Low-frequency noise has been studied in a mid-wavelength infrared InAs/GaSb type-II superlattice-based focal plane array. Low-frequency noise is observed under reverse bias but not at zero bias, even in the presence of photo-current. The magnitude of low-frequency noise was separately measured as a function of operating temperature and operation bias. The low-frequency noise is linearly correlated with the generation-recombination component of the dark current. No correlation of low-frequency noise with photo-current or diffusion dark current was found.
We report a bias selectable dual-band Type-II superlattice-based short-wave infrared (SWIR) and mid-wave infrared (MWIR) co-located photodetector capable of active and passive imaging. A new double-layer etch-stop scheme is introduced for back-side-illuminated photodetectors, which enhanced the external quantum efficiency both in the SWIR and MWIR spectral regions. Temperature-dependent dark current measurements of pixel-sized 27 μm detectors found the dark current density to be ~1×10-5 A/cm2 for the ∼4.2 μm cut-off MWIR channel at 140 K. This corresponded to a reasonable imager noise equivalent difference in temperature of ∼49 mK using F⁄2.3 optics and a 10 ms integration time (tint), which lowered to ∼13 mK at 110 K using and integration time of 30 ms, illustrating the potential for high-temperature operation. The SWIR channel was found to be limited by readout noise below 150 K. An excellent imagery from the dual-band imager exemplifying pixel coincidence is shown.
We report a bias selectable dual-band mid-wave infrared (MWIR) and long-wave infrared (LWIR) co-located detector with 3 μm active region thickness per channel that is highly selective and can perform under high operating temperatures for the MWIR band. Under back-side illumination, a temperature evolution study of the MWIR detector’s electro-optical performance found the 300 K background-limit with 2π field-of-view to be achieved below operating temperatures of 160 K, at which the temperature’s 50% cutoff wavelength was 5.2 μm. The measured current reached the system limit of 0.1 pA at 110 K for 30 μm pixel-sized diodes. At 77 K, where the LWIR channel operated with a 50% cutoff wavelength at 11.2 μm, an LWIR selectivity of ∼17% was achieved in the MWIR wave band between 3 and 4.7 μm, making the detector highly selective.
Active and passive imaging in a single camera based on the combination of short-wavelength and mid-wavelength
infrared detection is highly needed in a number of tracking and reconnaissance missions. Due to its versatility in
band-gap engineering, Type-II InAs/GaSb/AlSb superlattice has emerged as a candidate highly suitable for this
multi-spectral detection.
In this paper, we report the demonstration of high performance bias-selectable dual-band short-/mid-wavelength
infrared photodetectors based on InAs/GaSb/AlSb type-II superlattice with designed cut-off wavelengths of 2 μm
and 4 μm. Taking advantages of the high performance short-wavelength and mid-wavelength single color
photodetectors, back-to-back p-i-n-n-i-p photodiode structures were grown on GaSb substrate by molecular beam
epitaxy. At 150 K, the short-wave channel exhibited a quantum efficiency of 55%, a dark current density of 1.0x10-9 A/cm2 at -50 mV bias voltage, providing an associated shot noise detectivity of 3.0x1013 Jones. The mid-wavelength
channel exhibited a quantum efficiency of 33% and a dark current density of 2.6x10-5 A/cm2 at 300 mV bias voltage,
resulting in a detectivity of 4.0x1011 Jones. The operations of the two absorber channels are selectable by changing
the polarity of applied bias voltage.
Recently, the type-II InAs/GaSb superlattice (T2SL) material platform is considered as a potential alternative for
HgCdTe technology in long wavelength infrared (LWIR) imaging. This is due to the incredible growth in the
understanding of its material properties and improvement of device processing which leads to design and fabrication of
better devices. In this paper, we report electrical low frequency noise measurement on a high performance type-II
InAs/GaSb superlattice 1024×1024 LWIR focal plane array.
One of the biggest challenges of improving the electrical performance in Type II InAs/GaSb superlattice
photodetector is suppressing the surface leakage. Surface leakage screens important bulk dark current mechanisms,
and brings difficulty and uncertainty to the material optimization and bulk intrinsic parameters extraction such as
carrier lifetime and mobility. Most of surface treatments were attempted beyond the mid-infrared (MWIR) regime
because compared to the bulk performance, surface leakage in MWIR was generally considered to be a minor factor.
In this work, we show that below 150K, surface leakage still strongly affects the electrical performance of the very
high bulk performance p-π-M-n MWIR photon detectors. With gating technique, we can effectively eliminate the
surface leakage in a controllable manner. At 110K, the dark current density of a 4.7 μm cut-off gated photon diode is
more than 2 orders of magnitude lower than the current density in SiO2 passivated ungated diode. With a quantum
efficiency of 48%, the specific detecivity of gated diodes attains 2.5 x 1014 cmHz1/2/W, which is 3.6 times higher than
that of ungated diodes.
Recent efforts have been paid to elevate the operating temperature of Type II superlattice Mid Infrared
photon detectors. Using M-structure superlattice, novel device architectures have been developed, resulting
in significant improvement of the device performances. In this paper, we will compare different
photodetector architectures and discuss the optimization scheme which leads to almost one order of
magnitude of improvement to the electrical performance. At 150K, single element detectors exhibit a
quantum efficiency above 50%, and a specific detectivity of 1.05x1012 cm.Hz1/2/W. BLIP operation with a
300K background and 2π FOV can be reached with an operating temperature up to 180K. High quality focal
plane arrays were demonstrated with a noise equivalent temperature difference (NEDT) of 11mK up to
120K. Human body imaging is achieved at 150K with NEDT of 150mK.
Infrared detection technologies entering the third generation demand performances for higher
detectivity, higher operating temperature, higher resolution and multi-color detection, all accomplished with
better yield and lower manufacturing/operating costs. Type-II antimonide based superlattices (T2SL) are
making firm steps toward the new era of focal plane array imaging as witnessed in the unique advantages and
significant progress achieved in recent years. In this talk, we will present the four research themes towards
third generation imagers based on T2SL at the Center for Quantum Devices. High performance LWIR
megapixel focal plane arrays (FPAs) are demonstrated at 80K with an NEDT of 23.6mK using f/2 optics, an
integration time of 0.13ms and a 300K background. MWIR and LWIR FPAs on non-native GaAs substrates
are demonstrated as a proof of concept for the cost reduction and mass production of this technology. In the
MWIR regime, progress has been made to elevate the operating temperature of the device, in order to avoid
the burden of liquid nitrogen cooling. We have demonstrated a quantum efficiency above 50%, and a
specific detectivity of 1.05x1012 cm.Hz1/2/W at 150K for 4.2μm cut-off single element devices. Progress on
LWIR/LWIR dual color FPAs as well as novel approaches for FPA fabrication will also be discussed.
One of the great advantages of Type II InAs/GaSb superlattice over other competing technologies for
the third generation infrared imagers is the potential to have excellent uniformity across a large area as
the electronic structure of the material is controlled by the layer thicknesses, not by the composition of
the materials. This can economize the material growth, reduce the fabrication cost, and especially
allow the realization of large format imagers.
In this talk, we report the molecular beam epitaxial growth of Type II superlattices on a 3" GaSb
substrate for long wavelength infrared detection. The material exhibits excellent structural, optical and
electrical uniformity via AFM, Xray, quantum efficiency and I-V measurements. At 77K, 11μm cutoff
photodiodes exhibit more than 45% quantum efficiency, and a dark current density of 1.0x10-4A/cm2 at 50 mV, resulting in a specific detectivity of 6x1011 cm.Hz1/2/W.
Recent efforts have been paid to elevate the operating temperature of Type II InAs/GaSb superlattice
Mid Infrared photon detectors. Optimized growth parameters and interface engineering technique
enable high quality material with a quantum efficiency above 50%. Intensive study on device
architecture and doping profile has resulted in almost one order of magnitude of improvement to the
electrical performance and lifted up the 300K-background BLIP operation temperature to 166K. At
77K, the ~4.2 μm cut-off devices exhibit a differential resistance area product in excess of the
measurement system limit (106 Ohm.cm2) and a detectivity of 3x1013cm.Hz1/2/W. High quality focal
plane arrays were demonstrated with a noise equivalent temperature of 10mK at 77K. Uncooled
camera is capable to capture hot objects such as soldering iron.
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