Suspended germanium membranes photodetector with tunable biaxial tensile strain and location-determined wavelength-selective photoresponsivity

A divergent microstructure was fabricated by complementary metal–oxide–semiconductor compatible processes on the central region of a Ge p–i–n photodetector to enhance the residual tensile strain. A tunable biaxial tensile strain of ∼0.22%–1.01% was achieved by varying the geometrical factors, and it was confirmed by Raman measurements and finite element method simulations. The suspended germanium membranes enhance the absorption across the C- and L-bands (1528–1560 and 1561–1620 nm) and extend the cutoff wavelength to ∼1700–1937 nm. The Ge absorption coefficient is enhanced by ∼4.2× to 2951 cm−1 at 1630 nm, which is comparable with that of In0.53Ga0.47As. Furthermore, due to the varying strain distribution on the Ge mesa, each photodetector presents the location-determined wavelength-selective photoresponsivity characteristics. This work offers a promising approach for adjusting the absorption spectra of the photodetector by harnessing geometrically amplified biaxial strain.