Semiconductor based single-photon avalanche diode (SPAD) detectors are widely used in quantum technology applications, which focus on the arrival time of single photons. Using germanium as the absorption region in a Separate Absorption and Multiplication design solves the operating limitation beyond the spectrum range of silicon, i.e. typically at a wavelength of ~ 1000 nm. Our first-generation planar geometry Ge-on-Si single-photon avalanche diodes utilised a 1000 nm Germanium absorption region and showed extremely low noise-equivalent-power of 7.7 × 10−17 WHz−½ at a wavelength of 1310 nm. We demonstrate new structures designed to achieve high single-photon detection efficiency at a wavelength of 1550 nm.
Single-photon avalanche diode (SPAD) detectors are of significant interest for numerous applications, including light
detection and ranging (LIDAR), and quantum technologies such as quantum-key distribution and quantum information
processing. Here we present a record low noise-equivalent-power (NEP) for Ge-on-Si SPADs using a pseudo-planar
design, showing high detection efficiency in the short-wave infrared; a spectral region which is key for quantum
technologies and hugely beneficial for LIDAR. These devices can leverage the benefits of Si avalanche layers, with
lower afterpulsing compared to InGaAs/InP, and reduced cost due to Si foundry compatibility. By scaling the SPAD
pixels down to 26μm diameter, a step change in performance has been demonstrated, with significantly reduced dark
count rates (DCRs), and low jitter (134ps). Ge-on-Si SPADs were fabricated using photolithography techniques and
characterised using time-correlated single-photon counting. The DCR reaches as low as kilocount/s at 100K for excess
bias up to ~5%. This reduction in DCR enables higher temperature operation; e.g. the DCR of a 26μm diameter pixel
at 150 K is approximately equivalent to a 100 μm diameter pixel at 77 K (100s of kilocounts/s). These low values of
DCR, coupled with the relatively temperature independent single photon detection efficiencies (SPDE) of ~29% (at
1310nm wavelength) leads to a record low NEP of 7.7×10−17WHz−1/2. This is approximately 2 orders of magnitude
lower than previous similarly sized mesa-geometry Ge-on-Si SPADs. This technology can potentially offer a lowcost,
Si foundry compatible SPAD operating at short-wave infrared wavelengths, with potential applications in
quantum technologies and autonomous vehicle LIDAR.
We present a pseudo-planar geometry 26µm diameter Ge-on-Si single-photon avalanche diode (SPAD) detector with temperature insensitive single photon detection efficiency of 29.4% at 1310nm wavelength for applications including free-space LIDAR. A record low dark count rate of 104 counts/s at 125K at an excess bias of 6.6% is demonstrated, with temporal jitter reaching 134ps. The noise-equivalent power is measured to be 7.7x10-17WHz-12 which is a 2 orders of magnitude reduction when compared to comparable 25µm mesa devices. This device represents the state-of-the-art for Ge-on-Si SPADs, and highlights that these Si foundry compatible devices have enormous potential for SWIR single-photon applications.
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