Temperature-Dependent Characteristics of GeSn Waveguide p-i-n Photodetectors: Step Towards Cryogenic Silicon Photonics
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Abstract
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 <inline-formula><tex-math notation="LaTeX">$\lambda = \text{1900 nm}$</tex-math></inline-formula>. We measured a noise equivalent power of <inline-formula><tex-math notation="LaTeX">$9.5 \times {{10}^{ - 10}}\ \mathrm{W}/\mathrm{H}{{\mathrm{z}}^{1/2}}$</tex-math></inline-formula> at <inline-formula><tex-math notation="LaTeX">$\lambda = \text{1550 nm}$</tex-math></inline-formula>, confirming the practical viability of the proposed detector. Moreover, the temperature-dependent characteristics indicate that the dark current density (<inline-formula><tex-math notation="LaTeX">${{J}_{{\rm{dark }}}}$</tex-math></inline-formula>) variation is extremely low and responsivity decreases at low temperatures, leading to decreased spectral detectivity (<inline-formula><tex-math notation="LaTeX">${{D}^*}$</tex-math></inline-formula>), whereas the cut-off wavelength (<inline-formula><tex-math notation="LaTeX">${{\lambda }_{\mathrm{c}}}$</tex-math></inline-formula>) 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.