Paper MI-ThM5
Heteroepitaxial Growth and Electronic Structure of Mn:Ga₂Se₃ Thin Films on Si(100):As: Exploration of a Candidate Dilute Magnetic Semiconductor

Thursday, October 18, 2007, 9:20 am, Room 619

Magnetic thin film semiconductors grown on nonmagnetic semiconductors (NMS) may provide a route to injection of spin polarized electrons into the NMS. The lack of magnetic materials with both a high Curie temperature and spin-preserving transport into electronic materials (e.g., silicon) is currently the primary obstacle to the development of useful spintronic devices. A relatively unexplored class of dilute magnetic semiconductor is transition metal doped III-VI semiconductors. Group III-VI semiconductors such as Ga₂Se₃ have intrinsic vacancies which lead to highly anisotropic growth, and which may lead to a high degree of magnetic anisotropy if the films can be made ferromagnetic through suitable doping. Scanning tunneling microscopy (STM), low energy electron diffraction (LEED) and photoemission spectroscopy (PES) have shown the addition of small quantities of manganese, about one percent, has a pronounced effect on the growth morphology and electronic properties of Ga₂Se₃ on arsenic passivated Si(100). Co-deposition of Mn and GaSe on Si(100):As results in tall, highly anisotropic, rectangular, Mn-rich islands with edges parallel to the [011] and [0-11] substrate crystal directions. Deposition of a pure Ga₂Se₃ layer before the doped material results in a different and more laminar structure. While islands still form, these islands are much shorter and wider with seemingly random shapes subject to the constraint that every piece of the perimeter lies along the same two crystal directions. These two structures can be easily distinguished by their LEED patterns where the first case shows 1x1 spots with streak features characteristic of the undoped Ga₂Se₃ structure, whereas the second case transitions to clear 1x1 spots with no other features. The effect of small concentrations of Mn on the band structure of thin film Ga₂Se₃ is equally pronounced. The Mn doping adds a new peak in the valence band about 4.2eV below the Fermi level, an area where pure Ga₂Se₃ has a low density of states.

This work was supported by NSF grant DMR 0605601. TCL acknowledges support from NSF/NCI IGERT DGE-0504573. Some of the research was pursued at the Advanced Light Source, which is supported by the DOE under contract DE-AC02-05CH11231.