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 $\lambda \ = \ 1900\ \text{nm}$ . We measured a noise equivalent power of $9.5 \times {10^{ - 10}}\ \mathrm{W}/\mathrm{H}{\mathrm{z}^{1/2}}$ at $\lambda \ = \ 1550\ \text{nm}$ , confirming the practical viability of the proposed detector. Moreover, the temperature-dependent characteristics indicate that the dark current density ( ${J_{{\rm{dark\ }}}}$ ) variation is extremely low and responsivity decreases at low temperatures, leading to decreased spectral detectivity ( ${D^*}$ ), whereas the cut-off wavelength ( ${\lambda _{\mathrm{c}}}$ ) 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.