Robustness of Sn precipitation during thermal oxidation of Ge1−xSnx on Ge(001)

Abstract

The thermal robustness of Sn segregation and precipitation in epitaxial Ge1−xSnx layers on Ge(001) substrates with a Sn content greater than the equilibrium solubility limit has been investigated for applications of Ge1−xSnx in high-performance metal–oxide–semiconductor field-effect transistors (MOSFETs). Sn segregation and precipitation occur on the Ge1−xSnx surface after epitaxial growth of the Ge1−xSnx layer at 150 °C. After the thermal oxidation of the Ge1−xSnx layer below 500 °C, there are no significant decreases in the average Sn content in the Ge1−xSnx layer and no additional Sn segregation on the Ge1−xSnx surface. However, Sn precipitation occurs at the Ge1−xSnx surface during the thermal oxidation of the Ge1−xSnx layer with an average Sn content as high as 8.7% at 600 °C, causing a decrease in the Sn content in the Ge1−xSnx layer. The Sn content in the Ge1−xSnx oxide is 1.5 times greater than that observed near the Ge1−xSnx surface for the sample with a Sn content of 8.7% after the thermal oxidation at 400 to 500 °C. The capacitance–voltage characteristics of the Al/Al2O3/Ge1−xSnx/Ge MOS capacitors treated with thermal oxidation at 400 °C indicate that the slow state density increases with the Sn content. Meanwhile, the small interface state density could be achieved via thermal oxidation of the Ge1−xSnx layer, even with a high Sn content.