High performance germanium on silicon photodiodes for back-end-of-line photonic integration

Abstract

Integration of near-infrared photodetectors in the back-end-of-line requires low temperature growth of Ge (<450 °C). We have fabricated high performance, vertical incidence Ge-on-Si photodiodes under thermal budget constraints with as-grown diodes achieving an internal quantum efficiency (IQE) of 38% and a dark current density of Jd = 272 μA/cm2 at a reverse bias of Vr = 5 V and a wavelength of λ = 1310 nm. The photodiode design incorporates a remote heterointerface, demonstrating that Ge material quality is sufficiently high for minority carriers to diffuse to the Ge/Si interface. Post-growth annealing improves device performance, including 500 °C 3 h exposure that improves IQE to 57% and Jd = 165 μA/cm2. Low-temperature grown Ge-on-Si photodiodes give comparable performance to diodes processed at high temperatures despite thermal budget constraints.