Photoelectron spectroscopy study of GeSn epitaxial layers for photonic applications

We have investigated with X-ray Photoelectron Spectroscopy (XPS) the impact of different wet cleanings on the surface of thick GeSn 13% direct band-gap layers grown on germanium strain relaxed buffers. The XPS time-dependent study showed a fast Ge re-oxidation after only a few minutes, while tin was more stable. A dip in (NH4)2S after the 5 min surface treatment with HCl/HF (1% / 10%) slowed germanium re-oxidation. Optimized surface cleanings enabled us to investigate GeSn band structure by momentum-resolved Photo-Emission Electron Microscopy (kPEEM). The obtained band structure images of an ex-situ prepared GeSn 13% surface were discussed.