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Kazanowska BA, Sapkota KR, Lu P, Talin AA, Bussmann E, Ohta T, Gunning BP, Jones KS, Wang GT. Fabrication and field emission properties of vertical, tapered GaN nanowires etched via phosphoric acid. Nanotechnology 2021; 33:035301. [PMID: 34555820 DOI: 10.1088/1361-6528/ac2981] [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] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2021] [Accepted: 09/21/2021] [Indexed: 06/13/2023]
Abstract
The controlled fabrication of vertical, tapered, and high-aspect ratio GaN nanowires via a two-step top-down process consisting of an inductively coupled plasma reactive ion etch followed by a hot, 85% H3PO4crystallographic wet etch is explored. The vertical nanowires are oriented in the[0001]direction and are bound by sidewalls comprising of{336¯2}semipolar planes which are at a 12° angle from the [0001] axis. High temperature H3PO4etching between 60 °C and 95 °C result in smooth semipolar faceting with no visible micro-faceting, whereas a 50 °C etch reveals a micro-faceted etch evolution. High-angle annular dark-field scanning transmission electron microscopy imaging confirms nanowire tip dimensions down to 8-12 nanometers. The activation energy associated with the etch process is 0.90 ± 0.09 eV, which is consistent with a reaction-rate limited dissolution process. The exposure of the{336¯2}type planes is consistent with etching barrier index calculations. The field emission properties of the nanowires were investigated via a nanoprobe in a scanning electron microscope as well as by a vacuum field emission electron microscope. The measurements show a gap size dependent turn-on voltage, with a maximum current of 33 nA and turn-on field of 1.92 V nm-1for a 50 nm gap, and uniform emission across the array.
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Affiliation(s)
- Barbara A Kazanowska
- University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611, United States of America
| | - Keshab R Sapkota
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
| | - Ping Lu
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
| | - A Alec Talin
- Sandia National Laboratories, Livermore, CA 94550, United States of America
| | - Ezra Bussmann
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
| | - Taisuke Ohta
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
| | - Brendan P Gunning
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
| | - Kevin S Jones
- University of Florida, Department of Materials Science and Engineering, Gainesville, FL 32611, United States of America
| | - George T Wang
- Sandia National Laboratories, Albuquerque, NM 87185, United States of America
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Turner EM, Campbell Q, Pizarro J, Yang H, Sapkota KR, Lu P, Baczewski AD, Wang GT, Jones KS. Controlled Formation of Stacked Si Quantum Dots in Vertical SiGe Nanowires. Nano Lett 2021; 21:7905-7912. [PMID: 34582219 DOI: 10.1021/acs.nanolett.1c01670] [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] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We demonstrate the ability to fabricate vertically stacked Si quantum dots (QDs) within SiGe nanowires with QD diameters down to 2 nm. These QDs are formed during high-temperature dry oxidation of Si/SiGe heterostructure pillars, during which Ge diffuses along the pillars' sidewalls and encapsulates the Si layers. Continued oxidation results in QDs with sizes dependent on oxidation time. The formation of a Ge-rich shell that encapsulates the Si QDs is observed, a configuration which is confirmed to be thermodynamically favorable with molecular dynamics and density functional theory. The type-II band alignment of the Si dot/SiGe pillar suggests that charge trapping on the Si QDs is possible, and electron energy loss spectra show that a conduction band offset of at least 200 meV is maintained for even the smallest Si QDs. Our approach is compatible with current Si-based manufacturing processes, offering a new avenue for realizing Si QD devices.
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Affiliation(s)
- Emily M Turner
- Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Quinn Campbell
- Quantum Computer Science Department, Sandia National Laboratories, Albuquerque, New Mexico 87158, United States
| | - Joaquín Pizarro
- Department of Computer Engineering, University of Cádiz, Puerto Real 11519, Spain
| | - Hongbin Yang
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854, United States
| | - Keshab R Sapkota
- Advanced Materials Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico 87158, United States
| | - Ping Lu
- Department of Materials Characterization and Performance, Sandia National Laboratories, Albuquerque, New Mexico 87158, United States
| | - Andrew D Baczewski
- Quantum Computer Science Department, Sandia National Laboratories, Albuquerque, New Mexico 87158, United States
| | - George T Wang
- Advanced Materials Sciences Department, Sandia National Laboratories, Albuquerque, New Mexico 87158, United States
| | - Kevin S Jones
- Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States
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Abstract
The III-nitride semiconductors have many attractive properties for field-emission vacuum electronics, including high thermal and chemical stability, low electron affinity, and high breakdown fields. Here, we report top-down fabricated gallium nitride (GaN)-based nanoscale vacuum electron diodes operable in air, with record ultralow turn-on voltages down to ∼0.24 V and stable high field-emission currents, tested up to several microamps for single-emitter devices. We leverage a scalable, top-down GaN nanofabrication method leading to damage-free and smooth surfaces. Gap-dependent and pressure-dependent studies provide new insights into the design of future, integrated nanogap vacuum electron devices. The results show promise for a new class of high-performance and robust, on-chip, III-nitride-based vacuum nanoelectronics operable in air or reduced vacuum.
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Affiliation(s)
- Keshab R Sapkota
- Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - François Leonard
- Sandia National Laboratories, Livermore, California 94551, United States
| | - A Alec Talin
- Sandia National Laboratories, Livermore, California 94551, United States
| | - Brendan P Gunning
- Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
| | - Barbara A Kazanowska
- Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Kevin S Jones
- Department of Materials Science and Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - George T Wang
- Sandia National Laboratories, Albuquerque, New Mexico 87185, United States
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Sapkota KR, Chen W, Maloney FS, Poudyal U, Wang W. Magnetoresistance manipulation and sign reversal in Mn-doped ZnO nanowires. Sci Rep 2016; 6:35036. [PMID: 27739442 PMCID: PMC5064367 DOI: 10.1038/srep35036] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2016] [Accepted: 09/23/2016] [Indexed: 11/22/2022] Open
Abstract
We report magnetoresistance (MR) manipulation and sign reversal induced by carrier concentration modulation in Mn-doped ZnO nanowires. At low temperatures positive magnetoresistance was initially observed. When the carrier concentration was increased through the application of a gate voltage, the magnetoresistance also increased and reached a maximum value. However, further increasing the carrier concentration caused the MR to decrease, and eventually an MR sign reversal from positive to negative was observed. An MR change from a maximum positive value of 25% to a minimum negative value of 7% was observed at 5 K and 50 KOe. The observed MR behavior was modeled by considering combined effects of quantum correction to carrier conductivity and bound magnetic polarons. This work could provide important insights into the mechanisms that govern magnetotransport in dilute magnetic oxides, and it also demonstrated an effective approach to manipulating magnetoresistance in these materials that have important spintronic applications.
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Affiliation(s)
- Keshab R. Sapkota
- Department of Physics and Astronomy, University of Wyoming, Laramie WY, USA
| | - Weimin Chen
- Department of Physics and Astronomy, University of Wyoming, Laramie WY, USA
| | - F. Scott Maloney
- Department of Physics and Astronomy, University of Wyoming, Laramie WY, USA
| | - Uma Poudyal
- Department of Physics and Astronomy, University of Wyoming, Laramie WY, USA
| | - Wenyong Wang
- Department of Physics and Astronomy, University of Wyoming, Laramie WY, USA
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