Ultralow Dark Current Small-Sized Germanium Photodetectors With a Self-Forming Guard Ring Structure

The small-sized germanium (Ge) lateral photodetectors (PDs) with a ultralow dark current of 1.77 nA under −1 V at room temperature were first realized by implementing a self-forming guard ring on Ge-on-insulator (GOI) platform. Through electric field simulation and activation energy analysis, it was established that widening the guard ring effectively reduces the electric field on the PDs’ sidewall, thereby minimizing the surface leakage current. Optical characterization proved that appropriately increasing the guard ring width does not compromise the PDs’ responsivity. The PD exhibited a maximum responsivity of 0.48 A/W at 1550 nm, along with a high specific detectivity of $1.86\times 10^{{10}}$ cm $\cdot $ Hz $^{\text {1/2}}\cdot $ W $^{-{1}}$ under −1 V, comparable to commercial Ge PDs. These findings indicate that the proposed method holds great promise for producing compact Ge PD arrays with superior signal-to-noise ratio.