The energy bandgap (E_g) of Ge effectively shifts toward lower energies by alloying with Sn atoms. Strain-relaxed (SR) GeSn layers with more than 8% Sn content assumes a direct bandgap and can be potentially used for highly-sensitive photodetectors for the short-wavelength infrared (SWIR) region (E_g<0.6 eV). However, the epitaxial growth of SR GeSn alloys with high crystalline quality is challenging due to the large lattice mismatch with both Si and SR Ge [1]. One method for fabricating SR GeSn is based on the growth of compressively strained GeSn layers on SR Ge and releasing the strain by selective Ge under-etching [2]. In this study, a suspended IR‑photodetector was fabricated using strain-relaxed Ge_0.9Sn_0.1 layer through microstructuring and Ge under‑etching.

The GeSn layers were grown on a Ge-buffered Si wafer [3] in a reduced pressure chemical vapor deposition tool using digermane and tin tetrachloride as Ge and Sn precursors. Two batches of detectors were fabricated; one based on GeSn on Ge and the other one based on suspended GeSn layers. Photolithography and ICP dry etching were used for patterning the detectors and the Ge underneath were removed by anisotropic selective etching using CF₄ gas. XRD and RBS measurements indicate Sn contents of more than 10% without any Sn out diffusion. Raman spectroscopy shows the strain relaxation through Ge under‑etching and layer release. The temperature dependence dependent photoluminescence spectra shown in Fig. 1 is in accordance with a direct band gap transitions of the GeSn layers around 0.5 eV. The effects of layer suspension on the absorption spectra and the photo response of the detectors will be discussed in the presentation.

Fig. 1) Temperature dependence photoluminescence spectra of GeSn layer with 12% Sn content

Acknowledgements:

This work was supported by the Swedish Foundation for Strategic Research (SSF) and Vetenskapsrådet (VR).

References:

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[2] S. Gupta, R. Chen, Y. Huang, Y. Kim, E. Sanchez, J. S. Harris, and K. C. Saraswat, Nano Letters 13 (8), 3783-3790 (2013).

[3] A. Abedin, A. Asadollahi, K. Garidis, P.-E. Hellström and M. Östling, ECS Trans. volume 75, issue 8, 615-621 (2016).