Modeling and Design of GeSn Avalanche Photodiodes With High Tin Content for Applications at 3.3 μm

We propose and compare two back-side illuminated GeSn avalanche photodiode (APD) mesa structures with 15% tin content operating at photon wavelengths up to 3.3 μm, suitable for applications like methane gas sensing and analysis of tampered olive oil. The two structures have different multiplication materials: a) silicon, which requires an additional Ge Strain-Relaxed Buffer (SRB) layer for high-quality GeSn growth; b) germanium, which is acting also as SRB layer. The latter design is innovative compared to the state-of-the-art and it proposed to: i) reduce the space charge region (SCR) width by avoiding a too thick Ge SRB, which is required for growing high-tin-content GeSn; ii) avoid one supplementary non-lattice matched heterojunction in the SCR. Physical models for GeSn are discussed for the most relevant parameters of APD design. Simulations are performed in the electrical and optical domains, for evaluating the main figures of merit of APDs and comparing the expected performances between the two designs. Finally, we present the modeling and design of a focalizing all-dielectric metalens, integrated on the detector back-side, for improving the photon collection efficiency at the same active volume size, thus improving the signal-to-noise ratio.