Planar geometry Ge‐on‐Si single-photon avalanche diode detectors for the short-wave infrared

The addition of germanium to Si-based single-photon avalanche diode (SPAD) detectors can significantly increase the spectral range of these devices into the into the strategically important short-wave infrared (SWIR) region. We present the performance characteristics of small area (26 μm and 50 µm diameter) planar geometry Ge-on-Si SPAD detectors. There are many advantages for operating such SPAD detection in the SWIR region, these include: reduced eye-safety laser threshold, longer measurable ranges, improved depth resolution in range finding applications; and improved capability for imaging through obscurants such as precipitation and smoke. The time-correlated single-photon counting (TCSPC) technique has been utilized for the measurement of record low dark count rates (DCRs) and high single-photon detection efficiency. Specifically, the 26 µm diameter devices maintained DCR values < 100 kHz up to a temperature of 125 K for excess biases up to 6.6 %. The 50 µm diameter device consistently demonstrated DCRs a factor of approximately 4 times greater than 26 µm diameter devices, under identical operating conditions of excess bias and temperature, illustrating a dark count rate in proportion to the device volume. Single-photon detection efficiencies were found to reach a maximum of ~ 29 %, measured at a wavelength of 1310 nm and a temperature of 125 K. Due the record low dark currents observed, noise equivalent power values (NEP) down to 7.7 × 10-17 WHz-1/2 are obtained, significantly reduced when compared to both previous mesa geometry and larger area planar geometry Ge-on-Si SPADs, indicating much improved optical sensitivity levels attainable with these planar geometry devices. In addition to this, high speed operation was demonstrated, quantified by jitter values down to 134 ± 10 ps at a temperature of 100 K. These results demonstrate the potential of these devices for highly sensitive and high-speed LIDAR imaging in the SWIR.