Single photon avalanche detectors (SPADs) operating in gated-Geiger mode at near infrared wavelengths have applications in quantum key distribution (QKD), eye-safe light detection and ranging (LIDAR), 3D image sensing, quantum enhanced imaging and photonic based quantum information processing. Whilst InGaAs SPADs are commercially available, the high cost and lack of integrated SPADs limit the applications. We have previously demonstrated vertical Geiger mode Ge on Si SPADs at 1310 and 1550 nm operating at 100 K where the Ge is used as an absorber and the lower noise Si is used as the avalanche gain region. At 100 K and 1310 nm a single photon detection efficiency of 4% was demonstrated with a dark count rate (DCR) of 5 MHz.
Here we present first results on Ge on Si SPADs grown on top of silicon-on-insulator (SOI) substrates. Both vertical photodetectors and waveguide coupled detectors were investigated with designs aimed to reduce the DCR over previous results. Waveguides and avalanche regions were patterned in the top Si of a SOI wafer before being coated with silicon dioxide. Holes were then etched in the oxide to allow selective area growth of Ge inside these windows and on top of the Si waveguides for the waveguide coupled Ge SPADs. This approach reduces the threading dislocation density compared to bulk Ge growths which aids the reduction of the DCR. The fabricated devices have been tested at both 1310 nm and 1550 nm wavelengths and demonstrate improved performance over previous published results.
Emanuele Alberto Ghisetti, Derek Dumas, Jarosław Kirdoda, Kevin Gallacher, Ross William Millar, Muhammad M. A. Mirza, and Douglas J. Paul, "Germanium on silicon single-photon avalanche detectors using silicon-on-insulator substrates (Conference Presentation)," Proc. SPIE 10535, Integrated Optics: Devices, Materials, and Technologies XXII, 105351F (Presented at SPIE OPTO: February 01, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290403.5751551028001.
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