Detection in the short-wave infrared (SWIR) offers advantages like reduced solar noise and improved atmospheric transmission. Avalanche photodiodes (APDs) are ideal for low-light detection due to internal gain. While silicon (Si) APDs have low noise, they can't effectively detect SWIR light. Germanium (Ge) is good for SWIR detection but suffers from high noise. Ge-on-Si structure offers benefits like SWIR operation and efficient multiplication. This study showcases room temperature operation of a linear-mode pseudo-planar Ge-on-Si APD with high responsivity, gain, and low noise at 1550 nm. Moreover, a 10-pixel linear array exhibits uniform performance, promising for SWIR detection for potential LIDAR application.
This talk shows the recent development of linear and Geiger-mode pseudo-planar Ge-on-Si avalanche photodiodes (APDs) in the short-wave infrared region. We demonstrate a 26 µm-diameter Ge-on-Si Geiger-mode APD with an extremely low noise-equivalent-power of 7.7 × 10−17 WHz−½ and a jitter value of 134 ± 10 ps at 1310 nm wavelength and at 100 K operating temperature. We demonstrate that a linear array of Ge-on-Si linear mode APDs comprising of 10 pixels shows high responsivity, highly uniform avalanche breakdown voltage and avalanche gain at 1550 nm wavelength and at room temperature.
KEYWORDS: Single photon avalanche diodes, Passivation, Design, Germanium, Silicon, Monte Carlo methods, Short wave infrared radiation, Ozone, Engineering, Diffusion
Single Photon Avalanche Diodes (SPADs) are semiconductor devices capable of accurately timing the arrival of single photons of light. Previously, we have demonstrated a pseudo-planar Ge-on-Si SPAD that operates in the short-wave infrared, which can be compatible with Si foundry processing. Here, we investigate the pseudo-planar design with simulation and experiment to establish the spatial contributions to the dark-count rate, which will ultimately facilitate optimisation towards operation at temperatures compatible with Peltier cooler technologies.
KEYWORDS: Single photon avalanche diodes, Electric fields, Monte Carlo methods, Short wave infrared radiation, Design and modelling, TCAD, Device simulation, Germanium, Silicon photonics
Single photon avalanche diodes (SPADs) are semiconductor photodiode detectors capable of detecting individual photons, typically with sub-ns precision timing. We have previously demonstrated novel pseudo-planar germanium-on-silicon SPADs with absorption into the short-wave infrared, which promise lower costs and potentially easier CMOS integration compared to III-V SPADs. Here we have simulated the dark count rate of these devices, using a custom solver for McIntyre’s avalanche model and a trap assisted tunnelling generation model. Calibration and fitting have been performed using experimental data and the results have highlighted areas in which the technology can be optimised.
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.
A series of AlAsSb p+-i-n+ and n+-i-p+ diodes with varying i-region thickness from 0.08μm to 1.55μm have been used to determine the temperature dependent impact ionization coefficients by performing avalanche multiplication measurements from 210K to 335K. The increase in electron and hole ionization coefficients as the temperature decreases is much smaller when compared to InAlAs and InP. This leads to a much smaller avalanche breakdown variation of 13mV/K in a 1.55μm p+- i-n+ diode. For a 10Gb/s InGaAs/AlAsSb separate absorption and multiplication avalanche photodiode (SAM-APD), the variation in breakdown voltage is predicted to be only 15.58 mV/K.
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.
This paper presents the electron and hole avalanche multiplication and excess noise characteristics based on bulk AlAs0.56Sb0.44 p-i-n and n-i-p homojunction diodes lattice matched to InP, with nominal avalanche region thicknesses of 0.6 -1.5 μm. From these, the bulk electron and hole impact ionization coefficients (α and β respectively), have been determined over an electric field range of 220-1250 kV/cm for α and from 360-1250 kV/cm for β for the first time. Excess noise characteristics suggest an β/α ratio as low as 0.005 for an avalanche region of 1.5 μm in this material, close to the theoretical minimum and significantly lower than AlInAs, InP, or even silicon. This material can be easily integrated with InGaAs for networking and sensing applications, with modeling suggesting that a sensitivity of -32.1 dBm at a bit-error rate (BER) of 1×10-12 at 10 Gb/s at 1550 nm can be realized. This sensitivity can be improved even further by optimizing the dark currents and by using a lower noise transimpedance amplifier.
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.
This paper presents the performance of 26 μm and 50 μm diameter planar Ge-on-Si single-photon avalanche diode (SPAD) detectors. The addition of germanium in these detectors extends the spectral range into the short-wave infrared (SWIR) region, beyond the capability of already well-established Si SPAD devices. There are several advantages for extending the spectral range into the SWIR region including: reduced eye-safety laser threshold, greater attainable ranges, and increased depth resolution in range finding applications, in addition to the enhanced capability to image through obscurants such as fog and smoke. The time correlated single-photon counting (TCSPC) technique has been utilized to observe record low dark count rates, below 100 kHz at a temperature of 125 K for up to a 6.6 % excess bias, for the 26 μm diameter devices. Under identical experimental conditions, in terms of excess bias and temperature, the 50 μm diameter device consistently demonstrates dark count rates a factor of 4 times greater than 26 μm diameter devices, indicating that the dark count rate is proportional to the device volume. Single-photon detection efficiencies of up to ~ 29 % were measured at a wavelength of 1310 nm at 125 K. Noise equivalent powers (NEP) down to 9.8 × 10-17 WHz-1/2 and jitters < 160 ps are obtainable, both significantly lower than previous 100 μm diameter planar geometry devices, demonstrating the potential of these devices for highly sensitive and high-speed imaging in the SWIR.
AlAs0.56Sb0.44 is a promising avalanche material which can be grown lattice-matched to InP and therefore use InGaAs as the absorption region in a Separate Absorption and Multiplication APD (SAM-APD). The electron and hole ionisation coefficients in this material are very dissimilar and our experiments show that this leads to AlAs0.56Sb0.44 having the lowest excess noise performance of any InP based material system (F = 2.2 at M = 40) reported to date. Simulations suggest that operation at 1550 nm and 25 GB s-1 with a sensitivity of -25.7 dBm is possible in a normal incidence SAM-APD.
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