A.-M. Van Bavel

Low‐temperature anneal of the divacancy in p‐type silicon: A transformation from V2 to VxOy complexes?

Deep level transient spectroscopy of electron irradiated p‐type silicon reveals a defect level at Ev+0.19 eV, which during anneal treatments at 200 °C gradually transforms into a band with Ev+0.24 eV. Both energy levels however, are reported in literature to be the donor level of the divacancy. In the present study it is proposed that during the low‐temperature anneal the divacancy interacts with oxygen, forming a V2O complex. During heat treatments at temperatures in the range between 250 and 450 °C a further shift of the deep level to higher energy positions is observed which might be related with other vacancy‐oxygen complexes.

Influence of oxygen and carbon on the generation and annihilation of radiation defects in silicon

Abstract The influence of oxygen and carbon on the generation and annihilation of radiation defects in silicon is studied by deep level transient spectroscopy (DLTS), correlated with photoluminescence (PL) analyses. N + p silicon diodes with interstitial oxygen content between 10 16 cm −3 and 10 18 cm −3 and carbon content below 10 16 cm −3 , are irradiated by 2 MeV electrons with fluences ranging from 5 × 10 14 cm −2 to 10 16 cm −2 . The DLTS spectra reveal two hole traps characterised by an activation energy of respectively 0.19 eV and 0.36 eV. Correlation with PL measurements confirmed the association of the 0.36 eV level with a C i O i and/or C i C s complex. Isothermal anneals performed at 200 °C resulted in a gradual conversion of the E v + 0.19eV to a defect level at E v + 0.24eV. From the oxygen content dependence of the transformation it is suggested that the divacancy diffuses and is trapped by interstitial oxygen forming a V 2 O complex.

Growth and properties of ion beam synthesized Si/CoxNi1−xSi2/Si(111) structures

Heteroepitaxial CoxNi1−xSi2 layers with good crystalline quality (χmin=3.5%) have been formed by ion beam synthesis. For a sample with x=0.66, we found that this ternary silicide layer contains 11% type B and 89% type A orientation. The transmission electron microscopy investigation reveals that the type B component is mainly located at the interfaces and with a thickness of only a few monolayers. X‐ray diffraction studies of the sample show that the strain of the type B component is smaller than that of the type A and is probably the reason for such a unique distribution of the type B component in the epilayer. Rutherford backscattering‐channeling, Auger electron spectroscopy, transmission electron microscopy, and x‐ray diffraction have been used in this study.

Implantation temperature dependent distribution of NiSi2 formed by ion beam synthesis in silicon

The formation and distribution of NiSi2 in (111) silicon by Ni‐ion implantation with a fluence of 1.1×1017 cm−2 and an energy of 90 keV is studied as a function of the temperature during implantation. For temperatures below 200 °C, a buried layer of NiSi2 precipitates is formed. Increasing the temperature gradually from 200 to 350 °C leads first to the formation of a double buried NiSi2 layer which with increasing temperature evolves into an epitaxial NiSi2 surface layer. A tentative model to explain for the observed anomalous behavior is presented.

Structural characterization of ion‐beam synthesized NiSi2 layers

NiSi2(111) and NiSi2(100) layers with good crystalline quality have been formed by ion‐beam synthesis. An unusual Ni atom distribution showing two completely separated layers during a single implantation step has been observed by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). The orientation, strain, and stiffness of the NiSi2 layers have been studied by RBS/channeling, x‐ray diffraction, and TEM. The results show that the continuous NiSi2 layers have type‐A orientation with a parallel elastic strain larger than the theoretical value of 0.46% for pseudomorphic growth. The perpendicular strain of the NiSi2(111) layers is apparently smaller than that of NiSi2(100) layers, indicating a higher stiffness in the 〈111〉 direction.

Simultaneous synthesis of well-separated buried and surface silicides using a single ion implantation step

An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300 °C, with a dose of 1.1×1017/cm2 and at a fixed energy of 90 keV. RBS/channeling, AES, and cross‐sectional TEM have been used to study this phenomenon as a function of the substrate temperature and Co co‐implantation. A model is presented, based on the diffusion of the transition metal, the defect annealing during the implantation, and the gettering power of the surface and the end of range defects.

Mono- and Binuclear Iron Complexes in Zeolites and Mesoporous Oxides as Biomimetic Alkane Oxidation Catalysts

Many enzymes [1–10] successfully catalyse the oxidation of alkanes, even the most inert ones such as methane. The precise architecture of their active site allows such catalytic properties. Such an active site contains a dinuclear iron core, in which μ2-O or μ2-OH bridging is observed. The environment in which the active site is embedded e.g. the protecting protein matrix, adds to the substrate specificity of the enzyme. Apart from the dinuclear iron active site, proximal functions such as catalytic initiators e.g. tyrosyl-radicals, help to establish long range, proton coupled electron transfer chains. Furthermore the interactions between enzymatic subunits add to the complexity of these systems.

Mossbauer search for co-acceptor pairs in si

Abstract Mossbauer spectroscopy was used to study the formation and stability of Co-acceptor complexes after diffusion of 57Co in heavily B-, Al-, Ga- and In-doped silicon. The 57Fe MS-spectra recorded after diffusion and quench show a dominating line complex (with an absorber isomer shift between + 0.7 and + 1.0 mm s relative to α-Fe), previously attributed to Co-acceptor pairs. Upon annealing a transformation of this Co-complex is observed, and activation energies are derived in the range of 1.4 to 1.8 eV, much larger than expected for the dissociation of Co-acceptor pairs. Possible reasons for this discrepancy are discussed.

Ion beam synthesis of buried and surface nickel silicides during a single implantation step

Abstract An unusual Ni distribution with two completely separated buried and surface silicide layers has been observed after Ni ion implantation in Si(111) kept at a temperature of 300°C, with a dose of 1.1 × 10 17 /cm 2 and at a fixed energy of 90 keV. The Ni profile and its substrate temperature dependence, its dose dependence and the influence from the preceding Co implantation were studied by RBS, AES and TEM. A model based on the diffusion of the transition metal, defect annealing during the implantation, and the gettering power of the surface and the end-of-range defects is presented.

Low Temperature Annealing Studies of the Divacancy in P-Type Silicon

In the present study an Ev+0.19 eV deep level is observed in boron doped Si after electron irradiation at room temperature. After prolonged anneals at temperatures between 200 and 300°C a gradual shift of the deep level with annealing time occurs however towards Ev+0.24 eV. The observed transition is much faster in Cz than in FZ silicon suggesting the involvement of oxygen. It is shown that this apparent gradual shift of the deep level in the bandgap can be explained by a gradual transformation of the divacancy with trap parameters (Ev+0.17 eV, capture cross-section σ∼1017 cm2) towards another defect with trap parameters (Ev+0.24 eV, ˃∼1015 cm2). The final defect is assumed to be a multi-vacancy/oxygen complex. First results are presented of an electron paramagnetic resonance (EPR) and infrared (IR) spectroscopy study before and after the transition to confirm this hypothesis.