in Si(111). Transmission-electron microscopy analysis shows strong evidence for the formation of metastable ternary Co0.5Fe0.5Si2 and Ni0.5Fe0.5Si2 precipitates during implantation, the lattice structure of which is believed to be mainly B-type oriented (twinned) CaF2. Annealing of the samples at 1000°C results in coalescence of the silicide into continuous layers with sharp interfaces. During this high-temperature treatment, nearly full phase separation occurs in the case of Co0.5Fe0.5Si2, whereas for Ni0.5Fe0.5Si2 only the onset of phase separation is observed. Channeling spectrometry indicates a good alignment of the silicides with the substrate. Furthermore, all samples were studied with X-ray diffraction and Mossbauer spectrometry, in order to obtain detailed information on the strain and the phases present.