The Center for Quantum Devices in the News by    
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51.  
CQD Research Highlighted on the Cover
CQD Research Highlighted on the Cover
Physica Status Solidi C - October 14, 2013
Self-forming, vertically-aligned, arrays of black-body-like ZnO moth-eye nanostructures were grown on Si(111), c-Al2O3, ZnO and high manganese austenitic steel substrates using Pulsed Laser Deposition. X-ray diffraction (XRD) revealed the nanostructures to be well-crystallised wurtzite ZnO with strong preferential c-axis crystallographic orientation along the growth direction for all the substrates. Cathodoluminescence (CL) studies revealed emission characteristic of the ZnO near band edge for all substrates. Such moth-eye nanostructures have a graded effective refractive index and exhibit black-body characteristics. Coatings with these features may offer improvements in photovoltaic and LED performance. Moreover, since ZnO nanostructures can be grown readily on a wide range of substrates it is suggested that such an approach could facilitate growth of GaN-based devices on mismatched and/or technologically important substrates, which may have been inaccessible till present. ... [read more]
 
52.  
<a href=SOLID-STATE DEEP UV EMITTERS/DETECTORS: Zinc oxide moves further into the ultraviolet" src="news/LFW_SOLID-STATE_DEEP_UV_EMITTERS_DETECTORS.jpg">
SOLID-STATE DEEP UV EMITTERS/DETECTORS: Zinc oxide moves further into the ultraviolet
Laser Focus World - October 10, 2013
Zinc oxide (ZnO) is a remarkable, multifunctional semiconducting material with a direct, wide bandgap energy (Eg ~ 3.4 eV), intrinsically high transparency over the whole visible range, and a resistivity that can be tuned from semi-insulating right through to semi-metallic by doping. In photovoltaics, ZnO is currently displacing indium tin oxide for use as a transparent conducting electrical contact due to recent improvements in conductivity obtainable with aluminium-doped ZnO, combined with processing, cost, and toxicity advantages. Alloys of ZnO with magnesium (MgxZn1-xO) have been explored as an alternative to (Al)GaN for UV LED applications. For fabricating (Mg)ZnO-based solar-blind photodetectors, Mg content should be at least 45%, but many studies have found that phase segregation of rock-salt phase MgO appears when Mg content is over 36 at %. Recently, however, single-phase wurtzite layers with Mg concentrations over 49 at % were prepared through strain engineering at the substrate interface by means of buffer layers (ZnO and strontium tin oxide—SrTiO3—or bulk ZnO substrates). ... [read more]
 
53.  
Northwestern Researchers Develop Compact, High-Power Terahertz Source at Room Temperature
Northwestern Researchers Develop Compact, High-Power Terahertz Source at Room Temperature
News from McCormick - October 3, 2013
Terahertz (THz) radiation — radiation in the wavelength range of 30 to 300 microns — is gaining attention due to its applications in security screening, medical and industrial imaging, agricultural inspection, astronomical research, and other areas. Traditional methods of generating terahertz radiation, however, usually involve large and expensive instruments, some of which also require cryogenic cooling. A compact terahertz source — similar to the laser diode found in a DVD player —operating at room temperature with high power has been a dream device in the terahertz community for decades. ... [read more]
 
54.  
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]
 
55.  
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]
 
56.  
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]
 
57.  
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]
 
58.  
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]
 
59.  
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]
 
60.  
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]
 

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