The Center for Quantum Devices in the News by    
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71.  
Stress-reduced solar-blind AlGaN-based FPA is crack-free
Stress-reduced solar-blind AlGaN-based FPA is crack-free
Laser Focus World, Vol. 49, No. 4, p. 14 - April 30, 2013
Focal-plane arrays (FOAs) that operate in the solar-blind spectral region (created by the absorption of light below 290 nm by atmospheric ozone)have uses in covert non-line-of-sight other forms of free space communications as well as UV spectroscopy, flame detection,and many other applications. With their extremely high rejection of the non-solar-blind spectrum , aluminum gallium nitride (AlGaN) -based structures are potentially excellent photodetecting candidates for solar blind FPAs. However this type of structures is difficult to fabricate without the formation of cracks. ... [read more]
 
72.  
Imager combines SWIR and MWIR sensitivity
Imager combines SWIR and MWIR sensitivity
Laser Focus World, Vol. 49, No. 2, p. 24-25 - February 27, 2013
Manijeh Razeghi and her group at Northwestern University have created High performance infrared (IR) image that combines detection in both the shortwave and midwave IR(SWIR and MWIR) in one device-a quality particularly valuable for tracking and reconnaissance. The device is based on a III-V semiconductor-based type-II indium arsenide/gallium antimonide (InAs/GaSb) superviously had only been implemented for MWIR and longwave IR (LWIR). Each pixel is made of an MWIR single heterodiode grown on top of a p-i-n SWIR homodiode, all fabricated on a GaSb substrate, which is subsequently removed for backside illumination (meaning the SWIR layer is on top). Crucially, the residual InAsSb etch-stop layer is also removed, using a citric-acid-based solution that etches away a specially inserted GaSb layer, eliminating the problem of the 4 µm InAsSb absorption-band edge. The prototype focal-plane array (FPA) has 320 256 pixels. ... [read more]
 
73.  
Northwestern tunes mid-infrared QCLs
Northwestern tunes mid-infrared QCLs
SPIE Photonics West Show Daily, p. 29 - February 6, 2013
The ongoing challenge of developing short-wavelength QCLs were described by Neelanjan Bandyopad hyay of Northwestern University in an OPTO Session on the topic. “Wave-lengths of 3 to 3.5 microns are important for several different spectroscopy applications, because it coincides with many hydrocarbon absorbtion bands,” he said. Of the candidate semiconductor system, InGaAs-InAlAs on InP is the best choice on balance for short wavelength QCLs according to Northwestern research. Using it has allowed the development of the first room-temprature continuous wave QCLs in the target wavelength band, although the same system can additionally cover the entire 3-16 micron range under appropriate conditions. Daylight Solutions has demonstrated a broadly-tunable high-resolution CW laser based on its QC devices. “Broad tuning capability allows the identification of multiple chemical species in spectroscopy applications, while narrow linewidth facilitates the high spectral resolution that spectroscopy requires, “commented Leigh Bromely. The company’s external-cavity system, called ECqcl, uses a grating to tune the QCL output and control the tuning performance, and a unique cavity geometry that enforces one mode during operation. ... [read more]
 
74.  
Light or no light-this new infrared camera captures images
Light or no light-this new infrared camera captures images
Medill Reports-Chicago / Medill News Service - January 29, 2013
The center has developed detectors that are a complex quantum structure. The devices are expected to be valuable for military, medical and civilian purposes. http://news.medill.northwestern.edu/chicago/news.aspx?id=214663 ... [read more]
 
75.  
Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
R&D Magazine - January 16, 2013
High-performance infrared cameras are crucial for civilian and military applications such as night-vision goggles and search-and-rescue operations. Existing cameras usually fall into one of two types: active cameras, which use an invisible infrared source to illuminate the scene, usually in the near or short-wavelength infrared; and passive cameras, which detect the thermal radiation given off by a warm object, typically in the mid- or long-wavelength infrared, without the need for any illumination. Both camera types have advantages and disadvantages in the field. Read more at http://www.rdmag.com/news/2013/01/researchers-develop-integrated-dual-mode-active-and-passive-infrared-camera?et_cid=3044524&et_rid=54751184&linkid=http%3a%2f%2fwww.rdmag.com%2fnews%2f2013%2f01%2fresearchers-develop-integrated-dual-mode-active-and-passive-infrared-camera ... [read more]
 
76.  
Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
Researchers Develop Integrated Dual-mode Active and Passive Infrared Camera
News from McCormick - January 14, 2013
In a move that may change the way we look a two-color imaging, researchers at the Northwestern University’s Center for Quantum Devices have now found a way to integrate active and passive infrared imaging capability into a single chip. This opens the way to lighter and simpler dual-mode active/passive cameras with lower power dissipation. A paper about the findings, “Active and Passive Infrared Imager Based on Short-Wave and Mid-Wave Type-II Superlattice Dual-Band Detectors,” was published January 1 in the journal Optic Letters. The work was led by Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science in Northwestern’s McCormick School of Engineering and Applied Science. The researchers achieved this feat by engineering the quantum properties of novel semiconductor materials called the indium arsenide/gallium antimonide (InAs/GaSb) type-II superlattices. Researchers at the center have been pioneering the development of type-II superlattices as a superior replacement of aging mercury-cadmium-telluride (HgCdTe) infrared camera technology in terms of both performance and cost. Using the unique band-structure engineering capabilities of type-II superlattices, they have developed a new structure incorporating two different superlattices with different layer spacings, thus enabling detection with a cutoff wavelength of either 2.2µm (active mode) or 4.5µm (passive mode). This new device can simply switch from passive to active mode by a very small change in bias. The work was funded by the Defense Advanced Research Projects Agency. ... [read more]
 
77.  
Lasers improved for standoff sensing
Lasers improved for standoff sensing
Photonics Spectra - November 1, 2012
A new resonator design that controls both wavelength and beam quality enables the purest, brightest and most powerful beams ever from a single-mode infrared quantum cascade laser. Manijeh Razeghi, the Walter P. Murphy Professor of Electrical Engineering and Computer Science at Northwestern University’s McCormick School of Engineering and Applied Sciences, and colleagues developed the resonator using a new type of distributed feedback mechanism called B-DFB, a simple diffractive feedback in an angled laser cavity. The work improves the accuracy of the devices, critical for boosting the standoff detection of gas, explosives or other hazardous materials to even greater distances. The findings appeared in Applied Physics Letters (doi: 10.1063/1.4747447). ... [read more]
 
78.  
Researchers Develop Simplified Approach for High-Power, Single-Mode Lasers
Researchers Develop Simplified Approach for High-Power, Single-Mode Lasers
McCormick News Article - August 23, 2012
When it comes to applications like standoff sensing—using lasers to detect gas, explosives, or other materials from a safe distance—the laser’s strength is of the utmost importance. A stronger and purer beam means devices can sense danger more accurately from a greater distance. Northwestern University researchers have developed a new resonator that that controls both wavelength and beam quality, creating the purest, brightest, and most powerful single-mode quantum cascade lasers yet at the 8-12 micron range. The feat is achieved through the use of a new type of “distributed feedback” mechanism called Β-DFB, a simple diffractive feedback in an angled laser cavity. A paper describing the findings, “Angled Cavity Broad Area Quantum Cascade Lasers,” was published August 21 in the journal Applied Physics Letters ( DOI:10.1063/1.4747447). ... [read more]
 
79.  
Improved LEDs and photovoltaics by hybridization and nanostructuring
Improved LEDs and photovoltaics by hybridization and nanostructuring
SPIE Newsroom - June 15, 2012
There has been rapid industrial development for optoelectronic devices based on III-Nitrides, which span a direct bandgap from deep UV to IR, and are currently widely used in commercial white, UV, blue, and green LEDs. This alloy system is now projected to provide a platform for the development of novel multi-junction photovoltaics (PVs) with an unprecedented fit to the solar spectrum. However, improving the efficiency of InGaN-based p-n junctions is a very complex and multifaceted task for a number of reasons.
Zinc oxide (ZnO) is a remarkable, multifunctional, and biocompatible direct-, wide-bandgap semiconductor, with a distinctive property set and a unique potential for nanostructuring. Recently, there has been a surge of activity surrounding ZnO to the point where the number of publications now rivals that for GaN. Due to their similar crystal structures and bandgaps, ZnO and GaN can be combined in new ways, which opens up the prospect of novel optoelectronic devices and has the potential to solve many of the issues with existing III-Nitride devices. ... [read more]

 
80.  
Superlattice sees colder objects in two colors and high resolution
Superlattice sees colder objects in two colors and high resolution
SPIE Newsroom - February 10, 2012
The capabilities of IR sensing, commonly used for night vision, have been extended to see colder objects at high speed and potentially made cheaper by using a semiconductor material called the type II superlattice. The wavelength tunability and material robustness of type III-V superlattice have generated much attention in recent years. This is especially true with respect to the performance of the material in narrow-energy-gap detectors, and specifically in a part of the electromagnetic spectrum between 8 and 12 μm, called the long-wavelength IR (LWIR). The benefits of this technology have enabled us to push type II superlattice to its logical next step: a camera capable of seeing distinct wavebands or colors in an all-in-one package, a feat not previously demonstrated by this material system in the LWIR. Our group engineered the detection energies on the cameras to be extremely narrow, with cutoff wavelengths at 9.5 and 13 μm, in the range of roughly 0.1eV in energy. Realizing the camera was a difficult task because the light-absorbing layers are prone to surface leakage effects due to the size of the pixels, which are 30μm wide. We first reported a dual-band LWIR 320256 pixel-sized type II superlattice in July 2011. More recently, we also demonstrated a large-format 640 x 512 pixel type II superlattice camera based on the same material design. The 4x increased resolution is necessary for many advanced applications. ... [read more]
 

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