The Center for Quantum Devices in the News by    
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51.  
Accelerating adoption of GaN substrates for LED manufacture
Accelerating adoption of GaN substrates for LED manufacture
Compound Semiconductor Magazine - June 1, 2014
COMMERCIALISATION of the GaN LED can be traced back to the development of p-type doping of this wide bandgap semiconductor in the early 1990s. Since then, the performance of this device has improved exponentially, enabling it to progress from use in the backlighting of mobile screens to providing a source for solid-state lighting. However, although LED lighting is now commonplace, its cost-performance profi le has a long way to go untill the incumbent vacuum-tubebased lighting technologies will cease to dominate. One of today’s key bottlenecks is the requirement to use a ‘non-native’ substrate. A new substrate option that has attracted a signifi cant amount of attention is ZnO, which not only has the same crystal structure as GaN, but also very similar lattice parameters and comparable thermal expansion coefficients. ... [read more]
 
52.  
Razeghi Authors Technical Article in International Society for Optics and Photonics (SPIE)
Razeghi Authors Technical Article in International Society for Optics and Photonics (SPIE)
EECS Newsroom - January 10, 2014
Razeghi1-oct3 2Manijeh Razeghi, Walter P. Murphy Professor, Director, Center for Quantum Devices (CQD) wrote a featured technical article, titled, "Quantum Cascade Lasers for IR and THz Spectroscopy," that was published December 16, 2013, on the International Society for Optics and Photonics (SPIE) website for her recent research on demonstrating increased power, spectral coverage, and tunability of quantum cascade lasers. Prof. Razeghi's recent publication, focuses on how developing quantum cascade lasers (QCLs) with the highest power, efficiency, and tunability. Unlike traditional diode lasers, the QCL has a series of quantum wells, which split the usual electron bands into subbands. The QCL emits over several intersubband transitions in this structure. Her CQD team can engineer its optical response using quantum size effects, to achieve a highly variable emitting wavelength based on nanometer-scale control of the quantum well thickness. They demonstrated room-temperature QCLs covering both the 3–16μm and 65–300μm wavelength ranges using an indium phosphide (InP) material system. ... [read more]
 
53.  
Quantum cascade lasers for IR and THz spectroscopy
Quantum cascade lasers for IR and THz spectroscopy
SPIE Newsroom - December 22, 2013
Terahertz spectroscopy is widely used for chemical detection, and has applications in quality control for manufacturing, security screening, and astronomy. Most chemicals absorb in the mid-IR and THz spectral regions, which cover a wavelength range of 3–300 microns. During our research1 we developed quantum cascade lasers (QCLs) with the highest power, efficiency, and tunability. Unlike traditional diode lasers, the QCL has a series of quantum wells, which split the usual electron bands into subbands. The QCL emits over several intersubband transitions in this structure. We can engineer its optical response using quantum size effects, to achieve a highly variable emitting wavelength based on nanometer-scale control of the quantum well thickness. We demonstrated room-temperature QCLs covering both the 3–16μm and 65–300μm wavelength ranges. ... [read more]
 
54.  
Researchers Develop World’s Highest Quantum Efficiency UV Photodetectors
Researchers Develop World’s Highest Quantum Efficiency UV Photodetectors
McCormick Press Release - December 3, 2013
Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at McCormick, and her group have brought this AlxGa1-xN-based dream device closer to reality by developing a compact photodetector with the world’s highest quantum efficiency. This was achieved by refining the low-pressure metal-organic chemical-vapor-deposition growth as well as the UV photodetector p-i-n structure. A paper describing the results, “AlxGa1-xN-Based Back-Illuminated Solar-Blind Photodetectors with External Quantum Efficiency of 89%,” was published November 5 in the journal Applied Physics Letters. Although sapphire is the most common choice for back-illuminated devices, researchers also developed alternative low-cost UV photodetectors grown on silicon substrate. Razeghi’s group used a novel maskless Lateral Epitaxial Overgrowth (LEO) technique for the growth of a high-quality aluminum nitride (AlN) template layer on silicon substrate. Following the template growth, a p-i-n structure is grown and processed. This low-cost approach eventually led to the world’s first successful implementation of UV-PD structure grown on a silicon substrate. A paper describing the findings, “AlxGa1-xN-Based Solar-Blind Photodetector Based on Lateral Epitaxial Overgrowth of AlN on Si Substrate,” was published October 30 in the journal Applied Physics Letters. ... [read more]
 
55.  
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]
 
56.  
<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]
 
57.  
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]
 
58.  
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]
 
59.  
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]
 
60.  
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]
 

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