Lattice location and thermal stability of implanted Fe in ZnO

Abstract

The emission channeling technique was applied to evaluate the lattice location of implanted 59 Fe in singlecrystalline ZnO. The angular distribution of β − particles emitted by 59 Fe was monitored with a position-sensitive electron detector, following 60-keV low dose (2.0×10 13 cm −2 ) room-temperature implantation of the precursor isotope 59 Numerous technological breakthroughs are envisaged with the use of magnetic semiconductor materials that show a ferromagnetic ordering temperature at or above room temperature, e.g., spin transistors, ultradense nonvolatile memories and optical emitters with polarized output [1]. One class of materials, which are especially promising for applications, are diluted magnetic semiconductors, usually ternary systems of the type III 1-x -TM x -V or II 1-x -TM x -VI, where a 3d transition metal (TM) partly substitutes up to a few per cent of the group III or group II cations. It has been predicted by theory that the III-nitride semiconductors GaN and InN and the II-oxide semiconductor ZnO are suitable hosts to exhibit ferromagnetism close to or above room temperature [2,3]. In the case of ZnO, besides V, Cr, Mn, Co and Ni, Fe should also act as a ferromagnetic dopant [3][4][5]. Several reports on ferromagnetic systems based on ZnO can be found in the literature [1,[6][7][8][9][10][11][12][13][14]. Cases in which no ferromagnetic behavior was observed [7,[15][16][17][18] revealed systematic trends for the various transition metals, doping concentrations, and differences between n-and p-type ZnO, but also conflicting results between different authors. It was thus argued [11,14] that experimental reproducibility needs to be improved. The exact nature of the ferromagnetism also remains unclear [1,8,11,13]; among possible problems are the formation of metallic TM or TM-oxide clusters [9,[12][13][14]17] or magnetism from the substrate on which thin films are deposited [18]. Two recent review papers on the subject concluded that a more precise control of the TM dopant in the oxide and careful structural and microstructural analyses are needed [1,11].Experimentally TM dopants have been introduced both during ZnO powder synthesis [10,14,16] and growth of epitaxial thin films [6][7][8][9]11,15,18]. In addition, ion implantation is also actively being explored for TM doping of ZnO [1,12,13,19]. With respect to implantation, the questions that should be clarified, are: to what extent are TMs incorporated into the proper lattice sites (substituting for Zn atoms), what is the microstructure of substitutional TMs, and what are the optimum annealing conditions.We have partly addressed some of these issues in a previous study on Fe-implanted ZnO [20], which, however, focused on its optical properties. In that case, 56 Fe was implanted at 100 keV up to a fluence of 10 16 cm −2 into ZnO single crystals, followed by Rutherford backscattering spectroscopy (RBS) analysis of the damage and its recovery during thermal annealing. Since Fe in ZnO cannot be detected by RBS, particle-induced X-ray emiss...

Lattice sites of implanted Cu and Ag in ZnO

“…We would like to remark that there also exist transition metals that show a different behaviour in ZnO. For instance, Fe was to nearly 100% incorporated on ideal substitutional Zn sites following vacuum annealing at 800°C and did not show similar large displacements as Cu or Ag even after annealing at 1050°C [25].…”

Mixed Zn and O substitution of Co and Mn in ZnO

“…In our previous EC experiments on 59 Fe:ZnO, the maximum fraction of Fe on substitutional O sites compatible with the experimental data is less than 5%, which is considered below the sensitivity limit of the technique. 18 The average β − energies for 61 Co and 56 Mn are 460 keV and 831 keV respectively, and are thus significantly larger than the one for 59 Fe, which is 118 keV. Since a higher β − energy results in narrower channeling effects, the experimental patterns from 61 Co and 56 Mn are less resolved than those previously measured for 59 Fe.…”

Emission channeling studies on transition-metal doped GaN and ZnO: Cation versus anion substitution

“…However, this does not explain why, under very similar experimental conditions, anion substitution does not occur for implanted Fe, both in GaN [21] and ZnO [22]. Just as Mn and Co, Fe is a 3d transition metal, with a similar atomic mass and, therefore, similar incorporation kinetics and defect creation.…”

“…We report β − emission channeling experiments on implanted Co in GaN and, together with our previous reports on implanted Co in ZnO [20] as well as Fe and Mn in GaN and ZnO [19][20][21][22], we discuss the technique's advantages in such cases of multi-site occupancy.…”