Bora M. Onat

SWIR/MWIR InP-Based p-i-n Photodiodes With InGaAs/GaAsSb Type-II Quantum Wells

This paper presents the performance characteristics of InP-based p-i-n photodiodes with strain-compensated and lattice-matched InGaAs/GaAsSb type-II multiple quantum well (MQW) absorption regions. The results show that photodiodes with strain-compensated and lattice-matched absorption regions have optical response out to 3.4 and 2.8 μm with dark current densities of 9.7 and 1.66 mA cm-2,respectively, at 290 K under -0.5 V reverse bias. The carrier transport mechanism responsible for the difference in responsivity and detectivity between strain-compensated and lattice-matched InGaAs/GaAsSb MQWs is discussed.

Characterization of an InGaAs/InP-based single-photon avalanche diode with gated-passive quenching with active reset circuit

An improved gated-mode passive quenching with active reset (gated-PQAR) circuit is utilized in conjunction with an InGaAs/InP single-photon avalanche photodiode (SPAD). Photon detection efficiency (PDE) and dark count probability (DCP) were measured at a gate repetition rate of 1 MHz. The reduced afterpulsing afforded by the gated-PQAR circuit enabled measurement of afterpulsing for hold-off times as short as 10 ns. The timing resolution (jitter) for different excess biases has also been investigated. At 230 K and an excess bias of 2.5 V, 0.3% afterpulse probability for a 10 ns hold-off time was achieved with 13% PDE, 2 × 10−6 DCP, 160 ps jitter, and 0.2 ns effective gate width. For the same hold-off time, at a higher excess bias of 3.5 V, 30% PDE, 1 × 10−5 DCP and 120 ps jitter were achieved with 7% afterpulse probability with an effective gate width of 0.7 ns.

Demonstration of a Room-Temperature InP-Based Photodetector Operating Beyond 3

An InP-based p-i-n photodiode with optical response out to 3.4 μm was designed and grown by molecular beam epitaxy (MBE). One hundred pairs of 7-nm In_0.34Ga_0.66As/5-nm GaAs_0.25Sb_0.75 quantum wells strain compensated to InP were used as the absorption region. The device showed a dark current density of 9.6 mA/cm² under -0.5-V reverse bias, a responsivity of 0.03 A/W, and a detectivity of 2.0 × 10⁸ cm·Hz^1/2·W^-1 at 3 μm at 290 K.

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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.

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We present a new and innovative short-wave infrared (SWIR) hyperspectral imaging focal plane array (FPA) concept for bulk and trace standoff explosives detection. The proposed technology combines conventional uncooled InGaAs based SWIR imaging with the wavelength selectivity of a monolithically integrated solid-state Fabry-Perot interferometer. Each pixel of the array consists of a group of sub-pixels in which each sub-pixel is tuned to absorb a separate wavelength. The relative responses from the sub-pixels (i.e. wavelengths) are compared to the spectral characteristics of explosives in the SWIR to detect and locate them within an imaged scene among various background materials. The novel technology will be compact, and consume low power such that it can be used as a handheld device or mounted for persistent surveillance of crowded areas and checkpoints. The technology does not use any scanning nor tuning apparatuses such as MEMS devices, and is therefore fast, compact, lightweight and not susceptible to vibration. The technology is therefore ideal for man portable applications and unmanned vehicle platforms. An eyesafe (covert) illuminator may be used to provide illumination in situations when ambient light conditions are not sufficient. We will present a detailed design of the novel focal plane array and a theoretical standoff distance and false rates study.

Progress in self-quenching InP-based single photon detectors

The goal of this study is to present a systematic approach to reduce dark current in InGaAs based SWIR imaging arrays. We achieved a factor of 10 reduction of dark current compared to our standard processing with improved uniformity and a factor of ~2.5 reduction than previous state of the art.

A solid-state hyperspectral imager for real-time standoff explosives detection using shortwave infrared imaging

Different type-II InGaAs/GaAsSb quantum well design structures on InP substrate for mid-infrared emission has been modeled by six band k•p method. The dispersion relations, optical matrix element, optical gain and spontaneous emission rate are calculated. The effects of the parameters of quantum wells (thickness, composition) and properties of cladding layers were investigated. For injected carrier concentration of 5×1012 cm-2, peak gain values around 2.6-2.7 μm wavelengths of the order of 1000 cm-1 can be achieved, which shows that type-II InGaAs/GaAsSb quantum wells are suitable for infrared laser operation beyond 2μm at room temperature.

A systematic approach to dark current reduction in InGaAs-based photodiode arrays for shortwave infrared imaging

We report reduced afterpulsing for a high-performance InGaAs/InP single photon avalanche photodiode (SPAD) using a gated-mode passive quenching with active reset (gated-PQAR) circuit. Photon detection efficiency (PDE) and dark count probability (DCP) were measured at a gate repetition rate of 1 MHz. With a double-pulse measurement technique, the afterpulsing probability was measured for various hold-off times. At 230K, 0.3% afterpulsing probability for a 10 ns hold-off time was achieved with 13% PDE, 2×10-6 DCP and 0.4 ns effective gate width. For the same hold off time, 30% PDE and 1×10-5 DCP was achieved with 6% afterpulsing probability for an effective gate width of 0.7 ns.

Modeling of the type-II InGaAs/GaAsSb quantum well designs for mid-infrared laser diodes by k•p method

Operational characteristics of InGaAs/InAlAs based MQW modulators, with different device designs, for a wide temperature range (-40/spl deg/C to 70/spl deg/C) are reported. The modulator peak extinction ratio wavelength is shown to be a linear function of temperature.