High-Efficiency Broadband Infrared Thin-Film Germanium Photodetector Enhanced by a Resonant Cavity and a Nano-Slit Metasurface

Abstract

This paper presents a novel design for high-quantum-efficiency and broadband Ge-on-Si photodetectors. The design entails placing a SiO2-filled nano-slit metasurface on a free-standing resonant-cavity enhanced (RCE) Ge structure to achieve high quantum efficiency in a broad spectral range of 1000–1600 nm. This design addresses the limitations of narrow resonance linewidths for conventional RCE devices with Fabry–Perot cavities. The SiO2-filled metasurface introduces diffraction and additional phase matching of the incident light field to horizontal guided modes, thus enhancing light coupling to the active region at non-resonance wavelengths of the Fabry-Perot mode. The device with this design exhibits an average quantum efficiency of 73.28 % in the 1000–1600 nm spectral range and a minimum quantum efficiency of approximately 60%, which is three times higher than a device without the metasurface structure. The quantum efficiency at around 1300 nm reaches 76.65%, and that at around 1550 nm reaches 98.69%. The estimated responsivity is 0.81 A/W and 1.23 A/W, respectively. For high-speed applications, a device comprising a Si spacer below a thin Ge layer of 600 nm thickness is aimed for operation at a bandwidth of 55 GHz. This device exhibits an average of 64.96% quantum efficiency with a minimum quantum efficiency of around 60%. Its peak quantum efficiency reaches 92.61% at around 1300 nm and 94.65% at around 1550 nm. The corresponding estimated responsivity is 0.98 A/W and 1.18 A/W, respectively. Both designs are innovative solutions for high-speed infrared photodetectors of high quantum efficiency over a broad spectral range.

Keywords

• Broad-bandwidth photodetectors
• Germanium photodetectors
• infrared photodetectors
• metasurface
• resonant-cavity enhancement (RCE)