In Situ Studies of Germanium-Tin and Silicon-Germanium-Tin Thermal Stability

Abstract

Sn-containing group IV semiconductors provide a rich playground to independently engineer the band structure and lattice parameter with a potential impact of a variety of silicon-based electronic and optoelectronic devices. The introduction of these metastable alloys in device fabrication raises a number of concerns regarding the possible degradation of their composition and structural properties during different processing steps. With this perspective, in this work we present detailed in situ and ex situ investigations of the thermal behavior of both Sn-rich binary and ternary alloys. We used low energy electron microscopy and photoelectron emission electron microscopy to examine in real time the evolution of surface structure and composition during thermal annealing. These in situ studies are augmented using several ex situ characterization techniques. These investigations unraveled unprecedented details about the phase separation in these two systems. Particularly, in Ge0.84Si0.04Sn0.12 annealing above 410 °C leads to the formation of randomly distributed Sn-rich particles which grow as the annealing temperature increases. Additionally, the binary alloy Ge0.88Sn0.12 seems to be relatively more stable as compared to the ternary alloy with the same Sn content. The Sn-rich particles in the former system are not randomly distributed, but they are found to follow a well defined pattern on the surface along the <110> direction. The mechanisms and regimes involved in the phase separation are also briefly presented.