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.