Abstract for 1999 American Vacuum Society Meeting
Seattle, WA  October, 1999

Title:  Surface Modification in Heteroepitaxy : Laminar, Crystalline
Silicon on CaF@sub 2@

Authors:
	Brett R. Schroeder, Shuang Meng, Aaron Bostwick, Eli Rotenberg and
		Marjorie A. Olmstead

Abstract:

CaF@sub 2@/silicon heterostructures are strong candidates for obtaining
visible light emission from silicon. However, the heteroepitaxial growth
of laminar, crystalline silicon on CaF@sub 2@(111) substrates is hindered
by two factors 1) CaF@sub 2@ surface energy is much lower than that of Si
and 2) a strong etching reaction between Si and F. We have overcome these
difficulties through surface modification 1) use of arsenic as a
surfactant 2) electron irradiation to remove surface fluorine. Low energy
(40 eV) electron irradiation removes fluorine (amount of F removed scales
linearly with the electron dose) but the films become extremely reactive
with oxygen and/or water vapor (even under UHV conditions). Arsenic
termination stabilizes this surface and serves as a surfactant for the
subsequent silicon growth. X-ray photoelectron spectroscopy shows Ca-Si
bonds at the interface and As-Si bonds at the surface. The silicon surface
has a bulk-like termination, characteristic of Si(111):As, as evidenced by
the 1X1 LEED pattern. X-ray photoelectron diffraction shows that the grown
silicon layer is crystalline, rotated 180@super o@ with respect to the
CaF@sub 2@ substrate (Type B interface), and completely covers the CaF@sub
2@. Supported by DOE grant DE-FG03-97ER45646/A002.