Edward M. Luong

10–16 μm Broadband quantum well infrared photodetector

A very long wavelength broadband infrared detector, sensitive over a 10–16 μm spectral range, based on GaAs/AlxGa1−xAs quantum wells grown by molecular beam epitaxy, has been demonstrated. Wavelength broadening of Δλ/λp∼42% is observed to be about a 400% increase compared to a typical bound-to-quasibound quantum well infrared photodetector (QWIP). In this device structure, which is different from typical QWIP device structures, two different gain mechanisms associated with photocurrent electrons and dark current electrons were observed and explained. Even with broader response, D*∼1×1010 cmHz/W at T=55 K is comparable to regular QWIPs with similar cutoff wavelengths.

Long-wavelength 256/spl times/256 GaAs/AlGaAs quantum well infrared photodetector (QWIP) palm-size camera

A 9 /spl mu/m cutoff 256/spl times/256 palm-size quantum well infrared photodetector (QWIP) camera weighing only 2.5 lbs, and using 5.5 W of power has been demonstrated. Excellent imagery, with a noise equivalent differential temperature (NE/spl Delta/T) of 23 mK has been achieved. It is well known that QWIP has very low 1/f noise, high operability, and uniformity. As a result, this camera uses a prerecorded nonuniformity correction table (i.e., gains and offsets) stored in its read-only-memory during operation, which enabled the miniaturization of this camera. In this paper, we discuss the development of this very sensitive long-wavelength infrared (LWIR) camera based on a GaAs/AlGaAs QWIP focal plane array (FPA) and its performance in terms of quantum efficiency, NE/spl Delta/T, MRDT, uniformity, and operability.

Development of quantum well, quantum dot, and type II superlattice infrared photodetectors

Abstract We present an overview of III-V semiconductor-based infrared detector and focal plane array development at the NASA Jet Propulsion Laboratory in recent years. Topics discussed include: (1) the development of long-wavelength quantum well infrared photodetector for imaging spectrometer applications, (2) the concept and realization of the submonolayer quantum dot infrared photodetector (SML-QDIP) as an alternative to the standard QDIP-based on Stranski-Krastanov (SK) quantum dots, (3) the mid-wavelength infrared quantum dot barrier infrared detector with extended cutoff wavelength, and (4) high-performance type-II superlattice long-wavelength infrared detectors based on the complementary barrier infrared detector architecture.

Recent developments and applications of quantum well infrared photodetector focal plane arrays

Abstract One of the simplest device realizations of the classic particle-in-the-box problem of basic quantum mechanics is the quantum well infrared photodetector (QWIP). In this paper we discuss the optimization of the detector design, material growth and processing that has culminated in realization of large format long-wavelength QWIP cameras, holding forth great promise for many applications in 6–25 μm wavelength range in science, medicine, defense and industry. In addition, we present the recent developments in long-wavelength/very long-wavelength dualband QWIP imaging camera for various applications.

High operating temperature nBn detector with monolithically integrated microlens

We demonstrate an InAsSb nBn detector monolithically integrated with a microlens fabricated on the back side of the detector. The increase in the optical collection area of the detector resulted in a five-fold enhancement of the responsivity to Rp = 5.5 A/W. The responsivity increases further to Rp = 8.5 A/W with an antireflection coating. These 4.5 μm cut-off wavelength antireflection coated detectors with microlenses exhibited a detectivity of D* (λ) = 2.7 × 1010 cmHz0.5/W at T = 250 K, which can be reached easily with a single-stage thermoelectric cooler or with a passive radiator in the space environment. This represents a 25 K increase in the operating temperature of these devices compared to the uncoated detectors without an integrated microlens.

Mid-wavelength high operating temperature barrier infrared detector and focal plane array

We analyze and compare different aspects of InAs/InAsSb and InAs/GaSb type-II superlattices for infrared detector applications and argue that the former is the most effective when implemented for mid-wavelength infrared detectors. We then report results on an InAs/InAsSb superlattice based mid-wavelength high operating temperature barrier infrared detector. At 150 K, the 50% cutoff wavelength is 5.37 μm, the quantum efficiency at 4.5 μm is ∼52% without anti-reflection coating, the dark current density under −0.2 V bias is 4.5 × 10−5 A/cm2, and the dark-current-limited and the f/2 black-body (300 K background in 3–5 μm band) specific detectivities are 4.6 × 1011 and 3.0 × 1011 cm-Hz1/2/W, respectively. A focal plane array made from the same material exhibits a mean noise equivalent differential temperature of 18.7 mK at 160 K operating temperature with an f/2 optics and a 300 K background, demonstrating significantly higher operating temperature than InSb.

Monolithically integrated carbon nanotube bundle field emitters using a double-SOI process

Carbon nanotube (CNT) field emitters offer high energy efficiency and high current density needed for miniature analytical instruments for space exploration. This paper reports design and fabrication of monolithically gate-integrated carbon nanotube bundle field electron emitters using double silicon-on-insulator (SOI) substrates. While gate integration with CNT field emitters has been reported before, this process and its extension (as in manylayered- SOI substrates) allow monolithic integration of multiple electrodes for electron beam shaping to produce a highly compact field emission electron gun. In addition, this process offers improved dimensional precision, and can be used to integrate gates with single CNT bundle or with an array as needed for an application.

Quantum Well Infrared Photodetectors: Device Physics and Light Coupling

It is customary to make infrared (IR) detectors in the long wavelength range (8 – 20 urn) by utilizing the interband transition which promotes an electron across the bandgap (Eg) from the valence band to the conduction. These photo-electrons can be collected efficiently, thereby producing a photocurrent in the external circuit. Since the incoming photon has to promote an electron from the valence band to the conduction band, the energy of the photon (hv) must be higher than the Eg of the photosensitive material. Therefore, the spectral response of the detectors can be controlled by manipulating Eg of the photosensitive material. Detection of very long wavelength IR radiation up to 20 μm requires small bandgaps down to 62 meV. Examples of such materials meeting these requirements are Hg1-xCdxTe and Pb1-xSnxTe in which the energy gap can be controlled by varying x. It is well known that these low bandgap materials are more difficult to grow and process than large bandgap semiconductors such as GaAs. These difficulties motivate the exploration of utilizing the intersubband transitions in multi quantum well (MQW) structures made of large bandgap semiconductors.