Rapid-scan femtosecond ellipsometry of Si1-xGex and C60 crystalline films

Abstract

Recent studies have shown that the femtosecond optical response of semiconductors depends sensitively on, and can provide a quantitative indicator of, key sample imperfections such as implantation damage,1 defects induced by low growth temperature,2 nonuniform doping profiles,1 and interface roughness.1 In this paper, we use an unamplified colliding-pulse mode-locked (CPM) laser (λ = 620 nm) to obtain the femtosecond ellipsometric response in air of Si1-xjGex and C60 crystalline films, for which, to our knowledge, no previous femtosecond studies exist. We show that femtosecond response of Si1-x Gex grown epitaxially on Si depends sensitively on the depth of the strained SiGc/Si interface beneath the surface, while the response of C60 films depends on the degree of crystallinity as determined independently by x-ray diffraction. In each case, the femtosecond response of the samples of highest crystalline quality reveals the basic nonequilibrium bulk carrier dynamics, whereas the response of less perfect samples reveals alterations in carrier dynamics attributable to strained interfaces, alloy separation, or amorphization. A "rapid scan"·3 of pumpprobe time delay Δt provides rapid data acquisition. © 1992 Optical Society of America