Germanium (Ge)-on-silicon photodetectors operate successfully in the telecommunications wavelength ranges centered at 1310 nm and 1550 nm (the C- and L-bands), respectively; however, the Ge direct bandgap of 0.8 eV severely limits its operation above 1550 nm, making these types of detectors not usable at L-band (1565 to 1625 nm) and U-band (1625 to 1675 nm) wavelengths.
To reach the L- and U-bands, researchers at the Chinese Academy of Sciences (Beijing, China) built on earlier research that demonstrated the efficacy of germanium-tin (GeSn) alloys for these longer telecommunications wavelengths. But even though small concentrations of Sn reduce the bandgap enough to cover all telecommunications windows as well as increase the C- and L-band absorption by a factor of ten, fabrication of GeSn detectors has proven difficult due to poor thermal stability of the alloy and the large lattice mismatch between GeSn and silicon. To overcome these challenges, the researchers grew GeSn photodetectors using CMOS-compatible solid-source molecular-beam epitaxy in a standard lithographic, dry-etching, and lift-off-metallization process. Responsivity of the resulting GeSn detector at 1310, 1540, and 1640 nm was 0.52, 0.23, and 0.12 A/W, respectively—two orders of magnitude better than previously fabricated GeSn photodetectors.
Contact Chunlai Xue at [email protected].