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Home > Press > Nanostructures promise big impact on higher-speed, lower-power optical devices: University of Cincinnati physicists are seeing big potential in small semiconductor nanowires for improved optical infrared sensor technologies Abstract: With new technology getting smaller and smaller, requiring lower power, University of Cincinnati physics research points to new robust electronic technologies using quantum nanowire structures. The semiconductor nanowires may lead to advances in sensitive electronic technology including heat detecting optical infrared sensors and biomedical testing, all of which can fit inside small electrical devices. Supported by multiple National Science Foundation grants, the UC research team is working with a collaborative team of physicists, electronic materials engineers and doctoral students from around the world -- all to perfect the growth and development of crystalline nanowires that could form the backbone of new nanotechnologies. But to fully apply this technology to modern devices, UC researchers are first looking closely -- on a fundamental level -- at how energy is distributed and measured along thin-strand nanowires so small that thousands of them could theoretically fit inside a human hair. "Now that we know the technology can be developed, we need to understand exactly how the electrical processes work inside the nanowire cores," say Howard Jackson and Leigh Smith, professors of physics at the University of Cincinnati. "After finally perfecting a standardized process for growing and developing crystalline nanowire fibers with our partners at the Australian National University in Canberra, we have been able to take it one step further. "Using a combination of materials like indium gallium arsenide and indium phosphide, we can develop thin nanowire cores with protective outer shells." It turns out that these unique nanowire materials have unusually large spin orbit interactions, which the researchers find can conduct electricity really well and may allow the use of spin to enable new computing paradigms. Jackson and Smith are presenting these findings at the American Physical Society Conference, in Baltimore, March 16, titled, "Exploring Dynamics and Band Structure in Mid Infrared GaAsSb and GaAsSb/InP Nanowire Heterostructures." SMALL YET MIGHTY The researchers claim the secret to the success of this multi-collaborative effort is in the combination of materials used to create the nanowires. Initially grown at the Australian National University in Canberra, the nanowires are sprouted from a combination of beads of molten gold scattered across a particular surface. As the process is heated inside a chamber using indium gallium arsenide gases, long microscopically thin core fibers sprout up from between the controlled surface environment. Other material combinations are then introduced to form an outer shell acting as a sheath around each core, resulting in quantum nanowire semiconducting heterostructures all uniform in size, shape and behavior. After the fibers are shipped across the globe to Cincinnati, Jackson, Smith and their team of doctoral students are then able to use sophisticated equipment to measure the electrical and photovoltaic potentials of each fiber along its surface. In earlier research, the collaborative team found extrinsic and intrinsic problems when the fiber cores did not have the outer sheath-like shells. "If we don't have this outer sheath, the nanowires have a very short energy lifetime, says Jackson. "When we surround the core with this sheath, the energy lifetime can go up by an order or two orders of magnitude." And while gallium arsenide alone is a very common semiconductor, its energy gap is large and in the visible range, which absorbs light. To achieve success in detecting optical heat or infrared, the team says using indium gallium arsenide fibers have smaller energy gaps that can be used successfully in optical detector devices. doctoral student in physics lab with laser lights "The goal for one of our research equipment grants is to work with the local L3 Cincinnati Electronics Company, which makes infrared (small gap) detectors for night-vision imaging for military applications," says Smith. "Future direct applications for this type of technology also include medical devices that detect body heat, as well as remote sensors installed in iphones that can be used for environmental purposes that detect and measure heat loss in houses." The researchers say this new nanowire technology is unique because it can turn different wavelengths of light into an electrical signal, and in this case it means turning an infrared light into an electric signal that can be measured. Smith explains that with the geometry of the nanowires you can have a long axis running the length of the wire, which gives you lots of possibilities for absorption as the light comes down, but then you also have this very small diameter. "When contacts are interspersed along either side, essentially then the electrons in the holes don't have to travel very far before they are collected," says Smith. "So in principle it can become a more effective detector as well as a more effective solar cell." SMALL DIMENSION NANOWIRES "When you get to very small dimensions in nanowires that are small in diameter, but are a few microns long, those properties then change and can show quantum properties and become almost one-dimensional," says Jackson. "The physics then changes as you change those sizes." Jackson and Smith found that the nanowire's ultra-thin outer shells functioned best at widths of four to eight nanometers, which is 25,00 and 12,500 times smaller respectively, than the diameter of a human hair. When looking at the overarching benefits of working with microscopic nanostructures the researchers see tremendous potential for its ability to pack much more high-energy efficiency into small devices with finite space. It's getting closer to a win-win for everyone, they're saying, especially when this research enters the next stage, bringing it closer to functioning inside electronic and optical sensor devices. "Our fundamental investigation is still a step away from a direct optical device application," says Jackson. "But you can clearly see over time that this collaborative research has made an impact." ### Additional contributors to the research are UC physics doctoral students, Nadeeka Wickramasuriya, Yuda Wang and Samuel Linser. Collaborators from the Australian National University in Canberra, Department of Electronic Materials Engineering, are Xiaoming Yuan, Philippe Caroff, Hoe Tan and Chennupati Jagadish. NSF FUNDING * NSF "Major Research Instrumentation: Development of a Mid-infrared Optical Microscope for Investigation of Femtosecond Dynamics of Single Large Spin Orbit Semiconductor Heterostrucutures," Leigh Smith and Howard Jackson, $492,983 plus cost sharing of $201,798 or a total of $694,781. * NSF "MRI: Acquisition of a Ultra-High Resolution Analytical Scanning Electron Microscope for Multidisciplinary Research and Education," V. Vasudevan, PI, several co-PIs including L. Smith and H. Jackson, $531,693 plus significant cost sharing from the State of Ohio and CEAS and A&S to bring the total to >$900,000. * NSF "GOALI: Infrared Nanowire Heterostructures: Fundamentals and Emerging Detector Applications," Leigh Smith and Howard Jackson, $400,000. * NSF DMR "Carrier and Spin Dynamics in Large Spin-Orbit Semiconductor Nanowire Heterostructures," Leigh Smith and Howard Jackson, $489,551. Teaching and Broader Impacts: * NSF-IUSE "Enhancing Student Success in Biology, Chemistry, and Physics by Transforming the Faculty Culture," H. Jackson, PI, $97,148. This grant is provided as a supplement to a presently funded grant for Biology, Chemistry, and Physics so that the Department of Mathematics can be included in these efforts. The currently funded grant is NSF-IUSE "Enhancing Student Success in Biology, Chemistry, and Physics by Transforming the Faculty Culture," $643,000, 9/01/2014 - 8/31/2018, Howard Jackson (PI). * NSF Collaborative Research: Resource and Repository: Broader Impacts of the NSF-CMP Program, Leigh Smith and others $150,000. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.


Nichols J.M.,U.S. Navy | Waterman J.R.,U.S. Navy | Menon R.,Remote Reality Inc. | Devitt J.,L3 Cincinnati Electronics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

A high-resolution mid-wave infrared panoramic periscope sensor system has been developed. The sensor includes a catadioptric optical system that provides a 360° horizontal azimuth by -10° to +30° elevation field of view without requiring moving components (e.g. rotating mirrors). The focal plane is a 2048 x 2048, 15μm pitch InSb detector operating at 80K. An on-board thermo-electric reference source allows for real-time nonuniformity correction using the two-point correction method. The entire system (detector-dewar assembly, cooler, electronics and optics) is packaged to fit in an 8'' high, 6.5'' diameter volume. This work describes both the system optics and electronics and presents sample imagery. We also discuss the sensor's radiometric performance, quantified by the NEDT, as a function of key system parameters. The ability of the system to resolve targets as a function of imaged spatial frequency is also presented. © 2010 Copyright SPIE - The International Society for Optical Engineering.


The tiny miracle fibers may lead to advances in sensitive electronic technology including heat detecting optical infrared sensors and biomedical testing, all of which can fit inside small electrical devices. Supported by a battery of NSF grants, the UC research team has worked with a collaborative team of physicists, electronic materials engineers and doctoral students from around the world –– all to perfect the growth and development of crystalline nanowire fibers that form the backbone of nanotechnology. But to fully apply this technology to modern devices, UC researchers are first looking closely –– on a fundamental level –– at how energy is distributed and measured along thin-strand nanowires so small that thousands of them could theoretically fit inside a human hair. "Now that we know the technology can be developed, we need to understand exactly how the electrical processes work inside the nanowire cores," say Howard Jackson and Leigh Smith, professors of physics at the University of Cincinnati. "After finally perfecting a standardized process for growing and developing crystalline nanowire fibers with our partners at the Australian National University in Canberra, we have been able to take it one step further. "Using a combination of materials like indium gallium arsenide, we can develop thin nanowire cores with protective outer shells." Even with incredibly small masses, it turns out that the unique nanowires have unusually large spin orbit interactions, which the researchers find can conduct electricity really well and may help improve heat sensing infrared detectors for small military devices. Jackson and Smith are presenting these remarkable findings at the American Physical Society Conference, in Baltimore, March 16, titled, "Exploring Dynamics and Band Structure in Mid Infrared GaAsSb and GaAsSb/InP Nanowire Heterostructures." The researchers claim the secret to the success of this multi-collaborative effort is in the combination of materials used to create the nanowires. Initially grown at the Australian National University in Canberra, the nanowires are sprouted from a combination of beads of molten gold scattered across a particular surface. As the process is heated inside a chamber using indium gallium arsenide gases, long microscopically thin core fibers sprout up from between the controlled surface environment. Other material combinations are then introduced to form an outer shell acting as a sheath around each core, resulting in quantum nanowire semiconducting heterostructures all uniform in size, shape and behavior. After the fibers are shipped across the globe to Cincinnati, Jackson, Smith and their team of doctoral students are then able to use sophisticated equipment to measure the electrical and photovoltaic potentials of each fiber along its surface. In earlier research, the collaborative team found extrinsic and intrinsic problems when the fiber cores did not have the outer sheath-like shells. "If we don't have this outer sheath, the nanowires have a very short energy lifetime, says Jackson. "When we surround the core with this sheath, the energy lifetime can go up by an order or two orders of magnitude (power in watts)." And while gallium arsenide alone is a very common semiconductor, its energy gap is large and in the visible range, which absorbs light. To achieve success in detecting optical heat or infrared, the team says using indium gallium arsenide fibers produce smaller energy gaps that can be used successfully in optical detector devices. "The goal for one of our research equipment grants is to work with the local L3 Cincinnati Electronics Company, which makes infrared (small gap) detectors for night-vision imaging for military applications," says Smith. "Future direct applications for this type of technology also include medical devices that detect body heat, as well as remote sensors installed in iphones that can be used for environmental purposes that detect and measure heat loss in houses." The researchers say this new nanowire technology is particularly unique because it can turn different types of light into an electrical signal, and in this case it means turning an infrared light into an electric signal that can be measured. Smith explains that with the geometry of the nanowires you can have a long axis running the length of the wire, which gives you lots of possibilities for absorption as the light comes down, but then you also have this very small diameter. "When contacts are interspersed along either side, essentially then the electrons in the holes don't have to travel very far before they are collected," says Smith. "So in principle it can become a more effective detector as well as a more effective solar cell." "When you get to very small dimensions in nanowires that are small in diameter, but are a few microns long, those properties then change and can show a quantum (finite number) of properties and become almost one-dimensional," says Jackson. "The physics then changes as you change those sizes." Jackson and Smith found that the nanowire's ultra-thin outer shells functioned best at widths of four to eight nanometers, which is 25,00 and 12,500 times smaller respectively, than the diameter of a human hair. When looking at the overarching benefits of working with microscopic nanostructures the researchers see tremendous payback potential for its ability to pack much more high-energy efficiency into small devices with finite space. It's getting closer to a win-win for everyone, they're saying, especially when this research enters the next stage, bringing it closer to functioning inside electronic and optical sensor devices. "Our fundamental investigation is still a step away from a direct optical device application," says Jackson. "But you can clearly see over time that this collaborative research has made an impact." Explore further: Researchers demonstrate quantum dots that assemble themselves


Choi K.K.,U.S. Army | Jhabvala M.D.,NASA | Forrai D.P.,L3 Cincinnati Electronics | Sun J.,U.S. Army | Endres D.,L3 Cincinnati Electronics
Infrared Physics and Technology | Year: 2011

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (C-QWIP FPAs) into the far infrared regime. Specifically, we are developing the detectors for the thermal infrared sensor (TIRS) used in the NASA Landsat Data Continuity Mission. This mission requires infrared detection cutoff at 12.5 μm and FPAs operated at ∼43 K. To maintain a low dark current in these extended wavelengths, we adopted a low doping density of 0.6 × 1018 cm-3 and a bound-to-bound state detector in one of the designs. The internal absorption quantum efficiency η is calculated to be 25.4% for a pixel pitch of 25 μm and 60 periods of QWs. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external η is 14.4%. To yield the theoretical conversion efficiency CE, the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1 × 10-6 A/cm2 at 43 K. For regular infrared imaging above 8 μm, the FPA will have a noise equivalent temperature difference (NETD) of 16 mK at 2 ms integration time in the presence of 260 read noise electrons, and it increases to 22 mK at 51 K. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30-μm cutoff, which will be useful for the Jupiter-Europa deep space exploration. In this work, we also investigated the C-QWIP optical coupling when the detector substrate is thinned. © 2010 Elsevier Ltd. All rights reserved.


Choi K.-K.,U.S. Army | Sun J.,NASA | Jhabvala M.D.,L3 Cincinnati Electronics | Forrai D.P.,U.S. Army | Endres D.W.,L3 Cincinnati Electronics
Optical Engineering | Year: 2011

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (FPAs) into the far infrared regime. Specifically, we are developing the detectors for the thermal infrared sensor (TIRS) used in the Landsat Data Continuity Mission. To maintain a low dark current, we adopted a low doping density of 0.6×1018cm 3 and a bound-to-bound state detector. The internal absorption quantum efficiency (QE) is calculated to be 25.4%. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external QE is 14.4%. To yield the theoretical conversion efficiency (CE), the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1×106 A/cm2 at 43 K. For regular infrared imaging above 8 μm, the FPA will have an noise equivalent temperature difference (NETD) of 16 mK at 2 ms integration time in the presence of 260 read noise electrons. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30 μm cutoff. © 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).


Choi K.K.,U.S. Army | Jhabvala M.D.,NASA | Forrai D.P.,L3 Cincinnati Electronics | Waczynaski A.,NASA | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012

Rigorous electromagnetic field modeling is applied to calculate the quantum efficiency (QE) of various quantum well infrared photodetector (QWIP) geometries. We found quantitative agreement between theory and experiment for linear grating coupled QWIPs, cross-grating coupled QWIPs, corrugated-QWIPs, and enhanced-QWIPs. Also, the model adequately explains the spectral lineshapes of the quantum grid infrared photodetectors. Equipped with a quantitative model, we designed resonant cavities that are suitable for narrowband imaging around 8 - 9 microns. The results show that with properly designed structures, the theoretical QE can be as high as 78% for 25-micron pixel pitch arrays and 46% for 12-micron pixel pitch arrays. Experimental efforts are underway. © 2011 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).


Choi K.K.,U.S. Army | Jhabvala M.D.,NASA | Forrai D.P.,L3 Cincinnati Electronics | Waczynski A.,NASA | And 2 more authors.
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2011

Rigorous electromagnetic (EM) field modeling is applied to calculate the external quantum efficiency (QE) of various quantum well infrared photodetector (QWIP) pixel geometries with thinned substrates. We found that for a 24 × 24 × 1.5 μm3 cross-grating QWIP, the QE is peaked at 13.0, 11.0, and 8.4 μm, insensitive to the grating periods. These peaks are identified as the first three harmonic resonances associated with the pixel resonant cavity. For a regular prismshaped corrugated QWIP (C-QWIPs) with a 25-μm pitch, the QE oscillates about its classical value of 24.5% within the calculated wavelength range from 3 to 15 μm. A peaked value of 32% occurs at 9.1 μm. For pyramidal C-QWIPs, the maximum QE is 42%, and for cone-shaped C-QWIPs, it is 35%. In the presence of an anti-reflection coating, the oscillation amplitude diminishes, and the average values generally rise to near the peaks of the oscillations. The modeling results are compared with the experimental data for grating QWIP focal plane arrays (FPAs) and prismshaped C-QWIP FPAs; satisfactory agreements were achieved for both. After verifying our EM approach, we explored other detector geometries and found new types of resonator QWIPs (R-QWIPs) that can provide 30% QE at certain wavelengths on a 1.5-μm-thick active material. Combining the high QE of a resonator and the high gain of a thin material layer, the new R-QWIPs will have a conversion efficiency far higher than the existing QWIP detectors. The present resonator approach will also have an impact on other detector technologies. © 2011 SPIE.


Choi K.K.,U.S. Army | Jhabvala M.D.,NASA | Forrai D.P.,L3 Cincinnati Electronics | Sun J.,U.S. Army | Endres D.,L3 Cincinnati Electronics
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2010

We have extended our investigation of corrugated quantum well infrared photodetector focal plane arrays (C-QWIP FPAs) into the far infrared regime. Specifically, we are developing the detectors for the Thermal Infrared Sensor (TIRS) used in the Landsat Data Continuity Mission. This mission requires infrared detection cutoff at 12.5 μm and FPAs operated at 43 K. To maintain a low dark current in these extended wavelengths, we adopted a low doping density of 0.6 × 1018 cm-3 and a bound-to-bound state detector in one of the designs. The internal absorption QE is calculated to be 25.4% for a pixel pitch of 25 microns and 60 periods of QWs. With a pixel fill factor of 80% and a substrate transmission of 70.9%, the external QE is 14.4%. To yield the theoretical conversion efficiency CE, the photoconductive gain was measured and is 0.25 at 5 V, from which CE is predicted to be 3.6%. This value is in agreement with the 3.5% from the FPA measurement. Meanwhile, the dark current is measured to be 2.1 × 10-6 A/cm2 at 43 K. For regular infrared imaging above 8 μm, the FPA will have an NETD of 16 mK at 2 ms integration time in the presence of 260 read noise electrons, and it increases to 22 mK at 51 K. The highest operability of the tested FPAs is 99.967%. With the CE agreement, we project the FPA performance in the far infrared regime up to 30 μm cutoff. © 2010 Copyright SPIE - The International Society for Optical Engineering.


Nichols J.M.,U.S. Navy | Waterman J.R.,U.S. Navy | Menon R.,RemoteReality Corporation | Devitt J.,L3 Cincinnati Electronics
Optical Engineering | Year: 2010

A high-resolution midwave infrared panoramic periscope sensor system has been developed. The sensor includes an f2.5 catadioptric optical system that provides a field of view with 360-deg horizontal azimuth and -10- to 30-deg elevation without requiring moving components (e.g., rotating mirrors). The focal plane is a 20482048, 15-μm-pitch InSb detector operating at 80 K. An onboard thermoelectric reference source allows for real-time nonuniformity correction using the two-point correction method. The entire system (detector-Dewar assembly, cooler, electronics, and optics) is packaged to fit in an 8-in.-high, 6.5-in.-diameter volume. This work describes both the system optics and the electronics and presents sample imagery. We model both the sensors radiometric performance, quantified by the noise-equivalent temperature difference, and its resolution performance. Model predictions are then compared with estimates obtained from experimental data. The ability of the system to resolve targets as a function of imaged spatial frequency is also presented. © 2010 Society of Photo-Optical Instrumentation Engineers.

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