We have studied the lattice location of implanted nickel in silicon, for different doping types (n, n + and p + ). By means of on-line emission channeling, 65 Ni was identified on three different sites of the diamond lattice: ideal substitutional sites, displaced bond-center towards substitutional sites (near-BC) and displaced tetrahedral interstitial towards anti-bonding sites (near-T). We suggest that the large majority of the observed lattice sites are not related to the isolated form of Ni but rather to its trapping into vacancy-related defects produced during the implantation. While near-BC sites are prominent after annealing up to 300-500• C, near-T sites are preferred after 500-600• C anneals. Long-range diffusion starts at 600-700• C. We show evidence of Ni diffusion towards the surface and its further trapping on near-T sites at the R p /2 region, providing a clear picture of the microscopic mechanism of Ni gettering by vacancy-type defects. The high thermal stability of near-BC sites in n + -type Si, and its importance for the understanding of P-diffusion gettering are also discussed.

We report on the lattice location of implanted Ni in ZnO using the β − emission channeling technique. In addition to the majority substituting for the cation (Zn), a significant fraction of the Ni atoms occupy anion (O) sites. Since Ni is chemically more similar to Zn than it is to O, the observed O substitution is rather puzzling. We discuss these findings with respect to the general understanding of lattice location of dopants in compound semiconductors. In particular, we discuss potential implications on the magnetic behavior of transition metal doped dilute magnetic semiconductors.Despite being extensively investigated for more than ten years, the existence of intrinsic room-temperature ferromagnetism in wide-gap dilute magnetic semiconductors (DMS), such as 3d transition-metal doped ZnO and GaN, remains a topic of intense debate. 1,2 ZnO doped with Ni (either during growth 3,4 or by ion implantation [5][6][7][8] ) is a good example of that, with similar magnetic behavior being ascribed to intrinsic ferromagnetic order in some cases, 3,5,6 and ferromagnetic secondary phases in others. 4,7,8 Since the magnetic behavior of a specific dopant-host combination is largely dependent on the material's local structure, the precise determination of the dopants' lattice location is crucial for the understanding of DMS materials. In ZnO doped with Ni (high doping regime, i.e. few atomic %) either during growth 9-11 or by ion implantation 6 , Ni has been found to substitute only the cation (Zn), based on extended X-ray absorption fine structure (XAFS) experiments. 6,9-11 Making use of β − emission channeling, we have also observed pure Zn substitution by 3d transition metals, namely Fe 12 and Cu, 13 in the very dilute regime (< 0.02 atomic %). However, for other 3d transition metals (Mn and Co) also in the very dilute regime, we have recently observed minority O substitution (∼ 20%), 14 which is remarkably unexpected based on the general understanding of lattice site preference of impurities in compound semiconductors. Such a dependence on transition metal impurity, without an obvious trend across the 3d series -for example, a clear dependence on atomic number Z: Mn (Z = 25), Fe (26), Co (27), Cu (29) -suggests the existence of an intricate underlying mechanism which is yet to be understood. Crucial for the formulation of such a mechanism is a comprehensive investigation of the conditions under which a) lino.pereira@fys.kuleuven.be anion substitution occurs, in particular, regarding which transition-metal/host combinations can accommodate it.Here, we report on β − emission channeling studies of the lattice location of implanted Ni (Z = 28) in ZnO, in the very dilute regime (< 0.02 atomic %). Emission channeling 15 makes use of the charged particles emitted by a decaying radioactive isotope. The screened Coulomb potential of atomic rows and planes determines the anisotropic scattering of the particles emitted isotropically during decay. Since these channeling and blocking effects strongly depend on the initial position of...