Resonant-Cavity GeSn Photodiode for Low-Noise SWIR Detection

The patent introduces an optical cavity dimension to enhance light absorption. By creating a resonant cavity structure with specific length and refractive index conditions, the light is confined and reflected multiple times through the Ge absorption layer, effectively increasing the interaction path length without increasing the physical thickness of the layer. This resolves the contradiction by adding an optical dimension rather than simply increasing material thickness.

The patent employs a composite structure combining Ge absorption layer with optical cavity components (mirrors, dielectric layers). This composite design leverages the high absorption coefficient of Ge at specific wavelengths while using the optical cavity to compensate for the low absorption at other wavelengths, achieving both extended spectral coverage and maintained absorption efficiency.

The patent systematically varies the Sn content in the GeSn alloy to precisely control the detection wavelength. By adjusting the Sn concentration parameter, the bandgap and absorption characteristics are tuned to match specific wavelength requirements (1550 nm, 2000 nm), enabling flexible spectral coverage while maintaining compatibility with existing semiconductor manufacturing processes.

The GeSn-based optical cavity detector serves multiple functions: it provides extended spectral coverage up to 2000 nm, maintains compatibility with CMOS fabrication processes, and achieves high absorption efficiency through the optical cavity enhancement. This multi-functional design reduces overall system complexity by integrating multiple capabilities into a single device structure.

Instead of increasing the physical thickness of the absorption layer, the patent introduces an optical cavity dimension that creates multiple optical paths. The light is reflected back and forth through the thin absorption layer, effectively increasing the absorption probability without increasing the material thickness, thereby avoiding the associated increase in dark count rate.

The optical cavity acts as an intermediary structure that enhances the interaction between light and the absorption layer. By introducing mirrors and dielectric layers as intermediaries, the light is confined and redirected multiple times through the absorption layer, achieving high absorption efficiency in a thin layer without the noise penalties of thicker materials.

The patent uses GeSn alloys with varying Sn content to achieve detection wavelengths up to 2000 nm while maintaining lattice compatibility with Si substrates. This parameter adjustment allows the detector to achieve InGaAs/InP-level performance in the SWIR regime while remaining compatible with standard Si CMOS fabrication processes.

The patent creates a composite structure combining GeSn absorption layer with Si-based optical cavity components. This composite design enables SWIR detection capability comparable to InGaAs/InP devices while maintaining full compatibility with Si CMOS manufacturing, avoiding the need for complex heteroepitaxial growth processes required for III-V materials.