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Displaying 1 - 25 of 82

Semiconductor thermal and electrical properties decoupled by localized phonon resonances

May 10, 2023
Author(s)
Bryan Spann, Joel Weber, Matthew Brubaker, Todd E. Harvey, LINA YANG, Hossein Honarvar, Chia-Nien Tsai, Andrew Treglia, MINHYEA LEE, MAHMOUD HUSSEIN, Kris A. Bertness
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

Crystallographic Polarity Measurements in Two-Terminal GaN Nanowire Devices by Lateral Piezoresponse Force Microscopy

July 23, 2020
Author(s)
Matthew Brubaker, Alexana Roshko, Samuel Berweger, Paul T. Blanchard, Todd E. Harvey, Norman A. Sanford, Kris A. Bertness
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

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 20, 2019
Author(s)
Matthew Brubaker, Kristen Genter, Alexana Roshko, Paul T. Blanchard, Bryan T. Spann, Todd E. Harvey, Kris 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

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

Abrupt dependence of ultrafast extrinsic photoconductivity on er fraction in gaas:er

July 1, 2017
Author(s)
Elliott Brown, A. Mingardi, W-D. Zhang, Ari Feldman, Todd E. Harvey, Richard Mirin
We present a study of room-temperature, ultrafast photoconductivity associated with strong, sub-bandgap, resonant absorption around lamba} = 1550 nm in three MBE-grown GaAs epitaxial layers heavily doped with Er at concentrations of ≅2.9 x 10 18 (control

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

Ultra-low-noise monolithic mode-locked solid-state laser

September 1, 2016
Author(s)
T D. Shoji, W Xie, Kevin L. Silverman, Ari Feldman, Todd E. Harvey, Richard Mirin, Thomas Schibli
Low-noise, high-repetition-rate mode-locked solid-state lasers are attractive for precision measurement and microwave generation, but the best lasers in terms of noise performance still consist of complex, bulky optical setups, which limits their range of

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

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

Monolithic device for modelocking and stabilization of a frequency comb

December 15, 2015
Author(s)
Kevin L. Silverman, Richard P. Mirin, Ari D. Feldman, Todd E. Harvey, Thomas Schibli, Chien-Chung Lee, Yosuke Hayashi
We demonstrate a device that integrates a III-V semiconductor saturable absorber mirror with a graphene electro-optic modulator, which provides a monolithic solution to modelocking and noise suppression in a frequency comb. The device offers a pure loss

Electronic Enhancement of the Exciton Coherence Time in Charged Quantum Dots

October 19, 2015
Author(s)
Galan A. Moody, Corey A. McDonald, Ari D. Feldman, Todd E. Harvey, Richard P. Mirin, Kevin L. Silverman
Minimizing decoherence due to coupling of a quantum system to its fluctuating environment is at the forefront of quantum information and photonics research. Nature sets the ultimate limit, however, given by the strength of the system’s coupling to the

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

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

Establishing an upper bound on contact resistivity of ohmic contacts to n-GaN nanowires

April 1, 2014
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Norman A. Sanford
Contact resistivity ρ c is an important figure of merit in evaluating and improving the performance of electronic and optoelectronic devices. Due to the small size, unique morphology, and uncertain transport properties of semiconductor nanowires (NWs)

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