Fig. 1. RSM around the asymmetric (−2  −2   4) reflection of (a) sample A; (b) sample B; (c) sample C; (d) sample D. The inset of (a) shows an schematic diagram of epitaxial structure of GeSn alloy. The inset of (c) shows an SEM image of sample C, and the positions marked by the red circle are the segregated Sn.

Fig. 2. Raman scattering spectra of GeSn samples and a Ge wafer for reference, and the position of the ball corresponds to the calculated Ge-Ge Raman shift.

Fig. 3. (a) Full view of XTEM image of sample D; inset: EDX Ge and Sn element mapping. (b) High-resolution XTEM image and FFT pattern of area “b” in (a). (c), (d) Inverse FFT images of the rectangular area in (b).

Fig. 4. SIMS profile of Sn composition and bandgap calculations at different depths of (a) sample A; (b) sample B; (c) sample C; (d) sample D. Regions marked with different colors correspond to different strain states of the RSM in Fig. 1.

Fig. 5. (a) Three-dimensional schematic of GeSn photodetector with interdigital electrode structure. The inset shows the top view of the device. (b) Working mechanism of GeSn photodetector under light incident conditions. (c) Dark I−V curves of GeSn photodetector at different temperatures. (d) Photocurrent spectra of the GeSn photodetector at 0.2 V for different temperatures.

Fig. 6. (a) Wavelength-dependent optical responsivity of GeSn photodetector under a bias voltage of 1 V at 77 K. Inset: responsivity at 3 μm as a function of voltage at 77 K. (b) Comparison of cutoff wavelength of GeSn photodetectors in different works.

Table 1. Summary of Growth Temperature (T_growth), Sn Crucible Temperature (T_Sn), Measured Sn Content (x), and Root Mean Square (RMS) Roughness of GeSn Samples^a

Table 2. Summary of the Performance of GeSn Photodetectors^a