Integrated Heteroepitaxial Photodetectors

Abstract

Optical detection in the near-infrared and telecommunication bands has historically been performed using single-crystal bulk Ge, but the development of Ge-on-Si epitaxy reduced fabrication costs and opened doors for usage in applications including optical communications and infrared imaging. To reap the benefits of monolithic integration and incorporation in the back-end-of-line (BEOL) stack, low processing temperatures (< 450°) are required. Using novel processing methods and strategic anneals, we have demonstrated that low temperature Ge growths on silicon can achieve low defect densities required for high performance. In this work, Ge-on-Si p-i-n photodetectors illuminated under normal incidence have demonstrated comparable responsivity and dark current density to devices processed at high temperatures. Relatively low temperature anneals (500°C) increased performance, but as-grown diodes also showed a responsivity of 0.11 A/W and [formula]. Annealing conditions of 500°C 3 hr improved such performance to 0.15 A/W and [formula].

In the mid-wave infrared (MWIR), photodetection has been successfully implemented for decades using the II-VI material set, Hg₁₋ₓCdₓTe. Extensive research pushed HgCdTe to nearly reach its theoretical performance limit, while also highlighting its inherent shortcomings for commercialization. An upcoming material set, [formula] has the potential to overcome such barriers while promising comparable performance. In this work, Lumerical simulations were performed to optimize a waveguide-integrated photodetector that incorporated an [formula] homojunction and was straightforward to fabricate, assuming successful epitaxy growths. The photodetector design promoted 30% light absorption after 20 𝜇m propagation into the detection region.