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Ion implantation can produce open volume defects in silicon by one of two
methods, either by H or He implantation followed by annealing to create a
band of nanocavities and also by direct implantation to reasonably high
doses, which results in a vacancy excess region at depths less than about
half the projected ion range. This paper reviews three interesting aspects
of open volume defects. In the first case, the very efficient gettering of
fast diffusing metals to nanocavities formed by H-implantation is
illustrated. In addition, the non-equilibrium behaviour of Cu3Si
precipitation and dissolution at cavities is examined. The second example
treats the interaction of irradiation-induced defects with nanocavities,
particularly preferential amorphisation at open volume defects and
subsequent cavity shrinkage. The final example illustrates the coalescence
of excess vacancies into small voids on annealing and the use of gettering
of Au to detect such open volume defects.
By first growing NiSi2 precipitates in a-Si and then irradiating with a 150 keV Si beam, we have studied ion beam induced epitaxial crystallization (IBIEC) of Si initiated at a-Si/NiSi2 precipitate interfaces. The growth shape and its temperature dependence are studied in-beam via in situ transmission electron microscopy. Interface roughening is evidenced. Preliminary results for the Co-Si system are also reported.
Mid-infrared intraband absorption in Ge/Si self-assembled quantum dots is reported. The self-assembled quantum dots are grown by ultra-high-vacuum chemical vapor deposition. The intraband absorption is observed using a photoinduced absorption technique. The mid-infrared absorption, which is in-plane polarized, is maximum around 300 meV. The absorption is attributed to a quantum dot hole transition between bound and continuum states. The absorption cross section is deduced from the saturation of the photoinduced intraband absorption. An inplane absorption cross section as large as 2 × 10−13 cm2 is measured for one dot plane.
In this work, we have investigated the reaction between Zr and SiGeC alloys after Rapid Thermal anneals performed at 800°C for 5 min. The interactions of the metal with the alloy have been investigated by X-Ray diffraction. Four crystal X-Ray diffraction was also performed to measure the residual strain in the epilayer. The final compound of the reaction is the C49- Zr(Si1-xGex)2 phase. The C49 film contains the same Ge concentration as in the as-deposited Si1-x-yGexCy layer. This suggests that no Ge-segregation occurs during annealing. Only a small strain relaxation is detected in the unreacted SiGe epilayer during the reaction. The addition of C in the epilayer prevents any strain relaxation. These results are in contrast with those observed in systems with Ti and Co, and show that the system Zr-Si-Ge is much more stable. Schottky barrier heights have been also measured: annealing leads to a slight decrease of the barrier without any degradation of the contact. The resistivity of the C49 film is about 80 μΩcm. These results indicate that Zr may be a good candidate for contacts on IV-IV alloys in term of thermal stability.
Crucial features of materials evolution due to ion beam irradiation are often revealed only through studies of process dynamics. We review some significant examples of such experiments performed over the last 25 years with the Orsay in situ facility: a transmission electron microscope setup (with temperature stages operating between 4 and 1000 K) on a medium energy (3–570 keV) ion beam line. New results on nanocavity evolution and metal silicide nanoprecipitates in Si are presented briefly.We show that CoSi2 nanoprecipitate growth is mainly due to the constant Co atom contribution from the ion beam, and CoSi2 platelet growth is the result of a three-dimensional to two-dimensional growth mode transition.
We report an in situ transmission electron microscopy (TEM) study of nanocavity
evolution in amorphous Si (a-Si) under ion beam irradiation. The size evolution of the
nanocavities was monitored during ion irradiation with Si or As at various temperatures
between 300 and 600 K. A linear decrease of the nanocavity diameter was found as the
ion fluence increased; it was much faster than its counterpart in crystalline
Si (c-Si). Here, the shrinkage rate depended on the irradiation-induced atomic
displacement rate. No significant temperature dependence was observed, confirming
that the irradiation-induced nanocavity shrinkage in a-Si is essentially due
to ballistic interactions, i.e., differs radically from that in c-Si.
Let V be an irreducible nonsingular algebraic surface, Y ⊂ V be an algebraic curve and P a point of Y. Suppose a sign distribution is given locally in a neighbourhood of P on some connected components of V — Y. We give an algorithmic criterion to decide whether this sign distribution is induced by a regular function or not. As an application, this criterion enables one to decide whether two semialgebraic sets can be locally separated or not.
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