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Spann BT, Weber JC, Brubaker MD, Harvey TE, Yang L, Honarvar H, Tsai CN, Treglia AC, Lee M, Hussein MI, Bertness KA. Semiconductor Thermal and Electrical Properties Decoupled by Localized Phonon Resonances. Adv Mater 2023:e2209779. [PMID: 36951229 DOI: 10.1002/adma.202209779] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2022] [Revised: 01/11/2023] [Indexed: 05/12/2023]
Abstract
Thermoelectric materials convert heat into electricity through thermally driven charge transport in solids or vice versa for cooling. To compete with conventional energy-conversion technologies, a thermoelectric material must possess the properties of both an electrical conductor and a thermal insulator. However, these properties are normally mutually exclusive because of the interconnection between scattering mechanisms for charge carriers and phonons. Recent theoretical investigations on sub-device scales have revealed that nanopillars attached to a membrane exhibit a multitude of local phonon resonances, spanning the full spectrum, that couple with the heat-carrying phonons in the membrane and cause a reduction in the in-plane thermal conductivity, with no expected change in the electrical properties because the nanopillars are outside the pathway of voltage generation and charge transport. Here this effect is demonstrated experimentally for the first time by investigating device-scale suspended silicon membranes with GaN nanopillars grown on the surface. The nanopillars cause up to 21% reduction in the thermal conductivity while the power factor remains unaffected, thus demonstrating an unprecedented decoupling in the semiconductor's thermoelectric properties. The measured thermal conductivity behavior for coalesced nanopillars and corresponding lattice-dynamics calculations provide evidence that the reductions are mechanistically tied to the phonon resonances. This finding paves the way for high-efficiency solid-state energy recovery and cooling.
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Affiliation(s)
- Bryan T Spann
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Boulder, CO, 80302, USA
| | - Joel C Weber
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Boulder, CO, 80302, USA
| | - Matt D Brubaker
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Boulder, CO, 80302, USA
| | - Todd E Harvey
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Boulder, CO, 80302, USA
| | - Lina Yang
- School of Aerospace Engineering, Beijing Institute of Technology, Beijing, 100081, China
| | - Hossein Honarvar
- Ann and H.J. Smead Department of Aerospace Engineering Sciences, University of Colorado Boulder, Boulder, CO, 80303, USA
| | - Chia-Nien Tsai
- Ann and H.J. Smead Department of Aerospace Engineering Sciences, University of Colorado Boulder, Boulder, CO, 80303, USA
| | - Andrew C Treglia
- Department of Physics, University of Colorado Boulder, Boulder, CO, 80302, USA
| | - Minhyea Lee
- Department of Physics, University of Colorado Boulder, Boulder, CO, 80302, USA
| | - Mahmoud I Hussein
- Ann and H.J. Smead Department of Aerospace Engineering Sciences, University of Colorado Boulder, Boulder, CO, 80303, USA
- Department of Physics, University of Colorado Boulder, Boulder, CO, 80302, USA
| | - Kris A Bertness
- Physical Measurement Laboratory, National Institute of Standards and Technology (NIST), Boulder, CO, 80302, USA
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Brubaker MD, Roshko A, Berweger S, Blanchard PT, Little CAE, Harvey TE, Sanford NA, Bertness KA. Crystallographic polarity measurements in two-terminal GaN nanowire devices by lateral piezoresponse force microscopy. Nanotechnology 2020; 31:424002. [PMID: 32580185 DOI: 10.1088/1361-6528/ab9fb2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
Lateral piezoresponse force microscopy (L-PFM) is demonstrated as a reliable method for determining the crystallographic polarity of individual, dispersed GaN nanowires that were functional components in electrical test structures. In contrast to PFM measurements of vertically oriented (as-grown) nanowires, where a biased probe tip couples to out-of-plane deformations through the d33 piezoelectic coefficient, the L-PFM measurements in this study were implemented on horizontally oriented nanowires that coupled to shear deformations through the d15 coefficient. L-PFM phase-polarity relationships were determined experimentally using a bulk m-plane GaN sample with a known [0001] direction and further indicated that the sign of the d15 piezoelectric coefficient was negative. L-PFM phase images successfully revealed the in-plane [0001] orientation of self-assembed GaN nanowires as part of a growth polarity study and results were validated against scanning transmission electron microscopy lattice images. Combined characterization of electrical properties and crystallographic polarity was also implemented for two-terminal GaN/Al0.1Ga0.9N/GaN nanowires devices, demonstrating L-PFM measurements as a viable tool for assessing correlations between device rectification and polarization-induced band bending.
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Affiliation(s)
- Matt D Brubaker
- Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO, United States of America
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Brubaker MD, Genter KL, Roshko A, Blanchard PT, Spann BT, Harvey TE, Bertness KA. UV LEDs based on p-i-n core-shell AlGaN/GaN nanowire heterostructures grown by N-polar selective area epitaxy. Nanotechnology 2019; 30:234001. [PMID: 30776789 PMCID: PMC7679058 DOI: 10.1088/1361-6528/ab07ed] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
Ultraviolet light-emitting diodes fabricated from N-polar AlGaN/GaN core-shell nanowires (NWs) with p-i-n structure produced electroluminescence at 365 nm with ∼5× higher intensities than similar GaN homojunction LEDs. The improved characteristics were attributed to localization of spontaneous recombination to the NW core, reduction of carrier overflow losses through the NW shell, and elimination of current shunting. Poisson-drift-diffusion modeling indicated that a shell Al mole fraction of x = 0.1 in Al x Ga1-x N effectively confines electrons and injected holes to the GaN core region. AlGaN overcoat layers targeting this approximate Al mole fraction were found to possess a low-Al-content tip and high-Al-content shell, as determined by scanning transmission electron microscopy. Photoluminescence spectroscopy further revealed the actual Al mole fraction to be NW diameter-dependent, where the tip and shell compositions converged towards the nominal flux ratio for large diameter NWs.
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Affiliation(s)
- Matt D Brubaker
- Physical Measurement Laboratory, National Institute of Standards and Technology, Boulder, CO, United States of America
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Roshko A, Brubaker MD, Blanchard PT, Harvey TE, Bertness KA. Eutectic Formation, V/III Ratio and Controlled Polarity Inversion in Nitrides on Silicon [1]. Phys Status Solidi B Basic Solid State Phys 2019; 257:10.1002/pssb.201900611. [PMID: 33335451 PMCID: PMC7739546 DOI: 10.1002/pssb.201900611] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Indexed: 06/12/2023]
Abstract
The crystallographic polarity of AlN grown on Si(111) by plasma assisted molecular beam epitaxy is intentionally inverted from N-polar to Al-polar at a planar boundary. The position of the inversion boundary is controlled by a two-step growth process that abruptly changes from Al-rich to N-rich growth conditions. The polarity inversion is induced by the presence of Si, which is incorporated from an Al-Si eutectic layer that forms during the initial stages of AlN growth and floats on the AlN surface under Al-rich growth conditions. When the growth conditions change to N-rich the Al and Si in the eutectic react with the additional N-flux and are incorporated into the solid AlN film. Relatively low levels of Al-Si eutectic formation combined with lateral variations in the Si incorporation lead to nonuniformity in the polarity inversion and formation of surprisingly narrow, vertical inversion domains. The results suggest that intentional incorporation of uniform layers of Si may provide a method for producing polarity engineered nitride structures.
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Affiliation(s)
- Alexana Roshko
- Physical Measurement Laboratory, National Institute of Standards and Technology 325 Broadway, Boulder, CO, 80305, USA
| | - Matt D Brubaker
- Physical Measurement Laboratory, National Institute of Standards and Technology 325 Broadway, Boulder, CO, 80305, USA
| | - Paul T Blanchard
- Physical Measurement Laboratory, National Institute of Standards and Technology 325 Broadway, Boulder, CO, 80305, USA
| | - Todd E Harvey
- Physical Measurement Laboratory, National Institute of Standards and Technology 325 Broadway, Boulder, CO, 80305, USA
| | - Kris A Bertness
- Physical Measurement Laboratory, National Institute of Standards and Technology 325 Broadway, Boulder, CO, 80305, USA
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Mingardi A, Zhang WD, Brown ER, Feldman AD, Harvey TE, Mirin RP. High power generation of THz from 1550-nm photoconductive emitters. Opt Express 2018; 26:14472-14478. [PMID: 29877484 DOI: 10.1364/oe.26.014472] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Accepted: 04/28/2018] [Indexed: 06/08/2023]
Abstract
Two photoconductive emitters - one with a self-complementary square spiral antenna, and the other with a resonant slot antenna - were fabricated on a GaAs epilayer embedded with ErAs quantum dots. Driven with 1550 nm mode-locked lasers, ~117 μW broadband THz power was generated from the device with the spiral antenna, and ~1.2 μW from the device with resonant slot antenna. The optical-to-THz conversion is through extrinsic photoconductivity.
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Brubaker MD, Genter KL, Weber JC, Spann BT, Roshko A, Blanchard PT, Harvey TE, Bertness KA. Core-shell p-i-n GaN nanowire LEDs by N-polar selective area growth. Proc SPIE Int Soc Opt Eng 2018; 10725. [PMID: 33343056 DOI: 10.1117/12.2322832] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
GaN nanowire LEDs with radial p-i-n junctions were grown by molecular beam epitaxy using N-polar selective area growth on Si(111) substrates. The N-polar selective area growth process facilitated the growth of isolated and high-aspect-ratio n-type NW cores that were not subject to self-shadowing effects during the subsequent growth of a conformal low-temperature Mg:GaN shell. LED devices were fabricated from single-NW and multiple-NW arrays in their as-grown configuration by contacting the n-type core through an underlying conductive GaN layer and the p-type NW shell via a metallization layer. The NW LEDs exhibited rectifying I-V characteristics with a sharp turn-on voltage near the GaN bandgap and low reverse bias leakage current. Under forward bias, the NW LEDs produced electroluminescence with a peak emission wavelength near 380 nm and exhibited a small spectral blueshift with increasing current injection, both of which are consistent with electron recombination in the p-type shell layer through donor-acceptor-pair recombination. These core-shell NW devices demonstrate N-polar selective area growth as an effective technique for producing on-chip nanoscale light sources.
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Affiliation(s)
- Matt D Brubaker
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Kristen L Genter
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305.,Department of Mechanical Engineering, University of Colorado, 1111 Engineering Drive, Boulder, CO USA 80309
| | - Joel C Weber
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Bryan T Spann
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Alexana Roshko
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Paul T Blanchard
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Todd E Harvey
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
| | - Kris A Bertness
- Physical Measurement Laboratory, National Institute of Standards and Technology, 325 Broadway, Boulder, CO, USA 80305
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Roshko A, Brubaker MD, Blanchard PT, Bertness KA, Harvey TE, Geiss RH, Levin I. Comparison of convergent beam electron diffraction and annular bright field atomic imaging for GaN polarity determination. J Mater Res 2017; 32:10.1557/jmr.2016.443. [PMID: 31274956 PMCID: PMC6604648 DOI: 10.1557/jmr.2016.443] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A comparison of two electron microscopy techniques used to determine the polarity of GaN nanowires is presented. The techniques are convergent beam electron diffraction (CBED) in TEM mode and annular bright field (ABF) imaging in aberration corrected STEM mode. Both measurements were made at nominally the same locations on a variety of GaN nanowires. In all cases the two techniques gave the same polarity result. An important aspect of the study was the calibration of the CBED pattern rotation relative to the TEM image. Three different microscopes were used for CBED measurements. For all three instruments there was a substantial rotation of the diffraction pattern (120 or 180°) relative to the image, which, if unaccounted for, would have resulted in incorrect polarity determination. The study also shows that structural defects such as inversion domains can be readily identified by ABF imaging, but may escape identification by CBED. The relative advantages of the two techniques are discussed.
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Affiliation(s)
| | | | | | | | | | - Roy H. Geiss
- Department of Chemistry, Colorado State University, Fort Collins, CO 80523
| | - Igor Levin
- Materials Measurement Science Division, NIST, Gaithersburg, MD 20899
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Ohlendorf HM, Marois KC, Lowe RW, Harvey TE, Kelly PR. Trace elements and organochlorines in surf scoters from San Francisco Bay, 1985. Environ Monit Assess 1991; 18:105-122. [PMID: 24233749 DOI: 10.1007/bf00394973] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/15/1989] [Indexed: 06/02/2023]
Abstract
Surf scoters (Melanitta perspicillata) were collected from 6 locations in San Francisco Bay during January and March 1985. Overall, mean concentrations of cadmium and zinc were higher in livers of scoters from the southern region of the Bay, whereas mean iron and lead were higher in those from the northern Bay region. Mean concentrations of arsenic, copper, lead, zinc, aluminum (January only) and iron (January) also differed among individual locations. Mean concentrations of copper and zinc increased, arsenic decreased, and cadmium remained the same between January and March. Selenium and mercury concentrations in scoter livers were not significantly correlated (P>0.05), but cadmium concentrations in livers and kidneys were positively correlated (P<0.0001), and body weight was negatively related to mercury concentration in the liver (P<0.05). Body weight differed among locations but not between January and March. Body weight was correlated with lipid content (P<0.0001). DDE and PCBs were each detected in 34 of 36 scoter carcasses. DDE increased significantly between January and March at Richmond Harbor, but BCBs did not differ between January and March at the 3 locations that could be tested.
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Affiliation(s)
- H M Ohlendorf
- U.S. Fish and Wildlife Service, Patuxent Wildlife Research Center, Pacific Coast Research Station, USA
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Harvey TE. The Donald Munro memorial lecture. J Am Paraplegia Soc 1988; 11:3-5. [PMID: 3288714] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
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Abstract
Tritiated 4-androstene-3,17-dione and testosterone were incubated with submaxillary gland homogenates of male and female rats. The metabolism was predominately reductive. In 15 and 180 min incubations submaxillary tissue converted 4-androstene-3,17-dione chiefly to androsterone. Less testosterone, 17 beta-hydroxy-5 alpha-androstan-3-one, 5 alpha-androstane-3,17-dione, 5 alpha-androstane-3 alpha, 17 beta-diol, and 4-androstene-3 alpha, 17 beta-diol were also identified. Testosterone was converted to the same products plus 4-androstene-3,17-dione. 5 alpha-Androstane-3 alpha, 17 beta-diol was the major testosterone metabolite. Qualitatively the metabolism by male and female submaxillary gland was similar.
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