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Quantum Confined Semiconductor Nanostructures

作者： Workman, Clayton L. Wang, Zhiming Ma, Wenquan George, Christi E. Selvam, R. Panneer Salamo, Gregory J. Zhou, Qiaoying Manasreh, M. Omar C-SPIN Microelectronics-Photonics Program University of Arkansas Fayetteville AR 72701 United States Dept. of Electrical and Comp. Eng. University of New Mexico Albuquerque NM 87131 United States

We report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.

关键词： Semiconductor quantum wells

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Plasmon optics and thermal dissipation in nanocomposite thin films

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MRS Online Proceedings Library (OPL) 2015年第1期1788卷 23-28页

作者： Jeremy R. Dunklin Gregory T. Forcherio Keith R. Berry Jr. D.K. Roper Department of Chemical Engineering University of Arkansas Fayetteville AR 72701 MicroElectronics-Photonics Graduate Program University of Arkansas Fayetteville AR 72701

Optical properties and thermal relaxation dynamics of resonantly excited plasmons are important in applications for optoelectronics, biomedicine, energy, and catalysis. Geometric optics of polydimethylsiloxane (PDMS) thin films containing uniformly or asymmetrically distributed polydisperse reduced AuNPs or uniformly distributed monodisperse solution-synthesized AuNPs were recently evaluated using a compact linear algebraic sum. Algebraic calculation of geometric transmission, reflection, and attenuation for AuNP-PDMS films provides a simple, workable alternative to effective medium approximations, computationally expensive methods, and fitting of experimental data. This approach allows for the summative optical responses of a sequence of 2D elements comprising a 3D assembly to be analyzed. Thin PDMS films containing 3-7 micron layers of reduced AuNPs were fabricated with a novel diffusive-reduction synthesis technique. Rapid diffusive reduction of AuNPs into asymmetric PDMS thin films provided superior photothermal response relative to thicker films with AuNPs reduced throughout, with a photon-to-heat conversion of up to 3000°C/watt which represents 3-230-fold increase over previous AuNP-functionalized systems. Later work showed that introduction of AuNPs into PDMS enhanced thermoplasmonic dissipation coincident with internal reflection of incident resonant irradiation. Measured thermal emission and dynamics of AuNP-PDMS thin films exceeded emission and dynamics attributable by finite element analysis to Mie absorption, Fourier heat conduction, Rayleigh convection, and Stefan-Boltzmann radiation. Refractive-index matching experiments and measured temperature profiles indicated AuNP-containing thin films internally reflected light and dissipated power transverse to the film surface. Enhanced thermoplasmonic dissipation from metal-polymer nanocomposite thin films could affect opto- and bio-electronic implementation of these systems.

关键词： polymer Au film

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Creating an industrial work group atmosphere in technology graduate programs: An unexpected impact on minority success in graduate school

Creating an industrial work group atmosphere in technology g...

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113th Annual ASEE Conference and Exposition, 2006

作者： Vickers, Ken Foster, Ron Salamo, Greg University of Arkansas United States Department of Physics University of Arkansas United States Interdisciplinary Microelectronics-Photonics Graduate Program Basore Endowed Department of Physics University of Arkansas United States Optical Society of America United States

The interdisciplinary graduate program in microelectronics-photonics (microEP) was created at the University of Arkansas in the fall of 1998 to merge traditional graduate research and educational excellence with specific training in operational effectiveness methods, intra and entrepreneurial skills, and teaming and group dynamics practice. The stated goal of this approach was to create a graduate program that emulates the industrial work group environment, with the group objective being that every graduate student achieves the highest academic training of which he or she is capable. In the seven years since the microEP grad program was started, this educational experiment in creating a graduate program centered in a natural work group culture has proven beneficial to its students - and has even been largely adopted by the UA Physics graduate program1. What was not expected is that this natural work group approach also created a graduate community that has acted to bridge minority students from the heavily supportive MSI atmosphere to the generally impersonal atmosphere found in white majority research intensive grad programs. Including the fall 2005 entering microEP Cohort 8 students, one hundred and three students are currently enrolled or graduated. This includes seventeen minority students, a percentage half again as high as the national average of graduating minority PhD students2and much higher than the current enrollment in the traditional UA science and engineering graduate programs. Two African-American men have completed their PhD microEP degrees, with one joining Virginia Commonwealth University as a tenure track faculty member, and the second currently enrolled in the University of Alabama Birmingham Medical School. In this paper the authors will first discuss methods that have been used to locate students in communities underrepresented in science and engineering that would be well served by the microEP research and educational training. The authors wil

关键词： Engineering education

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Simulation, fabrication, and measurement of a plasmonic-enhanced terahertz photoconductive antenna 9

Simulation, fabrication, and measurement of a plasmonic-enha...

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Terahertz, RF, Millimeter, and Submillimeter-Wave Technology and Applications IX

作者： Burford, Nathan El-Shenawee, Magda Microelectronics-Photonics Program University of Arkansas 731 W. Dickson St. FayettevilleAR72701 United States Department of Electrical Engineering 3217 Bell Engineering Center FayettevilleAR72701 United States

ISBN: (纸本)9781628419825

In this work a new plasmonic thin-film based terahertz photoconductive antenna is proposed. The computational method utilized to design the antenna is outlined, as well as the steps and preliminary results for the fabrication and characterization of the device. The model predicted over two orders of magnitude increase in the peak photocurrent as compared to a conventional device design, while slightly reducing the width of the induced current pulse. This indicates that the proposed design will be effective as a high efficiency terahertz emitter. In addition to the computational modeling, preliminary results demonstrating the proposed fabrication processes and experimental characterization are presented. It is demonstrated that when using a pyroelectric detector to quantify the output terahertz power it is important to first quantify the power of the IR photons generated by thermal relaxation in the device. © 2016 SPIE.

关键词： Finite element method

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Analysis of nanoscale deformation in GaAs(100): Towards patterned growth of quantum dots

Analysis of nanoscale deformation in GaAs(100): Towards patt...

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2005 materials Research Society Spring Meeting

作者： Taylor, Curtis R. Stach, Eric A. Malshe, Ajay P. Salamo, Gregory Department of Physics Microelectronics-photonics Program University of Arkansas Fayetteville AR 72703 United States National Center for Electron Microscopy Materials Science Division Lawrence Berkeley National Laboratory Berkeley CA 94720 United States Department of Mechanical Engineering Microelectronics-photonics Program University of Arkansas Fayetteville AR 72703 United States Department of Physics University of Arkansas Fayetteville AR 72703 United States School of Materials Engineering Purdue University West Lafayette IN 47907 United States

Nanoindentations were created in the GaAs(100) surface to act as strain centers for the controlled nucleation and patterning of InAs quantum dots. A systematic approach is taken to understand the indent deformation processes that may lead to precision patterning capabilities for a broad range of nanostructures. Indents were generated using loads below 450 μN with a sharp cube corner indenter. Site-specific cross-sectional thinning of nanoindents (down to 100 nm in size) has been achieved using the in-situ 'lift-out' technique. This allowed for observation of subsurface deformation by transmission electron microscopy (TEM). The crystal was observed to deform solely by dislocation activity with no evidence of amorphization, twinning, fracture, or phase transformation. It is shown that the single phase deformation of GaAs can be well characterized and controlled, which should allow for exploitation of the dislocation strain field to bias nucleation of self-assembled quantum dots. © 2005 Materials Research Society.

关键词： Nanostructured materials

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Optimization of nanotoroid arrays for plasmonic solar cell applications

Optimization of nanotoroid arrays for plasmonic solar cell a...

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IEEE International Symposium on Antennas and Propagation

作者： N. M. Burford M. El-Shenawee Computational Electromagnetics Group Microelectronics-Photonics Program University of Arkansas Department of Electrical Engineering University of Arkansas

ISBN: (纸本)9781467353168

This work presents the optimization of silver plasmonic nanotoroids in an infinite square array configuration located on top of an amorphous silicon substrate. Using the computational electromagnetics software Ansys HFSS, the electromagnetic energy absorption enhancement in the silicon layer is optimized by varying the geometric configuration. Percentage enhancement of the generated photocurrent is approximated and is used to compare the performance of various nanotoroid designs, as well as comparison to other geometries.

关键词： program unit solar cells Geometric forms Computational electromagnetics Electromagnetic Energies arrays Refractive surgery enhancement amorphous silicon

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Broadband absorptance high efficiency silicon nanowire fractal arrays for photovoltaic applications

Broadband absorptance high efficiency silicon nanowire fract...

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2014 MRS Spring Meeting

作者： Alzoubi, Omar H. Abu-Safe, Husam Alshurman, Khalid Naseem, Hameed A. Department of Electrical Engineering University of Arkansas FayettevilleAR72701 United States Natural Resources Engineering and Management German-Jordanian University Madaba Jordan Microelectronics and Photonics Program University of Arkansas FayettevilleAR72701 United States

Nanowire arrays have been proposed to enhance light trapping, increase efficiencies, and reduced material cost in photovoltaic solar cells. In this work we present a new crystalline silicon nanowire array structure, inspired by fractal geometry. The array structure is assumed to be an infinite 2D array in the x and y directions, and composed of vertically aligned SiNW suspended in air. Hexagonal fractal-like geometry is adapted in arranging cylindrical SiNW in these arrays. Full-wave finite element method 3D simulation is used to compute reflectance, transmittance and absorptance of the array for a normal incidence plane wave. The proposed fractal-like distribution of SiNW arrays yield broad absorption spectrum and enhanced efficiency while using less material. The efficiency of the proposed fractal-like SiNW arrays achieve ∼100% enhancement over that of the equivalent thickness flat c-Si film, and ∼18% enhancement over an equivalent height hexagonal array. The proposed optimized structures achieved a filling ratio ∼25%, which is ∼33% less than the corresponding hexagonal array. Copyright © 2014 Materials Research Society.

关键词： Silicon compounds

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A wafer-level packaging approach for MEMS & related microsystems using selective Laser-Assisted Bonding (LAB)

A wafer-level packaging approach for MEMS & related microsys...

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55th Electronic Components and Technology Conference, ECTC

作者： Mohan, Ashwin O'Neal, Chad B. Malshe, Ajay P. Foster, Ron B. Department of Mechanical Engineering University of Arkansas Fayetteville AR 72701 United States Institute for Micromanufacturing Louisiana Tech University Ruston LA 71272 United States Microelectronics-Photonics Program University of Arkanasas Fayetteville AR 72701 United States

A wafer-level bonding technique for hermetic, near-hermetic & vacuum packaging of MEMS is proposed. Silicon wafers are metallized with an intermediate layer of gold on which a low temperature solder such as Pb37/Sn63 having a thickness of 50-100 μm is deposited. The bonding layer is deposited either by screen printing or eutectic preforms. Two identical wafers are aligned at the intermediate layer and a continuous wave CO2 laser in combination with an X-Y translation stage is employed for selective heating of the silicon wafer to reflow the solder, bonding the wafers. The laser used had a wavelength of 10.6 μm with a spot size of 0.2-1.0 mm. The bonding temperature at the intermediate layer exceeded the reflow temperature of the eutectic Pb-Sn solder due to local laser heating effects, but the global average temperature was much lower (about 100°C). For a vacuum packaging approach the wafers were mounted on a custombuilt wafer-mating fixture housed in a vacuum chamber maintained at a pressure of 10-3 Torr. Optical, x-ray and acoustic microscopy were performed on the bonded wafer and pull tests on the diced packages to assess the quality of the solder bonds. © 2005 IEEE.

关键词： Electronics packaging

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Optical emission spectroscopy in a reactive ion etching system

Optical emission spectroscopy in a reactive ion etching syst...

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2007 IEEE Region 5 Technical Conference, TPS

作者： Koirala, S.P. Gordon, M.H. Cai, L. Burkett, S.L. Schaper, L.W. Microelectronics-Photonics Program University of Arkansas Fayetteville AR 72701 United States Department of Mechanical Engineering University of Arkansas Fayetteville AR 72701 United States Department of Electrical Engineering University of Arkansas Fayetteville AR 72701 United States

ISBN: (纸本)1424412803

In this work, we utilize optical emission spectroscopy (OES) to monitor the excited state densities of fluorine atoms in a 100 mTorr, 40 seem sulfur hexafluoride (SF6) plasma at both 100 and 250 W. Emission data were collected from 350nm to 1000nm through a quartz viewport using a 400 um optical fiber connected to an OceanOptics USB4000 CCD system with a 10m entrance slit. After obtaining the relative spectral response of our system using a tungsten halogen lamp, we generated fluorine excited state Boltzmann plots. Results indicate a 50 % increase in the fluorine excited state population for the 250W plasma compared to the 100W discharge, and, more surprisingly, a population inversion (higher population of the higher energy states);however, this latter result is consistent with other data in the literature. We suspect the cause for the population inversion is the low pressure, and thus low collision frequencies, in conjunction with an upper state metastable state. ©2007 IEEE.

关键词： Sulfur hexafluoride

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Fabrication and characterization of c-si solar cells integrated with ordered metallic nanostructure arrays

Fabrication and characterization of c-si solar cells integra...

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2012 38th IEEE Photovoltaic Specialists Conference

作者： Liang Huang Husam Hamza Abu-Safe Matthew Young Seth Shumate Benjamin Newton Hameed Naseem Shui-Qing Yu Department of Electrical Engineering Microelectronics-Photonics Program University of Arkansas Fayetteville AR USA Department of Electrical Engineering University of Arkansas Fayetteville AR USA Natural science division Lebanese American University Lebanon Microelectronics-Photonics Program University of Arkansas Fayetteville AR USA

In this study we present the fabrication process and characterization techniques to integrate metallic nanostructures on the surface of crystalline Si (c-Si) solar cells. These structures are designed to enhance light trapping at particular wavelengths [2]. Tuning the wavelength to maximize the efficiency can be achieved by changing the sizes and shapes of these structures. A special design of these structures atop c-Si solar cell is expected to affect the absorption near the band gap. These structures have been fabricated by electron beam lithography on c-Si substrates. The processing integration and preliminary characterization results of metallic nanostructures on c-Si solar cells are reported.

关键词： Photovoltaic cells Absorption Plasmons Silicon Gold Nanowires

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