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Publications

Search Publications by

Matthew Brubaker (Fed)

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Displaying 1 - 25 of 37

AlGaN/GaN core-shell heterostructures for nanowire UV LEDs

May 1, 2020
Author(s)
Matthew D. Brubaker, Bryan T. Spann, Kristen L. Genter, Alexana Roshko, Paul T. Blanchard, Todd E. Harvey, Kristine A. Bertness
Nanowire-based ultraviolet (UV) LEDs hold great promise as nanoscale light sources, potentially enabling advanced scanning microscopy probes capable of optoelectronic sensing and near-field scanning photolithography. In this work, we report on the

Eutectic Formation, V/III Ratio and Controlled Polarity Inversion in Nitrides on Silicon

November 19, 2019
Author(s)
Alexana Roshko, Matthew D. Brubaker, Paul T. Blanchard, Todd E. Harvey, Kristine A. Bertness
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

The role of Si in GaN/AlN/Si(111) PAMBE Epitaxy: Polarity and Inversion

May 22, 2019
Author(s)
Alexana Roshko, Matthew D. Brubaker, Paul T. Blanchard, Todd E. Harvey, Kristine A. Bertness
The microstructure, polarity and Si distribution in AlN/GaN layers grown by PAMBE on Si(111) was assessed by STEM. Samples grown under both metal- and nitrogen-rich conditions contained defects at the AlN/Si interface which suggest formation of an Al-Si

UV LEDs Based on p-i-n Core-Shell AlGaN/GaN Nanowire Heterostructures Grown by N-polar Selective Area Epitaxy

March 21, 2019
Author(s)
Matthew D. Brubaker, Kristen L. Genter, Alexana Roshko, Paul T. Blanchard, Bryan T. Spann, Todd E. Harvey, Kristine A. Bertness
Ultraviolet light-emitting diodes (UV LEDs) fabricated from N-polar AlGaN/GaN core-shell nanowires with p-i-n structure produced electroluminescence at 365 nm with ~5x higher intensities than similar GaN homojunction LEDs. The improved characteristics were

Axisymmetric scalable magneto-gravitational trap for diamagnetic particle levitation

December 11, 2018
Author(s)
Kristine A. Bertness, John P. Houlton, Max L. Chen, Matthew D. Brubaker, Charles T. Rogers
We report an axisymmetric magnetic trap design for levitating diamagnetic particles. The magnetic traps each consist of two iron pole pieces passively driven by a neodymium iron boron (NdFeB) permanent magnet. The magnetic field configuration between the

An optical Bragg scattering readout for simultaneous detection of all low-order mechanical modes of gallium nitride nanowires in nanowire arrays

September 19, 2018
Author(s)
Kristine A. Bertness, John P. Houlton, Matthew D. Brubaker, Charles T. Rogers
We report the use of optical Bragg scattering and homodyne interferometry to simultaneously measure all the first order cantilever-mode mechanical resonance frequencies and quality factors (Q) of gallium nitride nanowires (GaN NWs) in 100 NW periodic

Core-Shell p-i-n GaN Nanowire LEDs by N-polar Selective Area Growth

September 11, 2018
Author(s)
Matthew D. Brubaker, Kristen L. Genter, Bryan T. Spann, Alexana Roshko, Paul T. Blanchard, Todd E. Harvey, Kristine A. Bertness
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

Raman spectroscopy for dopant optimization in GaN nanowire light-emitting diodes

May 1, 2018
Author(s)
Kristine A. Bertness, Bryan T. Spann, Matthew D. Brubaker, Todd E. Harvey, Paul T. Blanchard
We apply Raman spectroscopy to optimize both n-type and p-type doping in GaN nanowire light- emitting diodes (LEDs) grown with selective epitaxy on Si(111) with molecular beam epitaxy. N-type doping with Si is characterized using the peak shift in the LO

Spectral tuning of localized surface phonon-polariton modes in selective area epitaxy GaN nanowire arrays

May 1, 2018
Author(s)
Bryan T. Spann, J. Ryan Nolen, Matthew D. Brubaker, Thomas G. Folland, Chase T. Ellis, Joseph G. Tischler, Todd E. Harvey, Joshua D. Caldwell, Kristine A. Bertness
Polar semiconductor materials, such as GaN, InP, SiC et al., offer a basis to manufacture innovative long-wavelength photonic devices.1 Such semiconductors can support propagating and localized surface phonon-polariton (SPhP) resonances that provide highly

GaN Nanowire MOSFET with Near-Ideal Subthreshold Slope

December 21, 2017
Author(s)
Kristine A. Bertness, Wenjun Li, Matthew D. Brubaker, Bryan T. Spann, Patrick Fay
Top-gated GaN nanowire MOSFETs using Al2O3 as gate oxide have been experimentally demonstrated. The fabricated devices exhibit a minimum subthreshold slope of 60 mV/dec, an average subthreshold slope of 68 mV/dec over three decades of drain current, drain

Lithographic sonication patterning of large area nanopillar forests

July 27, 2017
Author(s)
Joel C. Weber, Matthew D. Brubaker, Thomas M. Wallis, Kristine A. Bertness
This paper demonstrates a highly-scalable, material-independent method for patterning nanopillar forests known as lithographic sonication patterning. Through contact lithography, patterns with dimensions down to 3 υm were written across a 3-inch silicon

Comparison of CBED and ABF Atomic Imaging for GaN Polarity Determination

November 8, 2016
Author(s)
Alexana Roshko, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Igor Levin, R.H. Geiss
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

Spontaneous growth of GaN nanowire nuclei on N- and Al-polar AlN: A piezoresponse force microscopy study of crystallographic polarity

March 2, 2016
Author(s)
Matthew D. Brubaker, Alexana Roshko, Paul T. Blanchard, Todd E. Harvey, Norman A. Sanford, Kristine A. Bertness
The polarity of gallium nitride (GaN) nanowire nuclei grown on AlN layers was studied by piezoresponse force microscopy (PFM). N- or Al-polar AlN layers were grown by molecular beam epitaxy (MBE) on Si (111) substrates by use of Al- or N-rich growth

Near-field control and imaging of free charge carrier variations in GaN nanowires

February 15, 2016
Author(s)
Samuel Berweger, Paul T. Blanchard, Matthew D. Brubaker, Kevin J. Coakley, Norman A. Sanford, Thomas M. Wallis, Kristine A. Bertness, Pavel Kabos
Despite their uniform crystallinity, the shape and faceting of semiconducting nanowires (NWs) can give rise to variations in structure and associated electronic properties. Here we investigate local variations in electronic structure across individual n

Polarity-Controlled GaN/AlN Nucleation Layers for Selective-Area Growth of GaN Nanowire Arrays on Si(111) Substrates by Molecular Beam Epitaxy

December 18, 2015
Author(s)
Matthew D. Brubaker, Shannon M. Duff, Todd E. Harvey, Paul T. Blanchard, Alexana Roshko, Aric W. Sanders, Norman A. Sanford, Kristine A. Bertness
We have demonstrated dramatic improvement in the quality of selective-area GaN nanowire growth by controlling the polarity of the underlying nucleation layers. In particular, we find that N- polarity is beneficial for the growth of large ordered nanowire

Selective Area Growth of Ga- and N-polar GaN Nanowire Arrays on Non-Polar Si (111) Substrates

September 7, 2014
Author(s)
Matthew D. Brubaker, Shannon M. Duff, Todd E. Harvey, Paul T. Blanchard, Alexana Roshko, Aric W. Sanders, Norman A. Sanford
This study presents a technique for obtaining Ga- and N-polar Gallium Nitride nanowire (GaN NW) arrays on non-polar Si (111) substrates by use of polarity-controlled AlN/GaN buffer layers. AlN films are demonstrated to adopt Al-/N-polarity for N-/Al-rich

Imaging the p-n junction in a gallium nitride nanowire with a scanning microwave microscope

July 2, 2014
Author(s)
Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Kevin J. Coakley, Matthew D. Brubaker, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford
We used a broadband, atomic-force-microscope-based, scanning microwave microscope (AFM-SMM) to probe the axial dependence of the depletion in a GaN nanowire (NW) p-n junction structure. The NWs were c-axis oriented and grown by molecular beam epitaxy. The

Influence of morphology on current-voltage behavior of GaN nanowires

July 1, 2014
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Matthew D. Brubaker, Todd E. Harvey, Aric W. Sanders, Norman A. Sanford
We demonstrate the effect that the different morphologies of MBE-grown GaN nanowires (NWs) can have upon current-voltage (I-V) behavior. Two main aspects of NW morphology were investigated. The first aspect was the NW diameter, dNW. For single-crystal Si

Characterization of InGaN quantum disks in GaN nanowires

March 4, 2014
Author(s)
Alexana Roshko, Roy H. Geiss, John B. Schlager, Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Todd E. Harvey
Catalyst-free GaN nanowires with InGaN quantum disks (QDs) were characterized by scanning/transmission elec-tron microscopy (S/TEM) and photoluminescence. A va-riety of structures, from QDs with large strain fields to apparently strain free QDs were

Characterization of InGaN quantum disks in GaN nanowires

February 27, 2014
Author(s)
Alexana Roshko, Roy H. Geiss, John B. Schlager, Matthew D. Brubaker, Kristine A. Bertness, Norman A. Sanford, Todd E. Harvey
Catalyst-free GaN nanowires with InGaN quantum disks (QDs) were characterized by scanning/transmission electron microscopy (S/TEM) and photoluminescence. A variety of structures, from QDs with large strain fields to apparently strain free QDs were observed