Krystyna Slomkowski

Advances in InGaAsP-based avalanche diode single photon detectors

In this Topical Review, we survey the state-of-the-art of single photon detectors based on avalanche diodes fabricated in the InGaAsP materials system for photon counting at near infrared wavelengths in the range from 0.9–1.6 µm. The fundamental trade-off between photon detection efficiency and dark count rate can now be managed with performance that adequately serves many applications, with low dark count rates of ∼1 kHz having been demonstrated at photon detection efficiencies of 20% for 25 µm diameter fiber-coupled devices with thermoelectric cooling. Timing jitter of less than 50 ps has been achieved, although device uniformity is shown to be essential in obtaining good jitter performance. Progress is also reported towards resolving the limitations imposed on photon counting rate by afterpulsing, with at least 50 MHz repetition frequencies demonstrated for 1 ns gated operation with afterpulsing limited to the range of 1–5%. We also present a discussion of future trends and challenges related to these devices organized according to the hierarchy of materials properties, device design concepts, signal processing and electronic circuitry, and multiplexing concepts. Whereas the materials properties of these devices may pose significant challenges for the foreseeable future, there has been considerable progress in device concepts and circuit solutions towards the present imperatives for higher counting rates and simpler device operation.

Single photon avalanche diodes (SPADs) for 1.5 μm photon counting applications

The paper reports on the design and characterization of InGaAs/InP single photon avalanche diodes (SPADs) for photon counting applications at wavelengths near 1.5 µm. It is shown how lower internal electric field amplitudes can lead to reduced dark count rates, but at the expense of degraded afterpulsing behaviour and larger timing jitter. Dark count rate behaviour provides evidence of thermally assisted tunnelling with an average thermal activation energy of ∼0.14 eV between 150 K and 220 K. Afterpulsing behaviour exhibits a structure-dependent afterpulsing activation energy, which quantifies how carrier de-trapping varies with temperature. SPAD performance simultaneously exhibits a dark count rate of 10 kHz at a detection efficiency of 20% with timing jitter of 100 ps at 200 K, and with appropriate performance tradeoffs, we demonstrate a 200 K dark count rate as low as 3 kHz, a detection efficiency as high as 45%, and a timing jitter as low as 30 ps.

InGaAsP–InP Avalanche Photodiodes for Single Photon Detection

In this paper, we describe the design, characterization, and modeling of InGaAsP/InP avalanche diodes designed for single photon detection at wavelengths of 1.55 and 1.06 mum. Through experimental and theoretical work, we investigate critical performance parameters of these single photon avalanche diodes (SPADs), including dark count rate (DCR), photon detection efficiency (PDE), and afterpulsing. The models developed for the simulation of device performance provide good agreement with experimental results for all parameters studied. For 1.55-mum SPADs, we report the relationship between DCR and PDE for gated mode operation under a variety of operating conditions. We also describe in detail the dependence of afterpulsing effects on numerous operating conditions, and in particular, we demonstrate and explain a universal functional form that describes the dependence of DCR on hold-off time at any temperature. For 1.06-mum SPADs, we present the experimentally determined relationship between DCR and detection efficiency for free-running operation, as well as simulations complementing the experimental data.

Geiger-mode avalanche photodiode focal plane arrays for three-dimensional imaging LADAR

We report on the development of focal plane arrays (FPAs) employing two-dimensional arrays of InGaAsP-based Geiger-mode avalanche photodiodes (GmAPDs). These FPAs incorporate InP/InGaAs(P) Geiger-mode avalanche photodiodes (GmAPDs) to create pixels that detect single photons at shortwave infrared wavelengths with high efficiency and low dark count rates. GmAPD arrays are hybridized to CMOS read-out integrated circuits (ROICs) that enable independent laser radar (LADAR) time-of-flight measurements for each pixel, providing three-dimensional image data at frame rates approaching 200 kHz. Microlens arrays are used to maintain high fill factor of greater than 70%. We present full-array performance maps for two different types of sensors optimized for operation at 1.06 μm and 1.55 μm, respectively. For the 1.06 μm FPAs, overall photon detection efficiency of >40% is achieved at <20 kHz dark count rates with modest cooling to ~250 K using integrated thermoelectric coolers. We also describe the first evalution of these FPAs when multi-photon pulses are incident on single pixels. The effective detection efficiency for multi-photon pulses shows excellent agreement with predictions based on Poisson statistics. We also characterize the crosstalk as a function of pulse mean photon number. Relative to the intrinsic crosstalk contribution from hot carrier luminescence that occurs during avalanche current flows resulting from single incident photons, we find a modest rise in crosstalk for multi-photon incident pulses that can be accurately explained by direct optical scattering.

InP-based Geiger-mode avalanche photodiode arrays for three-dimensional imaging at 1.06 μm

We report on the development of 32 x 32 focal plane arrays (FPAs) based on InGaAsP/InP Geiger-mode avalanche photodiodes (GmAPDs) designed for use in three-dimensional (3-D) laser radar imaging systems at 1064 nm. To our knowledge, this is the first realization of FPAs for 3-D imaging that employ a planar-passivated buried-junction InP-based GmAPD device platform. This development also included the design and fabrication of custom readout integrate circuits (ROICs) to perform avalanche detection and time-of-flight measurements on a per-pixel basis. We demonstrate photodiode arrays (PDAs) with a very narrow breakdown voltage distribution width of 0.34 V, corresponding to a breakdown voltage total variation of less than +/- 0.2%. At an excess bias voltage of 3.3 V, which provides 40% pixel-level single photon detection efficiency, we achieve average dark count rates of 2 kHz at an operating temperature of 248 K. We present the characterization of optical crosstalk induced by hot carrier luminescence during avalanche events, where we show that the worst-case crosstalk probability per pixel, which occurs for nearest neighbors, has a value of less than 1.6% and exhibits anisotropy due to isolation trench etch geometry. To demonstrate the FPA response to optical density variations, we show a simple image of a broadened optical beam.

Afterpulsing Effects in Free-Running InGaAsP Single-Photon Avalanche Diodes

We demonstrate large-area (80 mum diameter) InP-based single-photon avalanche diodes for Geiger-mode operation at 1.06 mum with dark count rates of ~1000 Hz at high detection efficiencies of 30% at 237 K, as well as simulations of dark count rate and detection efficiency that provide good agreement with measured data. Experimental results obtained using free-running operation illustrate the strong impact of afterpulsing effects for short (~200 ns) hold-off times. We present an analysis of these free-running results that quantifies the contribution of afterpulsing to the total count rate.

Geiger-mode APD camera system for single-photon 3D LADAR imaging

The unparalleled sensitivity of 3D LADAR imaging sensors based on single photon detection provides substantial benefits for imaging at long stand-off distances and minimizing laser pulse energy requirements. To obtain 3D LADAR images with single photon sensitivity, we have demonstrated focal plane arrays (FPAs) based on InGaAsP Geiger-mode avalanche photodiodes (GmAPDs) optimized for use at either 1.06 μm or 1.55 μm. These state-of-the-art FPAs exhibit excellent pixel-level performance and the capability for 100% pixel yield on a 32 x 32 format. To realize the full potential of these FPAs, we have recently developed an integrated camera system providing turnkey operation based on FPGA control. This system implementation enables the extremely high frame-rate capability of the GmAPD FPA, and frame rates in excess of 250 kHz (for 0.4 μs range gates) can be accommodated using an industry-standard CameraLink interface in full configuration. Real-time data streaming for continuous acquisition of 2 μs range gate point cloud data with 13-bit time-stamp resolution at 186 kHz frame rates has been established using multiple solid-state storage drives. Range gate durations spanning 4 ns to 10 μs provide broad operational flexibility. The camera also provides real-time signal processing in the form of multi-frame gray-scale contrast images and single-frame time-stamp histograms, and automated bias control has been implemented to maintain a constant photon detection efficiency in the presence of ambient temperature changes. A comprehensive graphical user interface has been developed to provide complete camera control using a simple serial command set, and this command set supports highly flexible end-user customization.

InP-based Negative Feedback Avalanche Diodes

The operation of InP-based single photon avalanche diodes (SPADs) in Geiger mode provides great utility for the detection of single photons at near-infrared wavelengths between 1.0 and 1.6 um. However, SPADs have performance limitations with respect to photon counting rate and the absence of photon number resolution that, at the most fundamental level, can be traced back to the positive feedback inherent in the impact ionization-driven avalanche process. In this paper, we describe the inclusion of negative feedback with best-in-class InP-based single photon avalanche diode (SPAD) structures to form negative feedback avalanche diodes (NFADs) in which many of the present limitations of SPAD operation can be overcome. The use of thin film resistors as monolithic passive negative feedback elements ensures rapid self-quenching with very low parasitic effects and wafer-level integration for creating multi-element NFAD arrays. To our knowledge, this is the first demonstration of this approach with InP-based avalanche diode structures. We present NFAD device properties, including pulse response, quenching dynamics, and photon counting performance parameters such as photon detection efficiency.

InP-Based Single-Photon Detectors and Geiger-Mode APD Arrays for Quantum Communications Applications

To meet the increasing demand from quantum communications and other photon starved applications, we have developed various InP-based single-photon detectors, including discrete single-photon avalanche diodes (SPADs), negative feedback avalanche diodes (NFADs), and Geiger-mode avalanche photodiode (GmAPD) arrays. A large quantity of InP SPADs have been fabricated. Out of 1000 devices with a 25-μm active area diameter, operated under gated mode at temperature of 233 K, with a pulse repetition rate of 1 MHz and pulse width of 1 ns, the average dark count rate and afterpulsing probability are 30 kHz and 8 × 10-5, respectively. Smaller (16-μm active area diameter) and larger (40-μm active area diameter) discrete devices have been fabricated as well, and their performances are presented along with the 25-μm diameter devices. NFAD devices can operate in free running mode and photon detection efficiency of 10-15% can be achieved without applying any hold-off time externally. When the temperature decreases from 240 to 160 K, the noise equivalent power (NEP) decreasesfrom1.9 × 10-16 to 1.8 × 10-18WHz-1/2, with the activation energy being 0.2 eV. The very low NEP at 160 K makes NFAD devices an ideal choice for long distance, entanglement-based quantum key distributions. GmAPD arrays provide an enabling technology for many active optical applications, such as 3-D laser detection and ranging (LADAR) and photon starved optical communications. Both 32 × 32 and 128 × 32 GmAPD arrays have been fabricated with high performance and good uniformity. GmAPD focal plane arrays (FPAs) with framed readout mode have enabled very high-performance flash LADAR systems. GmAPD FPAs with asynchronous readout mode will enable high rate quantum key distributions and other quantum communications applications.

Progress in self-quenching InP-based single photon detectors

The operation of InP-based single photon avalanche diodes (SPADs) in Geiger mode provides great utility for the detection of single photons at near-infrared wavelengths between 1.0 and 1.6 μm. However, SPADs have performance limitations with respect to photon counting rate and the absence of photon number resolution that, at the most fundamental level, can be traced back to the positive feedback inherent in the impact ionization-driven avalanche process. In this paper, we describe the inclusion of negative feedback with best-in-class InP-based single photon avalanche diode (SPAD) structures to form negative feedback avalanche diodes (NFADs) in which many of the present limitations of SPAD operation can be overcome. The use of thin film resistors as monolithic passive negative feedback elements ensures rapid self-quenching with very low parasitic effects. We demonstrate a qualitative difference in the performance of NFADs in the two regimes of small and large negative feedback. With small feedback, we have studied the behavior of the persistent current prior to quenching, for which we have found oscillatory behavior as well as an exponentially distributed duration. For large feedback, we find rapid quenching, accompanied by evidence for a partial discharge of the detector capacitance, leading to charge flows as low as ~3 ×105 carriers associated with each avalanche event.