Mixed Zn and O substitution of Co and Mn in ZnO

Abstract

The physical properties of an impurity atom in a semiconductor are primarily determined by the lattice site it occupies. In general, this occupancy can be correctly predicted based on chemical intuition, but not always. We report on one such exception in the dilute magnetic semiconductors (DMS) Co-and Mn-doped ZnO, experimentally determining the lattice location of Co and Mn using β − emission channeling from the decay of radioactive 61 Co and 56 Mn implanted at the ISOLDE facility at CERN. Surprisingly, in addition to the majority substituting for Zn, we find up to 18% (27%) of the Co (Mn) atoms in O sites, which is virtually unaffected by thermal annealing up to 900 • C. We discuss how this anion site configuration, which had never been considered before for any transition metal in any metal oxide material, may in fact have a low formation energy. This suggests a change in paradigm regarding transition metal incorporation in ZnO and possibly other oxides and wide-gap semiconductors.

Direct observation of the lattice sites of implanted manganese in silicon

“…The lattice sites of 56 Mn were inferred from the angular dependence of the emission yield of its β − particles along various axial and planar directions. [17][18][19][20] As it turns out, even at low concentrations only a minority of Mn (< 30%) occupies in fact ideal substitutional sites, while the large majority forms more complex structures with implantation defects or p-type dopants. Our results not only clearly illustrate the difficulties in using ion implantation as means of substitutional Mn doping, but also shed light on the general interaction of Mn with defects and impurities in Si.…”

Evidence of N substitution by Mn in GaN

“…Together with our recent report on O-substitutional Mn and Co in ZnO, 6 these results suggest that anion substitution by 3d transition metals may be a general phenomenon in wide-gap nitrides and oxides. However, because it is both highly unexpected and difficult to detect with conventional techniques, anion substitution by transition metals may have so far passed undetected.…”

“…The technique is particularly suited in cases where significant fractions of the impurity atoms occupy more than one lattice site. For Mn impurities in particular, this multi-site lattice location capability has allowed us to locate a fraction of implanted Mn on the bond-centered (BC) interstitial site in Ge, 21 in anionsubstitutional sites (Oxygen sites) in ZnO, 6 as well as to unambiguously identify the interstitial Mn site in GaAs and quantitatively study its thermal stability. 22,23 Epitaxial thin films of wurtzite [0001] GaN grown on sapphire were implanted at room temperature with a fluence of 2×10 13 cm −2 of radioactive 56 Mn (t 1/2 = 2.56 h), at the on-line isotope separator facility ISOLDE at CERN.…”

“…Ga in GaN and Zn in ZnO), some reports suggest that this is not a general rule (see Ref. 6 for a recent discussion on ZnO).…”

Minority anion substitution by Ni in ZnO

“…6,[9][10][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.…”