Ge instability and the growth of Ge epitaxial layers in nanochannels on patterned Si (001) substrates

Abstract

We report the Ge thermal instability against surface diffusion in extremely narrow channels isolated by SiO2 and demonstrate the selective growth of strain-relaxed Ge epitaxial layers in channels as narrow as 10 nm on patterned Si (001) substrates by a combination of low temperature growth and selective recrystallization using Ge melt and regrowth during a millisecond laser anneal. Filling narrow channels at high growth temperatures is prohibited by Ge outdiffusion due to the high Ge chemical potential in such narrow channels. The Ge thermal instability depends on the channel width and a critical channel width of 50 nm is extracted from our calculation and experimental results. The Ge surface diffusion rate is dominated by the surface diffusion activation energy barrier that is significantly enhanced by the adsorbed surface hydrides. At a low temperature below 450 °C, a hydride-terminated surface is maintained which increases the Ge surface diffusion barrier and retards the outdiffusion of the Ge adatoms, providing excellent channel filling. The resulting low crystalline quality can be restored with a millisecond laser melt and regrowth.