Examining the Design Trade-offs of Ge-on-Si Single Photon Avalanche Diodes with Etched Photonic Crystals

Single photon avalanche diodes (SPADs) are semiconductor devices capable of detecting individual photons of light. These devices are therefore key for numerous quantum applications such as quantum key distribution, quantum imaging and sensing, and photonic based quantum computing [1]. Typically, these applications either require or benefit from operation in the short-wave infrared (SWIR) spectral region; enabling long range eye-safe operation in free space systems and compatibility with telecoms wavelengths for optical fibre-based technologies. Ge-on-Si SPADs have emerged as a candidate for single photon detection in the SWIR, with potential for significantly reduced cost compared to state-of-the-art InGaAs/InP devices due to Si foundry compatibility, which can also facilitate close integration with CMOS electronics [2]. However, to date, single-photon detection efficiencies have remained low at 1550 nm wavelength due to relatively thin Ge absorber layers and exacerbated by the cooling that is often required to reduce dark-count rates (DCRs), which blue-shifts the absorption.