Temperature-Dependent Raman Spectroscopy Analysis of Epitaxially Grown Ge0.91Sn0.09 on GaAs (001) Substrate

Abstract: We report on the epitaxial growth of Ge<inf>0.91</inf>Sn<inf>0.09</inf> alloy epilayers on a GaAs (001) substrate by low-temperature molecular beam epitaxy. Temperature-dependent Raman measurements were used to investigate the behavior and stability of Sn in Ge<inf>1–x</inf>Sn<inf>x</inf> grown on GaAs by examining the behavior of the longitudinal optical phonon modes originating from both the Ge<inf>1–x</inf>Sn<inf>x</inf> epilayers and the GaAs substrate. The Raman data reveals improved crystalline quality and increased Sn content in the Ge<inf>1–x</inf>Sn<inf>x</inf> epilayer as the temperature is increased from 100 to 580 K. However, at a temperature of about T = 620 K, the mobility and segregation of Sn in the Ge<inf>1–x</inf>Sn<inf>x</inf> epilayers dramatically increases. This behavior is similar to reports of Sn mobility and potential segregation from Ge<inf>1–x</inf>Sn<inf>x</inf> grown on both Ge and Si substrates, despite differences in atom chemistry between Ge<inf>1–x</inf>Sn<inf>x</inf> and the different substrates. Likely, the transition temperature for which Sn becomes mobile in Ge<inf>1–x</inf>Sn<inf>x</inf> is dominated by its dependence on the bonding between Ge and Sn and level of strain in the Ge matrix.