Lattice Sites and Stability of Implanted Er in FZ and CZ Si
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Recently, we reported on direct lattice location experiments of 167 Er using the emission channeling technique [13-15]. This experimental method makes use of the fact that charged particles emitted from radioactive isotopes in a single crystal experience channeling or blocking effects along crystallographic axes and planes. This leads to an anisotropic emission yield from the crystal surface, which depends in a characteristic way on the occupied lattice sites of the probe atoms. Following implantation of 167Tm (tl/ 2=9.25 d) with doses around 5-6x 1013 cm2, we found that the majority of the decay product 167mEr (2.27 s) occupies near-T sites in both FZ and CZ Si after annealing at 600'C [13]. While in FZ Si 167mEr was stable on near-T sites at 900'C [14], annealing CZ Si at this temperature considerably reduced the near-T Er fraction. In this contribution we first focus on the Er lattice location results from samples implanted with much lower doses (6xl0 2 cm2 at 60 keV). In the as-implanted state these experiments characterize the lattice sites of isolated Er, though in an environment which is still rich in defects resulting from the implantation process. Secondly, we report in detail on the 167muEr emission
channeling from both FZ and CZ Si following isothermal annealing at 900'C. While in this case always affects a mixture of Tm and Er, and lattice location of Er is done the thermal processing 167 167m Er, the chemical similarity of both rare earth elements should following the decay of Tm to allow us to draw conclusions on the behaviour of Er in Si. EXPERIMENT The angular-dependent emission yield of conversion electrons following the decay of 167Tm to 167Er was measured by position-sensitive Si pad detectors [17]. Detailed descriptions of this detection method and the experimental setup are to be found in Refs. [13-16]. Si samples implanted with 60 keV 167Tm at room temperature were produced at the ISOLDE facility at CERN. The characteristics of the investigated samples are listed in Table I. All of the samples were dipped in HF prior to implantation in order to remove native oxide layers. Two types of thermal processing were applied, either ex-situ vacuum annealing (
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