CMOS Design of Ge-on-Si Single-Photon Avalanche Diode with Ultralow Noise and Jitter

We have proposed a modified structure called the “charge focusing” design of a single-photon avalanche diode, based on our previous work using TSMC's 0.18 μm HV CMOS technology. We have demonstrated that this modified structure can improve the electric field distribution in the photon absorption layer, which previously resulted in worse jitter performance. This modification enhances carrier collection efficiency and detector timing resolution, leading to better performance in various applications where the pre-modified structure had been used. Furthermore, we propose that the modified structure can also be combined with the Separate Absorption and Charge Multiplication (SACM) structure to achieve high photon detection efficiency at infrared wavelengths, by adding a Germanium (Ge) epitaxy layer on top of the silicon layer. Our simulations show that the charge focusing design brings many advantages, most notably reducing the electric field at the edge of the Ge layer in the SACM structure, which is commonly used in silicon photonic and CMOS technologies.