Paper MI-ThM3
Room Temperature Ferromagnetism and Surface Morphology in Cr-doped Ga₂Se₃ Films on Si(001)

Thursday, October 23, 2008, 8:40 am, Room 206

The intrinsic vacancy semiconductor Ga₂Se₃, which may be grown epitaxially on Si, presents several interesting issues for the study of dilute magnetic semiconductors. Transition metal doping may lead to occupation of either vacancy sites or Ga sites in the lattice, which could lead to n- or p-type doping, respectively. The vacancy-induced anisotropy and wide bandgap (2.3 eV) may also lead to high Curie temperatures. To probe the interaction between magnetism, morphology, and free carriers in this new class of magnetic material, experimental investigations of Cr-doped Ga₂Se₃ epitaxially grown on Si(100):As have been pursued. Inclusion of Cr into the Ga₂Se₃ lattice results in new states at the Fermi edge, signaling a metallic structure, and the films are ferromagnetic at room temperature (though with a saturation moment about 1/4 of the low temperature value.) Scanning tunneling microscopy reveals formation of clusters within trenches whose shape and size depend on the Cr concentration and whether or not an undoped Ga₂Se₃ buffer layer is deposited first. Scanning Auger microscopy reveals a compositional difference between the clusters and the terraces surrounding them, with a larger Cr:Ga ratio in the clusters. We suggest this concentration difference, and the resultant strain and/or difference in chemical potential, may control the size and shape of the trenches surrounding the clusters. Work supported by NSF grant DMR-0605601 and NER-0508216. ENY was supported by an IBM Fellowship; TCL was supported by an IGERT Fellowship, NSF/NCI DGE 0504573. Some experiments were performed at the Advanced Light Source, Berkeley, supported by DOE contract DE-AC02-05CH11231.