J. M. Barker

Sandia National Laboratories

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D. K. Ferry

Arizona State University

Norman A. Sanford

National Institute of Standards and Technology

Alexana Roshko

National Institute of Standards and Technology

R. J. Shul

Sandia National Laboratories

John B. Schlager

National Institute of Standards and Technology

Kris A. Bertness

National Institute of Standards and Technology

Andrew A. Allerman

Sandia National Laboratories

Lawrence H. Robins

Brigham Young University

Stephen M. Goodnick

Arizona State University

Daniel Koleske

Sandia National Laboratories

Cooperative Institutions

National Institute of Standards and Technology

Sandia National Laboratories

Arizona State University

Sandia National Laboratories California

National Institute of Standards

Physical Measurement Laboratory

University of Colorado Boulder

Office of Scientific and Technical Information

United States Department of Commerce

National Technical Information Service

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Catalyst-free growth of GaN nanowires

Journal of Electronic Materials (2006)

Kris A. Bertness Norman A. Sanford J. M. Barker John B. Schlager Alexana Roshko

Solid-state physics

10.1007/s11664-006-0102-4

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Citations (100)

Bulk GaN and AlGaN∕GaN heterostructure drift velocity measurements and comparison to theoretical models

Journal of Applied Physics (2005)

J. M. Barker D. K. Ferry Daniel Koleske R. J. Shul

The room-temperature velocity-field characteristics for n-type gallium nitride and AlGaN∕GaN heterostructures, grown epitaxially on sapphire, were determined experimentally. A pulsed voltage input and four-point measurements were used on special geometry samples to determine the electron drift velocity as a function of applied electric field in the basal plane. These measurements show apparent saturation velocities near 2.5×107cm∕s at 180kV∕cm for the n-type gallium nitride and 3.1×107cm∕s at 140kV∕cm for the AlGaN∕GaN heterostructures. A comparison of these studies shows that the experimental velocities are close to previously published simulations based upon Monte Carlo techniques.

Wide-bandgap semiconductor

Saturation velocity

Velocity saturation

10.1063/1.1854724

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Citations (89)

Picosecond Raman Studies of Electron and Hole Velocity Overshoots In a GaAs-based p-i-n Semiconductor Nanostructure

AIP conference proceedings (2005)

W. Liang Kong‐Thon Tsen C. D. Poweleit J. M. Barker D. K. Ferry

Picosecond Raman spectroscopy has been employed to study electron and hole transport in a GaAs‐based p‐i‐n nanostructure. Electron as well hole velocity overshoots are observed. It has been demonstrated that due to the relatively long laser pulse used in the experiments the extent of overshoot is about the same in both cases.

Picosecond

Semiconductor nanostructures

Overshoot (microwave communication)

10.1063/1.1994571

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

Journal of Applied Physics (2007)

Lawrence H. Robins Kris A. Bertness J. M. Barker Norman A. Sanford John B. Schlager

GaN nanowires with diameters of 50–250 nm, 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 the nanowires onto other substrates were examined. The properties of the near-band-edge PL and CL spectra were discussed in Part I of this study by [Robins et al. [L. H. Robins, K. A. Bertness, J. M. Barker, N. A. Sanford, and J. B. Schlager, J. Appl. Phys. 101,113505 (2007)]. Spectral features below the band gap, and the effect of extended electron irradiation on the CL, are discussed in Part II. The observed sub-band-gap PL and CL peaks are identified as phonon replicas of the free-exciton transitions, or excitons bound to structural defects or surface states. The defect-related peaks in the nanowires are correlated with luminescence lines previously reported in GaN films, denoted the Y lines [M. A. Reshchikov and H. Morkoc, J. Appl. Phys. 97, 061301 (2005)]. The CL was partially quenched by electron beam irradiation for an extended time; the quenching was stronger for the free and shallow-donor-bound exciton peaks than for the defect-related peaks. The quenching appeared to saturate at high irradiation dose (with final intensity ≈30% of initial intensity) and was reversible on thermal cycling to room temperature. The electron irradiation-induced quenching of the CL is ascribed to charge injection and trapping phenomena.

Cathodoluminescence

10.1063/1.2736266

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Citations (35)

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

John B. Schlager Norman A. Sanford Kristine A. Bertness J. M. Barker Alexana Roshko

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High Field Transport Studies of GaN

physica status solidi (a) (2002)

J. M. Barker R. Akis T. J. Thornton D. K. Ferry S.M. Goodnick

We report on experimental and theoretical studies of high field transport in bulk GaN. Theoretically, we have investigated the electron–phonon interaction in this material based on empirical pseudopotential method (EPM) calculations for the bandstructure, together with an empirical valence shell model for the lattice dynamics in cubic GaN. The rigid-ion model is used to calculate the electron–phonon scattering rate for all modes, and to extract a deformation potential for use in high field transport calculations. A full band Monte-Carlo (FBMC) method is used to simulate high field transport in GaN. In the experimental studies, we have fabricated etched constrictions for performing pulse I–V measurements in bulk GaN and GaN/AlGaN heterostructures. The experimentally extracted velocity–field characteristics are in good agreement with transport calculations up to fields as high as 1.5 × 105 V/cm, where velocities up to 2.5 × 107 cm/s are measured.

Pseudopotential

Lattice (music)

10.1002/1521-396x(200203)190:1<263::aid-pssa263>3.0.co;2-u

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Citations (31)

Effects of surface treatment on the velocity–field characteristics of AlGaN/GaN heterostructures

Semiconductor Science and Technology (2004)

J. M. Barker D. K. Ferry Stephen M. Goodnick D. D. Koleske Andrew A. Allerman

AlGaN/GaN test structures were fabricated with an etched constriction. A nitrogen plasma treatment was used to remove the disordered layer, including natural oxides on the AlGaN surface, before the growth of the silicon nitride passivation film on several of the test structures. A pulsed voltage input, with a 200 ns pulse width, and a four-point measurement were used in a 50 Ω environment to determine the room temperature velocity–field characteristic of the structures. The samples performed similarly over low fields, giving a low-field mobility of 545 cm2 V−1 s−1. The surface treated sample performed slightly better at higher fields than the untreated sample. The highest velocity measured was 1.25 × 107 cm s−1 at a field of 26 kV cm−1.

Passivation

10.1088/0268-1242/19/4/157

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Citations (7)

Measurements of the velocity-field characteristic in AlGaN/GaN heterostructures

Microelectronic Engineering (2002)

J. M. Barker D. K. Ferry Stephen M. Goodnick D. D. Koleske A. E. Wickenden

Saturation velocity

10.1016/s0167-9317(02)00627-5

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Citations (14)

High field effects of GaN HEMTs.

J. M. Barker R. J. Shul

This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8x2, 10x3, 12x3, 12x4, 15x5, and 16x4 {micro}m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 {Omega} environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5x10{sup 7} cm/s at 180 kV/cm and 3.1x10{sup 7} cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively. These experimental drift velocities mark the highest velocities measured in these materials to date and confirm the predictions of previous theoretical models using ensemble Monte Carlo simulations.

Passivation

Ohmic contact

Contact resistance

10.2172/919143

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

Journal of Applied Physics (2007)

Lawrence H. Robins Kristine A. Bertness J. M. Barker Norman A. Sanford J B. Schlagear

NIST

Cathodoluminescence

Wide-bandgap semiconductor

Electron beam processing

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