Effects of high-temperature thermal annealing on GeSn thin-film material and photodetector operating at 2 µm

•Ordered nanopatterns are formed on the surface of GeSn from high-temperature annealing (~700 °C).•Structural and optical properties of GeSn films before and after rapid thermal annealing are reported.•An increased photocurrent (>200%) is observed for the GeSn photodetector at an annealing temperature of 550 °C at 2-µm wavelength. Here, we explore the thermal stability of GeSn epilayers with varying Sn contents (3–10%) at an annealing temperature ranging from 300° to 750°C. It is found that ordered nanopatterns are formed on the surface of GeSn with Sn content of 8% without excessive Sn precipitation after thermal annealing at 700 °C. Despite being annealed at high temperatures, the GeSn maintains its crystal structure, which is confirmed by the X-ray Diffraction (XRD), Raman spectrum, and secondary-ion mass spectrometry (SIMS). The corresponding photocurrents of the photodetectors at the wavelength of 2 µm also indicate the crystal quality of the GeSn alloys does not deteriorate significantly after high-temperature annealing (675–700 °C). Meanwhile, the decrease of dark current with the enhancement of Ip/Id ratio (on-off ratio) indicates the improvement of detectivity of the photodetector due to the annealing process. Furthermore, the annealing temperature is optimized to 550 °C to achieve 200% enhancement of photocurrents of the GeSn photodetectors operated at 2 µm.