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Direct evidence for substitutional ion-implanted indium dopants in silicon
Abstract
Channeling and blocking effects of electrons and positrons emitted from ion-implanted radioactive In dopants in silicon have been utilized for lattice location of In in parts-per-million concentrations. A majority of In atoms occupies substitutional sites after implantation at room temperature. Defect recovery, which is observed after annealing at 700 K, increases the channeling effects. These results corroborate conclusions from previous Mössbauer studies on the same system under identical implantation conditions. The nature of the damage cascades of the individual implanted impurity probe atoms is discussed.
... Already in the as-implanted state at doses around 10 12 cm -2 , indium, which acts as an acceptor in Si, was found with a substitutional fraction of 50%. Following annealing at 923°C, the substitutional In fraction increased to 100% [6]. Earlier lattice location experiments using Rutherford backscattering (RBS) at much higher In doses (>10 14 cm -2 ) had, even after annealing, only achieved a maximum of 50% substitutional In [7]. ...
This paper reports on recent advances in the application of electron emission channeling to studies of the lattice location
of radioactive probe atoms in semiconductors. The introduction of position-sensitive electron detection has resulted in an
improvement in the experimental efficiency of this method by two orders of magnitude. Electron emission channeling now is
able to carry out detailed lattice location studies, and is especially interesting for cases where conventional ion beam lattice
location techniques cannot be applied due to a lack of sensitivity. Characteristic features of electron emission channeling
with position-sensitive detection are discussed and illustrated by results on the lattice location of Er in Si and GaAs, and
on the lattice sites and stability of implanted transition metals in Si.
Applications of radioactive ion beams produced at the ISOLDE facility for Mössbauer studies of probe atoms in solids are presented.
Examples are given for a site-selective incorporation on different substitutional sites in compound semiconductors by ion
implantation and thermal annealing of the radiation damage resulting from the implantation. The interactions of the probe
atoms with lattice defects created in the implantation process have been studied to elucidate likely causes for the site-selective
implantation mechanism. The technique has enabled to determine the electronic densities at electrically active substitutional
probe atoms, having shallow donor or acceptor states as well as states deeper in the band gap. The results are in good agreement
with theoretical results from local density calculations. Methodological aspects of the Mössbauer emission techniques employed
at ISOLDE are compared to alternative accelerator based techniques and the consequences of the application of different precursor
isotopes to the 57Fe Mössbauer isotope are treated in detail for 57Fe in silicon. Finally, results obtained for the magnetic hyperfine interactions of 5 sp impurities associated with vacancies
in ferromagnetic metals are discussed.
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