Recent efforts to improve the performance of Type II InAs/GaSb superlattice photodiodes and focal
plane arrays (FPA) have been reviewed. The theoretical bandstructure models have been discussed
first. A review of recent developments in growth and characterization techniques is given. The efforts
to improve the performance of LWIR photodiodes and the latest result have been reported. The results
of both small and large format LWIR FPAs, the latest results to elevate the operating temperature of
MWIR photodiodes and FPAs, the latest results of two color FPAs, the results of novel minority
unipolar devices (pMp) and finally the results of photodiode and FPA fabrication on GaAs substrates
are reviewed.
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.
In recent years, the type-II superlattice (T2SL) material platform has seen incredible growth in
the understanding of its material properties which has lead to unprecedented development in the arena
of device design. Its versatility in band-structure engineering is perhaps one of the greatest hallmarks
of the T2SL that other material platforms are lacking. In this paper, we discuss advantages of the
T2SL, specifically the M-structure T2SL, which incorporates AlSb in the traditional InAs/GaSb
superlattice. Using the M-structure, we present a new unipolar minority electron detector coined as
the P-M-P, the letters which describe the composition of the device. Demonstration of this device
structure with a 14μm cutoff attained a detectivity of 4x1010 Jones (-50mV) at 77K. As device
performance improves year after year with novel design contributions from the many researchers in
this field, the natural progression in further enabling the ubiquitous use of this technology is to reduce
cost and support the fabrication of large infrared imagers. In this paper, we also discuss the use of
GaAs substrates as an enabling technology for third generation imaging on T2SLs. Despite the 7.8%
lattice mismatch between the native GaSb and alternative GaAs substrates, T2SL photodiodes grown
on GaAs at the MWIR and LWIR have been demonstrated at an operating temperature of 77K.
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.
The bandstructure tunability of Type II antimonide-based superlattices has been significantly enhanced since the
introduction of the M-structure superlattice, resulting in significant improvements of Type II superlattice infrared
detectors. By using M-structure, we developed the pMp design, a novel infrared photodetector architecture that
inherits the advantages of traditional photoconductive and photovoltaic devices. This minority electron unipolar
device consists of an M-structure barrier layer blocking the transport of majority holes in a p-type
semiconductor, resulting in an electrical transport due to minority carriers with low current density. Applied for
the very long wavelength detection, at 77K, a 14μm cutoff detector exhibits a dark current 3.3 mA/cm2, a
photoresponsivity of 1.4 A/W at 50mV bias and the associated shot-noise detectivity of 4x1010 Jones.
Type-II InAs/GaSb Superlattice (SL), a system of multi interacting quantum wells was first
introduced by Nobel Laureate L. Esaki in the 1970s. Since then, this low dimensional system has
drawn a lot of attention for its attractive quantum mechanics properties and its grand potential for the
emergence into the application world, especially in infrared detection. In recent years, Type-II
InAs/GaSb superlattice photo-detectors have experienced significant improvements in material
quality, structural designs and imaging applications which elevated the performances of Type-II
InAs/GaSb superlattice photodetectors to a comparable level to the state-of-the-art Mercury Cadmium
Telluride. We will present in this talk the current status of the state-of-the-art Type II superlattice
photodetectors and focal plane arrays, and the future outlook for this material system.
InAs quantum dots embedded in InGaAs quantum wells with InAlAs barriers on InP substrate grown by
metalorganic chemical vapor deposition are utilized for high operating temperature detectors and focal plane arrays
in the middle wavelength infrared. This dot-well combination is unique because the small band offset between the
InAs dots and the InGaAs well leads to weak dot confinement of carriers. As a result, the device behavior differs
significantly from that in the more common dot systems that have stronger confinement. Here, we present energy
level modeling of our QD-QW system and apply these results to interpret the detector behavior. Detectors showed
high performance with D* over 1010 cmHz1/2/W at 150 K operating temperature and with high quantum efficiency
over 50%. Focal plane arrays have been demonstrated operating at high temperature due to the low dark current
observed in these devices.
We demonstrate optimization of continuous wave (cw) operation of 4.6 μm quantum cascade lasers (QCLs). A 19.7 μm
by 5 mm, double channel processed device exhibits 33% cw WPE at 80 K. Room temperature cw WPE as high as 12.5%
is obtained from a 10.6 μm by 4.8 mm device, epilayer-down bonded on a diamond submount. With the semi-insulating
regrowth in a buried ridge geometry, 15% WPE is obtained with 2.8 W total output power in cw mode at room
temperature. This accomplishment is achieved by systematically decreasing the parasitic voltage drop, reducing the
waveguide loss and improving the thermal management.
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