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Search Publications by: Norman A. Sanford (Fed)

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Displaying 76 - 100 of 161

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

Application of Microwave Scanning Probes to Photovoltaic Materials

June 20, 2010
Author(s)
Kristine A. Bertness, John B. Schlager, Norman A. Sanford, Atif A. Imtiaz, Thomas M. Wallis, Joel C. Weber, Pavel Kabos, Lorelle M. Mansfield
We demonstrate that near field scanning microwave microscopy (NSMM) can be used to detect photoresponse in photovoltaic materials with potential for submicrometer resolution. In this approach, a radio-frequency scanning tunneling microscopy (RF-STM) tip is

High frequency characterization of a Schottky contact to a GaN nanowire bundle

June 16, 2010
Author(s)
Chin J. Chiang, Thomas M. Wallis, Dazhen Gu, Atif A. Imtiaz, Pavel Kabos, Paul T. Blanchard, Kristine A. Bertness, Norman A. Sanford, Kichul Kim, Dejan Filipovic
A GaN nanowire (NW) Schottky contact was characterized up to 10 GHz. Using a calibration procedure and circuit model a capacitance-voltage (CV) curve was obtained, from which a carrier concentration was calculated for the first time. These results

Steady-state and transient photoconductivity in c-axis GaN nanowires grown by nitrogen-plasma-assisted molecular beam epitaxy

February 12, 2010
Author(s)
Norman A. Sanford, Paul T. Blanchard, Kristine A. Bertness, Lorelle Mansfield, John B. Schlager, Aric W. Sanders, Alexana Roshko, Beau Burton, Steven George
Analysis of steady-state and transient photoconductivity measurements at room temperature performed on c-axis oriented GaN nanowires yielded estimates of free carrier concentration, drift, mobility, surface band bending, and surface capture coefficient for

Atomic layer deposition enabled interconnect technology for vertical nanowire array devices

June 20, 2009
Author(s)
Myongjai Lee, Jen-Hau Cheng, Kristine A. Bertness, Norman Sanford, Dragos Seghete, Steven M. George, Y.C. Lee
We have demonstrated an atomic layer deposition (ALD) enabled interconnect technology for vertical, c-axis oriented gallium nitride (GaN) nanowire (NW, 5-10m in length, 80-200nm in diameter) arrays encapsulated by benzocyclobutene (BCB). The nano-scaled

Packaging and interconnect technologies for GaN nanowire-based light emitting diodes

May 26, 2009
Author(s)
Norman A. Sanford, Myongjai Lee, Jen-Hau Cheng, Dragos Seghete, Steven M. George, John B. Schlager, Kristine A. Bertness
GaN nanowires grown along c-axis on a silicon substrate using molecular beam epitaxy have been identified as one of the best materials for future light emitting diodes (LEDs). These defectfree nanowires-based LEDs may reach the highest possible efficiency

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

Resistivity study of si-doped GaN nanowires grown by catalyst-free MBE

September 16, 2008
Author(s)
Lorelle Mansfield, Paul T. Blanchard, Devin M. Rourke, Aric W. Sanders, Norman A. Sanford, Kristine A. Bertness
GaN nanowires doped with silicon were grown on Si(111) substrates by catalyst-free molecular beam epitaxy (MBE). Contacts were fabricated to single nanowires with a Ti/Al metallization scheme. Low-resistance ohmic contacts were achieved after annealing for

Steady-state and time-resolved photoluminescence from relaxed and strained GaN nanowires grown by catalyst-free molecular-beam epitaxy

June 24, 2008
Author(s)
John B. Schlager, Kristine A. Bertness, Paul T. Blanchard, Lawrence H. Robins, Alexana Roshko, Norman A. Sanford
We report steady-state and time-resolved photoluminescence (TRPL) measurements on individual GaN nanowires (6-20 micrometers in length, 30-940 nm in diameter) grown by nitrogen-plasma-assisted, catalyst-free MBE on Si(111) and dispersed onto fused quartz

Calibrated Broadband Electrical Characterization of Nanowires

June 8, 2008
Author(s)
Thomas Mitchell (Mitch) Wallis, Atif A. Imtiaz, Hans Nembach, Kristine A. Bertness, Norman Sanford, Paul T. Blanchard, Pavel Kabos
A technique is presented for the broadband electrical characterization of nanowires. The technique relies on established on-wafer calibration methods as well as a direct measurement of the capacitive coupling that is in parallel with the nanowire

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

High-Q GaN nanowire resonators and oscillators

November 16, 2007
Author(s)
Shawn M. Tanner, Jason M. Gray, Charles T. Rogers, Kristine A. Bertness, Norman Sanford
We report high mechanical quality factors Q for GaN nanowire cantilevers grown by molecular beam epitaxy. Nanowires with 30-500 nm diameters and 5-20 υm lengths having resonance frequencies from 400 kHz to 2.8 MHz were measured. Q near room temperature and

Nanowire placement with ink jet heads

September 16, 2007
Author(s)
Kristine A. Bertness, Christopher M. Dodson, Paul T. Blanchard, Norman Sanford, Ross N. Mills
We show that thermal ink jet printheads can be used to place GaN nanowires on patterned substrates. The semiconductor nanowires have diameters ranging from 70 to 300 nm and lengths from 5 υm to 20 υm. They were dispersed in alcohol-water solutions for

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

Persistent photoconductivity studies of c-axis GaN nanowires grown by MBE

September 16, 2007
Author(s)
Norman Sanford, Paul T. Blanchard, Kristine A. Bertness, Alexana Roshko, Beau Burton, Lorelle Mansfield, John B. Schlager, Steven George, Aric Sanders
Photoconductivity (PC) and persistent photoconductivity (PPC) were measured on c-axis GaN nanowires (NWs) grown by catalyst-free nitrogen plasma assisted MBE on Si(111) substrates. Unintentionally doped n-type NWs from two separate growth batches were

Time-resolved photoluminescence study of GaN nanowires grown by catalyst-free MBE

September 16, 2007
Author(s)
John B. Schlager, Kristine A. Bertness, Paul T. Blanchard, Norman A. Sanford
We report steady-state and time-resolved photoluminescence (PL & TRPL) measurements on individual GaN nanowires that were grown by nitrogen-plasma-assisted, molecular beam epitaxy on Si(111) and subsequently dispersed onto fused quartz substrates for

Optical and structural study of GaN nanowires grown by catalyst-free molecular beam epitaxy. II. Sub-band-gap luminescence and electron irradiation effects

June 4, 2007
Author(s)
Larry Robins, Kristine A. Bertness, Joy Barker, Norman Sanford, John B. Schlager
GaN nanowires with diameters of 50-250nm, grown by catalyst-free molecular beam epitaxy, were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 to 297 K. Both as-grown samples and dispersions of

Optical and Structural Study of GaN Nanowires Grown by Catalyst-Free MBE: (II) Defect-Related Luminescence and Electron-Beam Irradiation Effects

June 1, 2007
Author(s)
Lawrence H. Robins, Kristine A. Bertness, John G. Barker, Norman A. Sanford, John B. Schlager
GaN nanowires grown by catalyst free molecular beam epitaxy were characterized by photoluminescence (PL) and cathodoluminescence (CL) spectroscopy at temperatures from 3 K to 295 K. Both as grown samples, which contained approximately vertically oriented

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