AVS 51st International Symposium
    Semiconductors Tuesday Sessions
       Session SC-TuA

Paper SC-TuA4
Molecular Beam Epitaxy of High-quality Ge on Si by Self-directed "Touchdown" of Nanoscale Seed Pads Through a Thin SiO2 Layer

Tuesday, November 16, 2004, 2:20 pm, Room 304C

Session: Semiconductor Heteroepitaxy and Nanostructures
Presenter: S.M. Han, University of New Mexico
Authors: Q. Li, University of New Mexico
D. Leonhardt, University of New Mexico
Y.B. Jiang, University of New Mexico
H. Xu, University of New Mexico
S.R.J. Brueck, University of New Mexico
S. Hersee, University of New Mexico
S.M. Han, University of New Mexico
Correspondent: Click to Email
Growing a lattice-mismatched, dislocation-free epitaxial film on Si has been a challenge for many years. Herein, we exploit nanoheteroepitaxy to grow high-quality Ge epilayer on Si. A 1.2-nm-thick chemical SiO@sub 2@ film is produced on Si in a H@sub 2@O@sub 2@ and H@sub 2@SO@sub 4@ solution. When the chemically oxidized Si substrate is exposed to Ge molecular beam, relatively uniform-size nanoscale seed pads form in the oxide layer and "touch down" on the underlying Si substrate. Although the "touchdown" location is random, the seed pad growth is self-limiting to 7 nm in size. Upon continued exposure, Ge selectively grows on the seed pads rather than on SiO@sub 2@, and the seeds coalesce to form an epitaxial lateral overgrowth (ELO) layer. The Ge ELO layer is characterized by high-resolution, cross-sectional transmission electron microscopy (XTEM), Raman spectroscopy, and etch-pit density (EPD). The XTEM images reveal that the Ge ELO layer is free of dislocation network and that the epilayer is fully relaxed at 2 nm from the heterojunction. The Raman shift of Ge optical phonon mode exactly matches that of relaxed bulk Ge, further supporting that the ELO layer is fully relaxed. The XTEM images, however, show that stacking faults exist near the Ge-SiO@sub 2@ interface. A small fraction (~4x10@super -3@%) of these stacking faults propagate to the epilayer surface and form etch pits, when immersed in a solution containing HF, HNO@sub 3@, glacial acetic acid, and I@sub 2@. The resulting EPD is consistently less than 2x10@super 6@ cm@super -2@. The reduction of strain density near the Ge-Si heterojunction, leading to high quality Ge ELO layer, is mainly attributed to a high density (~10@super 11@ cm@super -2@) of nanoscale Ge seed pads interspaced by 2- to 12-nm-wide SiO@sub 2@ patches. This "touchdown" technique may potentially enable growing other highly lattice-mismatched epilayers on Si, such as GaN and SiC.