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Displaying 26 - 50 of 82

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

In situ temperature measurements for selective epitaxy of GaN nanowires

February 17, 2014
Author(s)
Kristine A. Bertness, Matthew D. Brubaker, Todd E. Harvey, Shannon M. Duff, Aric W. Sanders, Norman A. Sanford
We demonstrate with spatially resolved, in situ temperature measurements and ex situ reflectance measurements that differences in appearance for masked and unmasked surfaces on patterned growth substrates arise from wavelength-dependent emissivity

Catalyst-free GaN Nanowires as Nanoscale Light Emitters

March 1, 2012
Author(s)
Kristine A. Bertness, Norman A. Sanford, John B. Schlager, Alexana Roshko, Todd E. Harvey, Paul T. Blanchard, Matthew D. Brubaker, Andrew M. Herrero, Aric W. Sanders
Catalyst-free growth of GaN nanowires with molecular beam epitaxy produces material of exceptionally high quality with long minority carrier lifetimes and low surface recombination velocity. The nanowires grow by thermodynamic driving forces that enhance

MOSFETs made from GaN nanowires with fully conformal cylindrical gates

December 2, 2011
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Aric W. Sanders, Norman A. Sanford, Steven M. George, Dragos Seghete
We report novel metal-oxide-semiconductor field effect transistors (MOSFETs) based on individual gallium nitride (GaN) nanowires with fully conformal cylindrical gates. The W/Al 2O 3 gates were deposited by atomic layer deposition. Reverse-bias breakdown

Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth growth on MBE nanowires

October 25, 2011
Author(s)
Aric Sanders, Paul T. Blanchard, Kristine A. Bertness, Matthew D. Brubaker, Ann Chiaramonti Debay, Christopher M. Dodson, Todd E. Harvey, Andrew M. Herrero, Devin M. Rourke, John B. Schlager, Norman Sanford, Albert Davydov, Abhishek Motayed, Denis Tsvetkov
We present the homoepitaxial growth of p-type, magnesium-doped gallium nitride shells using halide vapor phase epitaxy on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy. Scanning electron microscopy shows clear dopant

Controlled nucleation of GaN nanowires grown with molecular beam epitaxy

July 13, 2010
Author(s)
Kristine A. Bertness, Aric W. Sanders, Devin M. Rourke, Todd E. Harvey, Alexana Roshko, Norman A. Sanford
The location of GaN nanowires was controlled with essentially perfect selectivity using patterned SiNx prior to molecular beam epitaxy growth. Growth was uniform within mask openings and absent on the mask surface for over 95 % of the usable area of a 76

Lateral variations in self-assembled InGaAs quantum dot distributions

June 26, 2009
Author(s)
Alexana Roshko, Todd E. Harvey, Brittany L. Hyland, Lehman Y. Susan, Keith D. Cobry
The lateral uniformity of self-assembled InGaAs quantum dots grown by molecular beam epitaxy(MBE) was assessed as a function of growth conditions. Variations in the dot density and height were determined from atomic force micrographs. Growth rate had a

Topography of epitaxial GaAs surfaces for growth

April 30, 2009
Author(s)
Susan Y. Lehman, Alexana Roshko, Richard Mirin, Kristine A. Bertness, Todd E. Harvey, Keith D. Cobry
The topography and surface roughness of (100) GaAs substrates and buffers after different preparation procedures were determined from atomic force microscopy measurements. The influence of substrate aging and chemical etching on buffers grown by molecular

GaN nanowire carrier concentration calculated from light and dark resistance measurements

January 30, 2009
Author(s)
Lorelle Mansfield, Kristine A. Bertness, Paul T. Blanchard, Todd E. Harvey, Aric W. Sanders, Norman A. Sanford
We obtained limits on the carrier concentration and mobility of silicon-doped gallium nitride nanowires at room temperature with light and dark resistance data. Current-voltage measurements were performed on single-nanowire devices in the dark and under

MESFETs made from individual GaN nanowires

November 1, 2008
Author(s)
Paul T. Blanchard, Kristine A. Bertness, Todd E. Harvey, Lorelle Mansfield, Aric W. Sanders, Norman A. Sanford
In this paper, we demonstrate novelMESFETs based on individual GaN nanowires. The Pt/Au Schottky gates exhibited excellent two-terminal Schottky diode rectification behavior. The average effective Schottky barrier height was 0.87 eV, with an average

Designing high electron mobility transistor heterostructures with quantum dots for efficient, number-resolving photon detection

May 1, 2008
Author(s)
Mary A. Rowe, Eric Gansen, M. Greene, Danna Rosenberg, Todd E. Harvey, Mark Su, Robert Hadfield, Sae Woo Nam, Richard P. Mirin
We describe the design of the epitaxial layers for an efficient, photon-number-determining detector that utilizes a layer of self-assembled quantum dots as an optically addressable gate in a field-effect transistor. Our design features a dedicated

Mechanism for spontaneous growth of GaN nanowires with molecular beam epitaxy

April 1, 2008
Author(s)
Kristine A. Bertness, Alexana Roshko, Lorelle Mansfield, Todd E. Harvey, Norman A. Sanford
Although most semiconductor nanowires are grown via the vapor-liquid-solid mechanism, we present evidence that GaN nanowires form because of thermodynamically driven variations in surface sticking coefficients on different crystallographic planes under

Photon-number-discriminating detection using a quantum-dot, optically gated, field-effect transistor

October 1, 2007
Author(s)
Eric Gansen, Mary A. Rowe, M. Greene, Danna Rosenberg, Todd E. Harvey, Mark Su, Robert Hadfield, Sae Woo Nam, Richard Mirin
Detectors with the capability to directly measure the photon number of a pulse of light 1-3 enable linear optics quantum computing 4, affect the security of quantum communications 5, and can be used to characterize 6-8 and herald 9 non-classical states of

Nucleation and propagation mechanisms for catalyst-free growth of GaN nanowires

September 16, 2007
Author(s)
Kristine A. Bertness, Devin M. Rourke, Alexana Roshko, Lorelle Mansfield, Aric W. Sanders, Todd E. Harvey, Norman A. Sanford
Nucleation of GaN nanowires without catalysts in molecular beam epitaxy is shown to be a distinct process from nanowire propagation. Nanowire growth is relatively insensitive to starting conditions once the nanowire morphology is established, and is driven

Operational analysis of a quantum dot, optically gated, field-effect transistor as a single-photon detector

July 1, 2007
Author(s)
Eric Gansen, Mary A. Rowe, Marion Greene, Danna Rosenberg, Todd E. Harvey, Mark Su, Robert Hadfield, Sae Woo Nam, Richard Mirin
We report on the operation of a novel single-photon detector, where a layer of self-assembled quantum dots (QDs) is used as an optically addressable floating gate in a GaAs/Al0.2Ga0.8As Δ}-doped field-effect transistor. Photogenerated holes charge the QDs

Photon-number-resolving capabilities of a semiconductor quantum dot, optically gated, field-effect transistor

May 6, 2007
Author(s)
Eric Gansen, Mary A. Rowe, Marion Greene, Danna Rosenberg, Todd E. Harvey, Mark Su, Robert Hadfield, Sae Woo Nam, Richard Mirin
We demonstrate the photon-number-resolving capabilities of a novel quantum dot, optically gated, field-effect transistor cooled to 4 K. Peaks are observed in the detector's response to highly attenuated laser pulses in accordance with Poisson statistics.

Single-photon detection using a quantum dot optically gated field-effect transistor with high internal quantum efficiency

December 19, 2006
Author(s)
Mary A. Rowe, Eric Gansen, Marion Greene, Danna Rosenberg, Robert Hadfield, Todd E. Harvey, Sae Woo Nam, Mark Su, Richard Mirin
We investigate the operation of a quantum dot, optically gated, field-effect transistor as a photon detector. The detector exhibits time-gated, single-shot, single-photon sensitivity, a linear response, and an internal quantum efficiency of up to [68±18] %

Nucleation conditions for catalyst-free GaN nanowires

December 8, 2006
Author(s)
Kristine A. Bertness, Alexana Roshko, Lorelle Mansfield, Todd E. Harvey, Norman Sanford
We have examined the initial steps for catalyst-free growth of GaN using molecular beam epitaxy on Si (111) substrates using AlN buffer layers. These wires form spontaneously under high N-to-Ga ratios for a growth temperature range of about 810 to 830 °C

Composition Standards for AlGaAs Epitaxial Layers

April 1, 2006
Author(s)
Kristine A. Bertness, Todd E. Harvey, C. M. Wang, Albert J. Paul, Larry Robins
Standard Reference Materials (SRMs) 2840 to 2843 are semiconductor material artifacts that consist of an epitaxial layer of AlxGa (1-x)As on a GaAs substrate. From the energy at the peak intensity in the photoluminescence (PL) spectrum, the composition of

GaAs Buffer Layer Morphology and Lateral Distributions of InGaAs Quantum Dots

May 1, 2005
Author(s)
Alexana Roshko, Todd E. Harvey, Susan Y. Lehman, Richard Mirin, Kristine A. Bertness, Brittany Hyland
Atomic force microscopy was used to study the morphology of GaAs buffer layers and the density and height distributions of self-assembled InGaAs quantum dots (QDs) grown on these buffers by molecular beam epitaxy. The surface roughness and terrace size of

Cavity ring-down spectroscopy of semiconductor quantum dots

May 16, 2004
Author(s)
Joseph J. Berry, Todd E. Harvey, Richard Mirin, A Marian, Jun Ye
We employ cavity ringdown to perform absorption experiments of InGaAs/GaAs QDs. Integrating an AlAs/GaAs DBR incorporating InGaAs QD?s into a Fabry-Perot cavity, we demonstrate this approach and its potentials for sensitive measurements on semiconductor

Photoluminescence from an Nd3+ doped AlGaAs semiconductor structure

May 16, 2004
Author(s)
Kirk Ullmann, Mark Su, Kevin L. Silverman, Joseph J. Berry, Todd E. Harvey, Richard Mirin
We report room temperature photoluminescence from a Nd3+ doped AlGaAs semiconductor. Oxidation of the AlGaAs greatly improves the luminescence efficiency of the Nd3+ ions.

Composition Verification of AlGaAs Epitaxial Layers using Inductively Coupled Plasma Optical-Emission Spectroscopy

September 28, 2003
Author(s)
Kristine A. Bertness, Todd E. Harvey, Albert J. Paul, Larry Robins, Gregory C. Turk, Therese A. Butler, Marc L. Salit
We have applied an analytical chemistry method, inductively coupled plasma optical-emission spectroscopy (ICP-OES), to increase the accuracy of composition measurement of AlGaAs epitaxial thin films. ICP-OES results were compared with composition