Simulation of backside- illumination resonant cavity enhanced Ge photodetectors

With the rapid advancement of image sensor technology, devices are evolving toward multi-information sensing, particularly with an increasing demand for wavelength-discrimination capabilities. However, realizing compact and scalable multispectral sensors in the infrared region remains a significant challenge. This paper proposes a backside-illuminated resonant cavity enhanced germanium photodetector, aimed at achieving distinctive spectral responses and wavelength-selective absorption in the short-wave infrared range without the need for additional optical filters.Focusing on the technologically significant 1310 nm and 1550 nm bands, the absorption spectra of the device are systematically investigated using Lumerical FDTD simulation software. By modulating the thickness of the germanium layer within the structure, absorption peaks are precisely positioned near the target wavelengths. This approach achieves a synergy of high absorption efficiency and narrowband spectral selectivity through simple thickness engineering.Both front-illuminated and backside-illuminated configurations are comprehensively simulated and compared. The backside-illuminated structure, composed of an Al reflective layer, a Ge absorption layer, an SiO₂ intermediate layer, and a Si substrate, demonstrates superior optical confinement within the resonant cavity. In particular, it achieves high absorption exceeding 90% across the 1310–1550 nm wavelength range while maintaining stable and controllable spectral behavior. The results indicate that the absorption peak position can be accurately tuned within the 1310–1550 nm band by adjusting the Ge layer thickness, enabling precise wavelength-selective enhancement without additional filtering components. The findings provide an effective solution for compact, filter-free, and scalably integrated infrared wavelength-selective detectors, demonstrating promising potential for both industrial and consumer-grade infrared multispectral sensing applications.