Dualband Quantum Well Infrared Photodetector Focal Plane Arrays Research Articles

High speed QWIP FPAs on InP substrates

Quantum well infrared photodetector (QWIP) technology has allowed the realization of low cost staring focal plane arrays (FPAs). However, AlGaAs/(In)GaAs QWIP FPAs suffer from low quantum and conversion efficiencies under high frame rate and/or low background conditions. We extensively discuss the effect of sensor gain on the FPA performance under various operating conditions, and highlight the superiority of the InP/InGaAs material system with respect to AlGaAs/GaAs for high speed/low background thermal imaging applications. InP/InGaAs QWIPs, providing a bias adjustable gain in a wide range, offer the flexibility of adapting the FPA to strict operating conditions. We also present an experimental comparison of large format AlGaAs/GaAs and (strained) InP/InGaAs QWIP FPAs under different operating conditions. A 640 × 512 QWIP FPA constructed with the 40-well strained InP/In 0.48Ga 0.52As material system displays a cut-off wavelength of 9.7 μm ( λ p = 8.9 μm) with a BLIP temperature higher than 65 K ( f/2), and a peak quantum efficiency as high as 12% with a broad spectral response (Δ λ/ λ p = 17%). The conversion efficiency of the FPA pixels is as high as 20% under large bias (4 V) where the detectivity is reasonably high (∼3 × 10 10 cm Hz 1/2/W, f/2, 65 K). While providing a considerably higher quantum efficiency than the pixels of a similar AlGaAs/GaAs FPA, the InP/InGaAs QWIP provides similar NETD values with much shorter integration times and, being less sensitive to the read noise, successfully operates with sub-millisecond integration times. The results clearly demonstrate that InP based material systems display high potential for single- and dual-band QWIP FPAs by overcoming the limitations of the standard GaAs based QWIPs under high frame rate and/or low background conditions.

Large format voltage tunable dual-band QWIP FPAs

Third generation thermal imagers with dual/multi-band operation capability are the prominent focus of the current research in the field of infrared detection. Dual band quantum-well infrared photodetector (QWIP) focal plane arrays (FPAs) based on various detection and fabrication approaches have been reported. One of these approaches is the three-contact design allowing simultaneous integration of the signals in both bands. However, this approach requires three In bumps on each pixel leading to a complicated fabrication process and lower fill factor. If the spectral response of a two-stack QWIP structure can effectively be shifted between two spectral bands with the applied bias, dual band sensors can be implemented with the conventional FPA fabrication process requiring only one In bump on each pixel making it possible to fabricate large format dual band FPAs at the cost and yield of single band detectors. While some disadvantages of this technique have been discussed in the literature, the detailed assessment of this approach has not been performed at the FPA level yet. We report the characteristics of a large format (640 × 512) voltage tunable dual-band QWIP FPA constructed through series connection of MWIR AlGaAs–InGaAs and LWIR AlGaAs–GaAs multi-quantum well stacks, and provide a detailed assessment of the potential of this approach at both pixel and FPA levels. The dual band FPA having MWIR and LWIR cut-off wavelengths of 5.1 and 8.9 μm provided noise equivalent temperature differences as low as 14 and 31 mK ( f/1.5) with switching voltages within the limits applicable by commercial read-out integrated circuits. The results demonstrate the promise of the approach for achieving large format low cost dual band FPAs.

Quantum Well and Quantum Dot Based Detector Arrays for Infrared Imaging

ABSTRACTA mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 320x256 pixel quantum well infrared photodetector (QWIP) dualband focal plane arrays (FPAs) have been demonstrated with excellent imagery. Currently, we are developing a 1024x1024 pixel simultaneous pixel co-registered dualband QWIP FPA. In addition, epitaxially grown self-assembled InAs/InGaAs/GaAs quantum dots (QDs) are exploited for the development of large-format FPAs. The Dot-in-a-Well (DWELL) structures were experimentally shown to absorb both 45° and normal incident light, therefore a reflection grating structure was used to enhance the quantum efficiency. The devices exhibit peak responsivity out to 8.1 microns, with peak detectivity reaching ∼ 1 × 1010 Jones at 77 K. The devices were fabricated into the first LWIR 640x512 pixel QDIP FPA, which has produced excellent infrared imagery with NETD of 40 mK at 60K operating temperature.

Towards dualband megapixel QWIP focal plane arrays

Mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) 1024×1024 pixel quantum well infrared photodetector (QWIP) focal planes have been demonstrated with excellent imaging performance. The MWIR QWIP detector array has demonstrated a noise equivalent differential temperature (NEΔT) of 17mK at a 95K operating temperature with f/2.5 optics at 300K background and the LWIR detector array has demonstrated a NEΔT of 13mK at a 70K operating temperature with the same optical and background conditions as the MWIR detector array after the subtraction of system noise. Both MWIR and LWIR focal planes have shown background limited performance (BLIP) at 90K and 70K operating temperatures respectively, with similar optical and background conditions. In addition, we have demonstrated MWIR and LWIR pixel co-registered simultaneously readable dualband QWIP focal plane arrays. In this paper, we will discuss the performance in terms of quantum efficiency, NEΔT, uniformity, operability, and modulation transfer functions of the 1024×1024 pixel arrays and the progress of dualband QWIP focal plane array development work.

Laboratory and field imaging test results on single-color and dual-band QWIP focal plane arrays

We report on recent laboratory and field measurements on quantum well infrared photodetector (QWIP) focal plane arrays (FPAs). The results of laboratory measurements of imaging performance such as noise-equivalent temperature difference (NE ΔT), minimum resolvable temperature, conversion efficiency, uniformity of response and dark current and their dependence on operating temperature are presented on large format (640×480 pixels) single-color long-wavelength infrared (LWIR) and dual-band (256×256 pixels) mid-wavelength infrared (MWIR)/LWIR arrays. We found that under optimum operating conditions (65 K and 1 V bias), the NE ΔT of the LWIR FPA was approximately 30 mK and was limited by the optics and noise from the closed-cycle cooler. We will show field imagery of military targets taken with this FPA. In addition, field imagery taken with the LWIR QWIP camera of a large-transient event will be compared with that taken with an InSb MWIR camera. We will also show imagery of a recent total eclipse of the moon. We will also present laboratory results on a simultaneously integrating, pixel-registered dual-band FPA showing excellent operability and response uniformity with NE ΔT of approximately 30 mK in both bands ( T=60 K). The dual-band FPA was also taken to the field and we will present imagery of various targets acquired with this FPA.

640×486 long-wavelength two-color GaAs/AlGaAs quantum well infrared photodetector (QWIP) focal plane array camera

We have designed and fabricated an optimized long-wavelength/very-long wavelength two-color quantum well infrared photodetector (QWIP) device structure. The device structure was grown on a 3-in semi-insulating GaAs substrate by molecular beam epitaxy (MBE). The wafer was processed into several 640/spl times/486 format monolithically integrated 8-9 and 14-15 /spl mu/m two-color (or dual wavelength) QWIP focal plane arrays (FPAs). These FPAs were then hybridized to 640/spl times/486 silicon CMOS readout multiplexers. A thinned (i.e., substrate removed) FPA hybrid was integrated into a liquid helium cooled dewar for electrical and optical characterization and to demonstrate simultaneous two-color imagery. The 8-9 /spl mu/m detectors in the FPA have shown background limited performance (BLIP) at 70 K operating temperature for 300 K background with f/2 cold stop. The 14-15 /spl mu/m detectors of the FPA reaches BLIP at 40 K operating temperature under the same background conditions. In this paper we discuss the performance of this long-wavelength dualband QWIP FPA in terms of quantum efficiency, detectivity, noise equivalent temperature difference (NE/spl Delta/T), uniformity, and operability.