Composition and Strain Evolution of Undoped Si0.8Ge0.2 Layers Submitted to UV-Nanosecond Laser Annealing

Abstract

Ultraviolet Nanosecond Laser Annealing (UV-NLA, XeCl laser, 308 nm, 145 ns) was performed on 30 nm-thick Si0.8Ge0.2 epitaxial layers. The various regimes encountered after single pulse UV-NLA are described and discussed, including submelt, SiGe layer partial and total melt, as well as melt beyond the SiGe epi-layer. Energy densities around 2.00 J/cm² and above led to the formation of pseudomorphic layers with strong Ge redistribution. Starting from uniform Si0.8Ge0.2 layers, Ge segregation towards the surface resulted in the formation of a Ge-rich surface layer with up to 55% Ge for 2.00 J/cm². Such pseudomorphic SiGe layers with graded composition and a Ge-rich surface layer may find some promising applications such as contact resistance lowering in doped layers.