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Title: Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride

Abstract

Time-dependent cathodoluminescence (CL) and specimen current (SC) are monitored to evaluate trapping behavior and evolution of charge storage. Examination of CL and SC suggests that the near band edge emission in GaN is reduced primarily by the activation of traps upon irradiation, and Gallium vacancies are prime candidates. At the steady state, measurement of the stored charge by empiric-analytical methods suggests that all available traps within the interaction volume have been filled, and that additional charge is being stored interstitially, necessarily beyond the interaction volume. Once established, the space charge region is responsible for the steady state CL emission and, prior to build up, it is responsible for the generation of diffusion currents. Since the non-recombination effects resulting from diffusion currents that develop early on are analogous to those leading to device failure upon aging, this study is fundamental toward a holistic insight into optical properties in GaN.

Authors:
;  [1];  [2];  [3]
  1. School of Electronic Engineering, Bangor University, Gwynedd LL57 1UT (United Kingdom)
  2. Department of Chemistry and Biochemistry, University of the Science, Philadelphia, Pennsylvania 19104 (United States)
  3. Department of Electrical and Computer Engineering, Missouri University of Science and Technology, Rolla, Missouri 65409 (United States)
Publication Date:
OSTI Identifier:
22596674
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 24; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AGING; CATHODOLUMINESCENCE; CURRENTS; DIFFUSION; FAILURES; GALLIUM; GALLIUM NITRIDES; IRRADIATION; OPTICAL PROPERTIES; RECOMBINATION; SPACE CHARGE; STEADY-STATE CONDITIONS; TIME DEPENDENCE; TRAPS; VACANCIES

Citation Formats

Campo, E. M., E-mail: e.campo@bangor.ac.uk, Hopkins, L., Pophristic, M., and Ferguson, I. T. Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride. United States: N. p., 2016. Web. doi:10.1063/1.4954685.
Campo, E. M., E-mail: e.campo@bangor.ac.uk, Hopkins, L., Pophristic, M., & Ferguson, I. T. Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride. United States. doi:10.1063/1.4954685.
Campo, E. M., E-mail: e.campo@bangor.ac.uk, Hopkins, L., Pophristic, M., and Ferguson, I. T. 2016. "Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride". United States. doi:10.1063/1.4954685.
@article{osti_22596674,
title = {Simultaneous specimen current and time-dependent cathodoluminescence measurements on gallium nitride},
author = {Campo, E. M., E-mail: e.campo@bangor.ac.uk and Hopkins, L. and Pophristic, M. and Ferguson, I. T.},
abstractNote = {Time-dependent cathodoluminescence (CL) and specimen current (SC) are monitored to evaluate trapping behavior and evolution of charge storage. Examination of CL and SC suggests that the near band edge emission in GaN is reduced primarily by the activation of traps upon irradiation, and Gallium vacancies are prime candidates. At the steady state, measurement of the stored charge by empiric-analytical methods suggests that all available traps within the interaction volume have been filled, and that additional charge is being stored interstitially, necessarily beyond the interaction volume. Once established, the space charge region is responsible for the steady state CL emission and, prior to build up, it is responsible for the generation of diffusion currents. Since the non-recombination effects resulting from diffusion currents that develop early on are analogous to those leading to device failure upon aging, this study is fundamental toward a holistic insight into optical properties in GaN.},
doi = {10.1063/1.4954685},
journal = {Journal of Applied Physics},
number = 24,
volume = 119,
place = {United States},
year = 2016,
month = 6
}
  • We have used cathodoluminescence spectroscopy with variable incident beam energies to study the energy levels and activation of Er impurities in GaN as a function of depth below the free surface. The GaN films were doped {ital in situ} during either metalorganic molecular-beam epitaxy (MOMBE) or molecular-beam epitaxy (MBE). Besides the well-known Er{sup 3+} luminescence at 0.80 eV, we observe emissions at 1.2, 1.8, 2.2, and 2.3 eV, corresponding to higher energy Er 4{ital f} shell transitions. For unannealed MOMBE-grown GaN:Er, these higher energy emissions appear only for excitation depths of hundreds of nanometers. The MOMBE-grown GaN;Er annealed to 500&hthinsp;{degree}Cmore » shows a dramatic increase in the 1.8, 2.2, and 2.3 eV peak intensities at shallow probe depths, with its yield increasing with increasing depth. These three features become pronounced at all depths after a 700&hthinsp;{degree}C anneal. MBE-grown GaN:Er grown with lower C and O impurity levels than the MOMBE-grown sample exhibits strong emission at all these energies without annealing. The decreased emission at shallow (tens of nanometer) probe depths suggests a depletion of activation Er in the near-surface region. Enhancement of near-surface Er{sup 3+} luminescence with annealing may be due to lattice reordering as well as impurity redistribution. {copyright} {ital 1999 American Vacuum Society.}« less
  • Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between themore » GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710? C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620? C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of ? three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620? C, but no such layer was observed for the substrate temperature of 710? C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface.« less
  • Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between themore » GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710 deg. C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620 deg. C. Ex situ atomic force microscopy and transmission electron microscopy analyses showed that the dot size distribution was bimodal. A thin GaN continuous layer of {approx} three monolayers thick was observed by transmission electron microscopy on the sample grown at a substrate temperature of 620 deg. C, but no such layer was observed for the substrate temperature of 710 deg. C. This suggests that there is little mobility of Ga atoms in contact with the sapphire substrate at the lower temperature so that they cannot easily diffuse to nearby droplets and instead form a thin layer covering the surface.« less
  • This Letter reports the thermal conductivity of aluminium nitride (AlN) thin-films deposited by reactive DC magnetron sputtering on single-crystal silicon substrates (100) with varying plasma and magnetic conditions achieving different crystalline qualities. The thermal conductivity of the films was measured at room temperature with the transient hot-strip technique for film thicknesses ranging from 100 nm to 4000 nm. The thermal conductivity was found to increase with the thickness depending on the synthesis conditions and film microstructure. The conductivity in the bulk region of the films, so-called intrinsic conductivity, and the boundary resistance were in the range [120-210] W m{sup -1}more » K{sup -1} and [2-30 Multiplication-Sign 10{sup -9}] K m{sup 2} W{sup -1}, respectively, in good agreement with microstructures analysed by x-ray diffraction, high-resolution-scanning-electron-microscopy, and transmission-electron-microscopy.« less