Physics – Condensed Matter – Materials Science
Scientific paper
Jan 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007phrvb..75a4438m&link_type=abstract
Physical Review B, vol. 75, Issue 1, id. 014438
Physics
Condensed Matter
Materials Science
12
Materials Science Applications, Magnetic And Electrical Properties, Experimental Aspects, Magnetic Fields And Magnetism
Scientific paper
In this paper, we describe a new growth technique realizing the simultaneous control of growth mode and ferromagnetic ordering in Co-doped ZnO layers. Remarkable changes in growth occurred as a result of doping with Co ions. Exposure to O2 plasma to generate an oxygen-rich atmosphere was indispensable for the fabrication of undoped ZnO layers given stabilization of the negatively charged growing surface in a two-dimensional (2D) mode. In contrast, the 2D mode of Zn0.94Co0.06O layers was adequately retained in the absence of a plasma source, and was attributable to the covalence provided by the 3d character of Co ions compared with the 4s character of Zn ions. Spontaneous magnetization of Zn0.94Co0.06O layers was closely correlated with the number of free electrons, which was controlled by the activation energy of donor levels. This was also confirmed for O-polar Zn0.94Co0.06O layers. Ferromagnetic (FM) ordering was observed at ne values close to the Mott transition and led to hopping conduction between shallow donor bands. However, levels of p(O2) below 10-6mbar that yielded FM ordering generated a pitted surface and led to crystalline deterioration. Given our understanding of the formation mechanism of pits, we applied a periodic oxygen pressure-modulated epitaxy that resulted in the coherent growth of Co-doped ZnO layers with a 2D mode. This specific growth was effective in producing pit-free surface uniformities over large areas that maintained FM ordering.
Matsui Hiroaki
Tabata Hitoshi
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