AVS 52nd International Symposium
    Surface Science Wednesday Sessions
       Session SS1-WeA

Paper SS1-WeA9
Intrinsic Vacancy-Induced Nanostructure of Al@sub 2@Se@sub 3@: Another New Silicon Compatible Chalcogenide Based Semiconductor

Wednesday, November 2, 2005, 4:40 pm, Room 200

Session: Surface Structure and Morphology Modification
Presenter: C.Y. Lu, University of Washington
Authors: C.Y. Lu, University of Washington
J.A. Adams, University of Washington
D.A. Schmidt, University of Washington
X. Li, University of Washington
Q. Yu, University of Washington
M.A. Olmstead, University of Washington
F.S. Ohuchi, University of Washington
Correspondent: Click to Email
Adding new functionalities, such as magnetism and spintronics, to existing silicon-based technology requires combining different crystalline materials with silicon through heteroepitaxy. One intriguing class of materials that is both structurally and chemically compatible with silicon is the Group-III-Selenide semiconductors, such as Ga@sub x@Se@sub y@ and Al@sub x@Se@sub y@. These materials have intrinsic vacancies that influence the film morphology and resultant crystalline structure during the heteroepitaxial growth, and may also be used to host dissimilar atoms, such as magnetic transition metals, to add unique functionalities. We report here in-situ scanning tunneling microscopy and photoelectron spectroscopy of aluminum-selenide (Al@sub x@Se@sub y@) heteroepitaxy on Si(111)-7x7 and As-terminated Si(100). Unlike Ga@sub x@Se@sub y@, which crystallizes into either a layered GaSe or defected zinc-blende Ga@sub 2@Se@sub 3@, Al@sub x@Se@sub y@ exhibits only one bulk structure: defected wurtize. We find heteroepitaxy of Al@sub x@Se@sub y@ on Si(111) results in hexagonal Al@sub 2@Se@sub 3@, likely wurtzite, but defected zinc-blende Al@sub 2@Se@sub 3@ is initially formed on As-terminated Si(100). The morphology of Al@sub 2@Se@sub 3@/Si(111) consists of triangular nanodots with single orientation, in contrast to the mixed orientation of layered GaSe on Si(111). For Al@sub 2@Se@sub 3@/Si(100):As, we observe oriented nanowire structures at low coverage, similar to low coverage Ga@sub 2@Se@sub 3@/As:Si(100)nanowires;@footnote 1@ hexagonal crystalline islands nucleate after 2-3 bilayers. In these first 2-3 layers, the spiral vacancy arrangement unique to the wurtize structure is altered to a linear array by the symmetry of Si(100)substrate. We propose that different symmetry and bonding of the substrate surfaces induces different configurations of vacancies, resulting in the distinct surface nanostructures. @FootnoteText@ @footnote 1@T. Ohta et al., Phys. Rev. Lett. 94, 116102 (2005).