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Characterization of stoichiometric surface and buried SiN films fabricated by ion implantation using extended xray absorption fine structure

The epitaxial growth of FeSi2 silicides was studied by using ion-beam epitaxial crystallization (IBIEC) of Fe-implanted Si(001) samples. By employing Rutherford backscattering/channeling spectrometry and transmission electron microscopy it was possible to determine that the IBIEC process produces a γ-, α-, and β-FeSi2 phase sequence, with increasing Fe concentration along the implantation profile. The critical concentrations for γ→α and α→β phase transitions are 11 and 21 at. %, respectively. A study of the thermal behavior of these phases shows that the γ- and α-FeSi2 are metastable with respect to the β-FeSi2 phase. The γ to β-FeSi2 transition starts at 700 °C via an Ostwald ripening process. In addition a 800 °C, 1 h anneal of high Fe concentration samples produces a complete α and γ to β-FeSi2 transformation. Finally, it is demonstrated that a regular or a rapid thermal annealing on Fe-implanted Si samples induces only the formation of a β-FeSi2 phase.

We report on the growth of self-assembled ternary InAsP quantum dots embedded into GaAs. A comparison between average sizes and recombination energies for different dot species (InAs, InAsP, and InP) confirms the formation of the ternary alloy islands. By carefully changing the growth conditions, we determined a global growth map for InAs, InAsP, and InP dots, showing that it is possible to tailor the optical characteristics of the InAsP species, thus covering the energy range between InAs and InP quantum dot emission.

We have investigated SiC layers produced by ion beam synthesis on Si͑111͒ substrates using different procedures. Bare Si͑111͒ and SiO 2 /Si͑111͒ structures were implanted with carbon at 40 keV up to a fluence of 4 ϫ 10 17 cm −2 at a temperature of 600°C. Postimplantation annealing was carried out at 1250°C for 2 h in pure O 2 or Ar ͑with 1% of O 2 ͒. A SiC layer was synthesized for all the procedures involving annealing under Ar. However, for the samples annealed under pure O 2 flux, only that employing implantation into the bare Si͑111͒ resulted in SiC synthesis. Rutherford backscattering spectrometry shows that, after annealing, the stoichiometric composition is obtained.Transmission electron microscopy measurements demonstrate the synthesis of cubic-SiC layers that are completely epitaxial to the Si͑111͒ substrate. However, there is a high density of nanometric twins, stacking faults, and also narrow amorphous inclusions of laminar shape between the crystalline regions. The procedure based on high temperature implantation through a SiO 2 cap, etching the cap off, 1250°C postimplantation annealing under Ar ambient ͑with 1% of O 2 ͒, and final etching has shown advantages from the point of view of surface flatness and increased layer thickness, keeping the same layer epitaxy and accurate composition.

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We report on the growth of quantum dot ͑QD͒ layers of InAsP alloys buried in GaAs by low-pressure metalorganic chemical vapor deposition. Ternary QDs were obtained by the addition of a PH 3 flux during the InAs QD growth, exhibiting recombination energies lying between those of InAs and InP QDs. The electronic properties of these QDs, as evaluated by photoluminescence spectroscopy, could be tailored by varying both the growth rate and the PH 3 flux for a constant AsH 3 flux. The morphology of these QDs was investigated by transmission electron microscopy from which the formation of an InAsP ternary alloy QDs was inferred. Based on electron microscopy results, the fundamental role of As incorporation on the morphology of and on the defect nucleation associated to InAsP QDs could be then evaluated. From this optical-structural combined analysis, we were able to identify the growth conditions that produce good quality InAsP QDs embedded in GaAs.

The magnetic character and the ordering process of ␥-FeSi 2 precipitates formed by Fe implantation into Si͑100͒ followed by ion-beam epitaxial crystallization ͑IBIEC͒ have been studied using the Mössbauer technique. Measurements performed at 4 K have shown no evidence of magnetic interaction indicating that the ␥-FeSi 2 phase is not of magnetic character. Conversely, conversion-electron Mössbauer experiments performed after the IBIEC procedure show basically the presence of a doublet, despite the cubic structure of the ␥-FeSi 2 precipitates. However, after 1 h of annealing at 600°C, a singlet, which before was barely recognizable, became more pronounced. The singlet-to-doublet proportion increases with increasing Fe concentration ͑2 at. %рC p р8.5 at. %͒, indicating that after annealing a better ordering in the␥-FeSi 2 precipitates is achieved. This ordering is obtained by an adequate combination of Fe-implanted concentration and thermal annealing. These studies have been complemented by Rutherford backscattering and/or channeling and transmission electron microscopy experiments. ͓S0163-1829͑96͒07540-6͔