Temperature-Dependent Characteristics of GeSn Waveguide p-i-n Photodetectors: Step Towards Cryogenic Silicon Photonics

GeSn waveguide photodetectors (WGPDs) that function in the 2-μm band have been considered potentially competitive candidates for cryogenic silicon photonics to enable various emerging applications such as quantum sensing and quantum computing. Herein, we present a high-performance GeSn rib WGPD that can function within the 2-μm spectral range and its temperature-dependent characteristics. The proposed detectors feature a GeSn active layer with 4.9% Sn which redshifts the cutoff wavelength to cover the 2-μm band. In addition, the optical confinement factor was enhanced by growing a thick GeSn active layer. This resulted in a room temperature responsivity of 0.224 A/W at <tex-math notation="LaTeX">λ \ = \ 1900\ nm</tex-math> . We measured a noise equivalent power of <tex-math notation="LaTeX">9.5 × 10- 10\ W/Hz1/2</tex-math> at <tex-math notation="LaTeX">λ \ = \ 1550\ nm</tex-math> , confirming the practical viability of the proposed detector. Moreover, the temperature-dependent characteristics indicate that the dark current density ( <tex-math notation="LaTeX">J_dark\</tex-math> ) variation is extremely low and responsivity decreases at low temperatures, leading to decreased spectral detectivity ( <tex-math notation="LaTeX">D^*</tex-math> ), whereas the cut-off wavelength ( <tex-math notation="LaTeX">λ c</tex-math> ) blueshifts owing to the increased bandgap. The temperature-dependent characteristics of the proposed GeSn WGPDs are expected to advance the understanding of GeSn WGPDs for cryogenic silicon photonics.