Axel Reisinger

Mid-IR focal plane array based on type-II InAs/GaSb strain layer superlattice detector with nBn design

A midwave infrared camera (λc=4.2μm) with a 320×256 focal plane array (FPA) based on type-II InAs∕GaSb strain layer superlattice (SLs) has been demonstrated. The detectors consist of an nBn heterostructure, wherein the SL absorber and contact layers are separated by a Al0.2Ga0.8Sb barrier layer, which is designed to have a minimum valence band offset. Unlike a PN junction, the size of the device is not defined by a mesa etch but confined by the lateral diffusion length of minority carriers. At 77K, the FPA demonstrates a temporal noise equivalent temperature difference (NETD) of 23.8mK (Tint=16.3ms and Vb=0.7V) with a peak quantum efficiency and detectivity at 3.8μm equal to 52% and 6.7×1011 Jones, respectively.

Single bump, two-color quantum dot camera

The authors report a two-color, colocated quantum dot based imaging system used to take multicolor images using a single focal plane array (FPA). The dots-in-a-well (DWELL) detectors consist of an active region composed of InAs quantum dots embedded in In.15Ga.85As quantum wells. DWELL samples were grown using molecular beam epitaxy and fabricated into 320×256 focal plane arrays with indium bumps. The FPA was then hybridized to an Indigo ISC9705 readout circuit and tested. Calibrated blackbody measurements at a device temperature of 77K yield midwave infrared and long wave infrared noise equivalent difference in temperature of ∼55 and 70mK.

Comparison of Quantum Dots-in-a-Double-Well and Quantum Dots-in-a-Well Focal Plane Arrays in the Long-Wave Infrared

Our previous research has reported on the development of the first generation of quantum dots-in-a-well (DWELL) focal plane arrays (FPAs), which are based on InAs quantum dots (QDs) embedded in an InGaAs well having GaAs barriers, which have demonstrated spectral tunability via an externally applied bias voltage. More recently, technologies in DWELL devices have been further advanced by embedding InAs QDs in InGaAs and GaAs double wells with AlGaAs barriers, leading to a less strained InAs/InGaAs/GaAs/AlGaAs heterostructure. These lower strain quantum dots-in-a-double-well devices exhibit lower dark current than the previous generation DWELL devices while still demonstrating spectral tunability. This paper compares two different configurations of double DWELL (DDWELL) FPAs to a previous generation DWELL detector and to a commercially available quantum well infrared photodetector (QWIP). All four devices are 320 × 256 pixel FPAs that have been fabricated and hybridized with an Indigo 9705 read-out integrated circuit. Radiometric characterization, average array responsivity, array uniformity and measured noise equivalent temperature difference for all four devices is computed and compared at 60 K. Overall, the DDWELL devices had lower noise equivalent temperature difference and higher uniformity than the first-generation DWELL devices, although the commercially available QWIP has demonstrated the best performance.

Comparison of Long-Wave Infrared Quantum-Dots-in-a-Well and Quantum-Well Focal Plane Arrays

This paper reports on a comparison between a commercially available quantum-well infrared focal plane array (FPA) and a custom quantum-dot (QD)-in-a-well (DWELL) infrared FPA in the long-wave infrared (LWIR). The DWELL detectors consist of an active region composed of InAs QDs embedded in In0.15Ga0.85As quantum wells. DWELL samples were grown using molecular beam epitaxy and fabricated into 320 times 256 pixels FPA with a flip-chip indium bump technique. Both the DWELL and QmagiQ commercial quantum-well detector were hybridized to an Indigo ISC9705 readout circuit and tested in the same camera system. Calibrated blackbody measurements at a device temperature of 60 K with LWIR optics yield a noise equivalent change in temperature of 17 mK and 91 mK for quantum-well and DWELL FPAs operating at 0.95- and 0.58-V biases, respectively. The comparison of the DWELL and quantum-well FPA when imaging a 35degC black body showed that the DWELL had a signal-to-noise ratio of 124 while the quantum-well FPA showed 1961. As well, the quantum-well FPA showed a higher collection efficiency of 1.3 compared to the DWELL.

A voltage-tunable multispectral 320 × 256 InAs/GaAs quantum-dot infrared focal plane array

A voltage-tunable multispectral 320 × 256 infrared imaging focal plane array (FPA) is reported. It is based on InAs/GaAs quantum dots infrared phototdetctors (QDIP) with GaAs and In0.20Ga0.80As capping layers, corresponding to the extended middle-wave infrared (5–8 µm) and long-wave infrared (8–12 µm) detection bands, respectively. The FPA shows a noise-equivalent temperature difference of 172 mK at an operating temperature of 67 K. Voltage-tunable multispectral imaging was also achieved. Since each of the detection spectra of the QD FPA can be individually tuned by engineering its QD capping layer, this approach offers great flexibility in designing of a multispectral FPA.

1024 x 1024 LWIR SLS FPAs: status and characterization

An infrared sensor technology that has made quick progress in recent years is the photodiode based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). We have developed Focal Plane Arrays (FPAs) with up to a million pixels, quantum efficiency exceeding 50%, and cutoff wavelength ~ 10 microns. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point of midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current state-of-the-art of this sensor technology at this critical stage of its evolution.

Two-color quantum well infrared photodetector focal plane arrays

QmagiQ LLC, has recently completed building and testing high operability two-color Quantum Well Infrared Photodetector (QWIP) focal plane arrays (FPAs). The 320 x 256 format dual-band FPAs feature 40-micron pixels of spatially registered QWIP detectors based on III-V materials. The vertically stacked detectors in this specific midwave/longwave (MW/LW) design are tuned to absorb in the respective 4-5 and 8-9 micron spectral ranges. The ISC0006 Readout Integrated Circuit (ROIC) developed by FLIR Systems Inc. and used in these FPAs features direct injection (DI) input circuitry for high charge storage with each unit cell containing dual integration capacitors, allowing simultaneous scene sampling and readout for the two distinct wavelength bands. Initial FPAs feature pixel operabilities better than 99%. Focal plane array test results and sample images will be presented.

Absolute temperature measurements using a two-color QWIP focal plane array

The infrared photon flux emitted by an object depends not only on its temperature but also on a proportionality factor referred to as its emissivity. Since the latter parameter is usually not known quantitatively a priori, any temperature determination based on single-band radiometric measurements suffers from an inherent uncertainty. Recording photon fluxes in two separate spectral bands can in principle circumvent this limitation. The technique amounts to solving a system of two equations in two unknowns, namely, temperature and emissivity. The temperature derived in this manner can be considered absolute in the sense that it is independent of the emissivity, as long as that emissivity is the same in both bands. QmagiQ has previously developed a 320x256 midwave/longwave staring focal plane array which has been packaged into a dual-band laboratory camera. The camera in question constitutes a natural tool to generate simultaneous and independent emissivity maps and temperature maps of entire two-dimensional scenes, rather than at a single point on an object of interest. We describe a series of measurements we have performed on a variety of targets of different emissivities and temperatures. We examine various factors that affect the accuracy of the technique. They include the influence of the ambient radiation reflected off the target, which must be properly accounted for and subtracted from the collected signal in order to lead to the true target temperature. We also quantify the consequences of spectrally varying emissivities.

Infrared imaging with quantum wells and strained layer superlattices

In the last few years infrared focal plane arrays based on Type-I GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) have been commercialized, providing excellent cost-effective imaging for security and surveillance and gas imaging applications. A second cooled infrared sensor technology that has made significant advances in recent years is photodiodes based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). Imaging chips with upto a million pixels, quantum efficiency exceeding 50%, and cutoff wavelength exceeding 10 microns have been recently demonstrated. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point of QWIP and midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current state-of-the-art of both these sensor technologies at this critical stage of their evolution.

Demonstration of a two-color 320 x 256 quantum dots-in-a-well focal plane array

We report the first successful demonstration of a two color, co-located infrared focal plane array based on novel InAs/InGaAs quantum dots-in-a-well photodetectors. Two distinct responses (¿1~4.5um and ¿2~8.5um) were observed under 300K f2 irradiance.