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.
We present innovative planar geometry Ge-on-Si single-photon avalanche diode (SPAD) detectors. These devices provide picosecond timing resolution for applications operating in the short-wave infrared wavelength region such as quantum communication technologies and three-dimensional imaging. This new planar design successfully reduces the undesirable contribution of surface defects to the dark current. This has allowed for the use of large excess biases, resulting in a single-photon detection efficiency of 38% when operated at 125 K using 1310 nm wavelength illumination. A record low noise equivalent power of 2 × 10-16 WHz-1/2 was achieved, more than a fifty-fold improvement compared to the previous best Ge-on-Si mesa geometry SPADs when operated under similar conditions. These Ge-on-Si SPAD detectors have operated in the range of 77 K to 175 K, and we will discuss ways in which the operating temperature can be raised to that consistent with Peltier cooling. We will present analysis of Ge-on-Si SPADs, which has revealed much reduced afterpulsing compared with SPAD detectors in other material systems. Laboratory trials have demonstrated these Ge-on-Si SPAD devices in short-range LIDAR and depth profiling measurements. Estimations of the performance of these detectors in longer range measurements will be presented. We will discuss the potential for the development of high efficiency arrays of Ge-on-Si SPADs for the use in eye-safe automotive LIDAR and quantum technology applications.
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