scholarly journals Photoluminescence Studies of GaN and AlGaN Layers Under Hydrostatic Pressure

1995 ◽  
Vol 378 ◽  
Author(s):  
C. Wetzel ◽  
W. Walukiewicz ◽  
E. E. Haller ◽  
H. Amano ◽  
I. Akasaki
Keyword(s):  
Hydrostatic Pressure ◽  
Energy Levels ◽  
Wide Bandgap ◽  
High Electron ◽  
Valence Band Edge ◽  
Native Defects ◽  
Free Carriers ◽  
High Electron Concentration ◽  
Localized Defects ◽  
Photoluminescence Studies

AbstractWide bandgap GaN very often shows a high electron concentration. Although several impurities such as O and Si have been identified, the concentration is not high enough to account for the number of free carriers. As a consequence native defects namely the nitrogen vacancies are widely considered to be present at high densities. Several calculations predict different energy levels of this strongly localized defect. We present photoluminescence experiments of wurtzite GaN and AlGaN layers under large hydrostatic pressure to search for localized defects within the questionable energy range of 3 .0 to 3 .8 eV above the valence band edge.

Defect Studies of GaN under Large Hydrostatic Pressure

1995 ◽  
Vol 395 ◽  
Author(s):  
C. Wetzel ◽  
S. Fischer ◽  
W. Walukiewicz ◽  
J. Ager III ◽  
E.E. Haller ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Electron Concentration ◽  
Luminescence Band ◽  
Ambient Pressure ◽  
Conduction Band Edge ◽  
High Electron ◽  
High Electron Concentration ◽  
Strong Luminescence ◽  
Localized Defects ◽  
Strong Luminescence Band

ABSTRACTGaN plays a key role in the exploration of the properties of group-Ill nitrides. As grown GaN often shows a high electron concentration, e.g. 1019 cm−3, of as yet unidentified origin. Applying large hydrostatic pressure we studied the behavior of these donors and a frequently observed strong luminescence band at 3.42 eV. We find a drop of the electron concentration to 3×1017 cm−3 at 27 GPa and derive a binding energy of 126 meV for the neutral singlet donor level at this pressure. Such a pressure behavior of a donor is consistent with the model of strongly localized defects. Within the framework of a bandstructure calculation we predict the neutral level of this donor at 0.40 ± 0.10 eV above the conduction band edge at ambient pressure.

scholarly journals Properties of InGaN deposited on Glass at Low Temperature

1997 ◽  
Vol 2 ◽  
Author(s):  
Tilman Beierlein ◽  
S. Strite ◽  
A. Dommann ◽  
D. J. Smith
Keyword(s):  
Low Temperature ◽  
Indium Tin Oxide ◽  
High Electron ◽  
Transparent Conductor ◽  
High Background ◽  
X Ray ◽  
Substrate Heating ◽  
Glass Substrates ◽  
High Electron Concentration ◽  
Background Absorption

We have investigated the properties of InGaN grown at low temperature on glass substrates by a plasma enhanced MBE process. The goal of this study was to evaluate the potential of InGaN as an oxide-free, transparent conductor material which could be deposited at or slightly above room temperature with minimal interaction or damage to the underlying material. InxGa1−xN films deposited on glass, even without substrate heating, are highly crystalline, but the crystallinity as measured by x-ray degrades at x < 0.5. The microstructure observed by TEM of InGaN films deposited on unheated substrates is highly columnar, with typical column widths of ~10 nm. The optical absorption spectra of InGaN/glass have a distinct absorption edge at the bandgap, but also high background absorption in the bandgap. InxGa1−xN grown on glass (x > 0.5) is conductive due to its high electron concentration. InN electron Hall mobilities > 20 cm2/Vs when grown at 400°C, and ~ 7 cm2/Vs on unheated substrates were obtained. The addition of GaN degraded the electrical properties of the films to a greater extent than it improved the transparency. As a result, the best transparent conductor films were pure InN which, when deposited at 400°C, were half as transparent in the green as an indium tin oxide film having the same sheet resistance.

Polarization effects in AlxGa1−xN / GaN superlattices

2000 ◽  
Vol 639 ◽  
Author(s):  
Erik L. Waldron ◽  
E. Fred Schubert ◽  
John W. Graff ◽  
Andrei Osinsky ◽  
Michael J. Murphy ◽  
...  
Keyword(s):  
Room Temperature ◽  
Stark Effect ◽  
Blue Shift ◽  
Transition Band ◽  
Polarization Effects ◽  
Quantum Confined Stark Effect ◽  
Free Carriers ◽  
Bulk Gan ◽  
Band Transition ◽  
Photoluminescence Studies

ABSTRACTRoom temperature and low temperature photoluminescence studies of AlxGa1−xN/GaN superlattices reveal a red shift of the dominant transition band relative to the bulk GaN bandgap. The shift is attributed to the quantum-confined Stark effect resulting from polarization fields in the superlattices. A theoretical model for the band-to-band transition energies based on perturbation theory and a variational approach is developed. Comparison of the experimental data with this model yields a polarization field of 4.6 × 105 V/cm for room temperature Al0.1Ga0.9N/GaN and 4.5 × 105 V/cm for room temperature Al0.2Ga0.8N/GaN. At low temperatures the model yields 5.3 × 105 V/cm for Al0.1Ga0.9N/GaN and 6.3 × 105 V/cm for Al0.2Ga0.8N/GaN. The emission bands exhibit a blue shift at high excitation densities indicating screening of internal polarization fields by photo-generated free carriers.

Effect of Different Catalysts and Growth Temperature on the Photoluminescence Properties of Zinc Silicate Nanostructures Grown via VLS Method

2021 ◽  
Author(s):  
Ghfoor Muhammad ◽  
Imran Murtaza ◽  
Rehan Abid ◽  
Naeem Ahmad
Keyword(s):  
Energy Levels ◽  
Visible Region ◽  
Wide Bandgap ◽  
Visible Spectral Range ◽  
Zinc Silicate ◽  
Band Spectrum ◽  
Photoluminescence Properties ◽  
Display Devices ◽  
Crystal Growth Kinetics ◽  
Potential Applications

Abstract Herein, we explore the photoluminescence properties of zinc silicate (Zn2SiO4) nanostructures synthesized by vapor-liquid-solid (VLS) mode of growth using three different catalysts (Sn, Ag and Mn). Different catalysts significantly influence the growth rate which in turn has an impact on the structure and hence the photoluminescence of the prepared zinc silicate nanostructures. Zn2SiO4 has a wide bandgap of about 5.5 eV and in its pure form, it does not emit in visible region due to its inner shell electronic transitions between the 3d5 energy levels. However, the incorporation of different catalysts (Sn, Ag and Mn) at different growth temperatures into the Zn2SiO4 crystal growth kinetics provides wide visible spectral range of photoluminescence (PL) emissions. PL analysis shows broad multi-band spectrum in the visible region and distinct colours (red, yellow, green, blue, cyan and violet) are obtained depending on the crystalline structure of the prepared nanostructures. The allowed transitions due to the effect of different catalysts on zinc silicate lattice offer a huge cross-section of absorption that generates strong photoluminescence. The correlation between the structural and optical properties of the synthesized nanostructures is discussed in detail. The synthesized photoluminescent nanostructures have potential applications in solid-state lighting and display devices.

Terahertz conductivity of ultra high electron concentration 2DEGs in NTO/STO heterostructures

2016 ◽  
Author(s):  
Sara Arezoomandan ◽  
Hugo O. Condori Quispe ◽  
Ashish Chanana ◽  
Peng Xu ◽  
Ajay Nahata ◽  
...  
Keyword(s):  
Electron Concentration ◽  
High Electron ◽  
High Electron Concentration ◽  
Terahertz Conductivity

scholarly journals Systematic opacity calculations for kilonovae

2020 ◽  
Vol 496 (2) ◽  
pp. 1369-1392 ◽  
Author(s):  
Masaomi Tanaka ◽  
Daiji Kato ◽  
Gediminas Gaigalas ◽  
Kyohei Kawaguchi
Keyword(s):  
Near Infrared ◽  
Thermal Emission ◽  
Energy Levels ◽  
Blue Emission ◽  
Electron Shell ◽  
Infrared Emission ◽  
Atomic Data ◽  
High Electron ◽  
R Process ◽  
Process Elements

ABSTRACT Coalescence of neutron stars (NSs) gives rise to kilonova, thermal emission powered by radioactive decays of freshly synthesized r-process nuclei. Although observational properties are largely affected by bound–bound opacities of r-process elements, available atomic data have been limited. In this paper, we study element-to-element variation of the opacities in the ejecta of NS mergers by performing systematic atomic structure calculations of r-process elements for the first time. We show that the distributions of energy levels tend to be higher as electron occupation increases for each electron shell due to the larger energy spacing caused by larger effects of spin–orbit and electron–electron interactions. As a result, elements with a fewer number of electrons in the outermost shells tend to give larger contributions to the bound–bound opacities. This implies that Fe is not representative for the opacities of light r-process elements. The average opacities for the mixture of r-process elements are found to be κ ∼ 20–30 cm2 g−1 for the electron fraction of Ye ≤ 0.20, κ ∼ 3–5 cm2 g−1 for Ye = 0.25–0.35, and κ ∼ 1 cm2 g−1 for Ye = 0.40 at $T = 5000\!-\!10\, 000$ K, and they steeply decrease at lower temperature. We show that, even with the same abundance or Ye, the opacity in the ejecta changes with time by one order of magnitude from 1 to 10 d after the merger. Our radiative transfer simulations with the new opacity data confirm that ejecta with a high electron fraction (Ye ≳ 0.25, with no lanthanide) are needed to explain the early, blue emission in GW170817/AT2017gfo while lanthanide-rich ejecta (with a mass fraction of lanthanides ∼5 × 10−3) reproduce the long-lasting near-infrared emission.

Photoluminescence studies on self-organized 1.55-μm InAs/InGaAsP/InP quantum dots under hydrostatic pressure

2014 ◽  
Vol 116 (2) ◽  
pp. 023510 ◽  
Author(s):  
P. Y. Zhou ◽  
X. M. Dou ◽  
X. F. Wu ◽  
K. Ding ◽  
S. Luo ◽  
...  
Keyword(s):  
Quantum Dots ◽  
Hydrostatic Pressure ◽  
Self Organized ◽  
Photoluminescence Studies ◽  
Inp Quantum Dots

scholarly journals Photoluminescence studies of a GaAs-Ga1−xAlxAs superlattice at 8–300 K under hydrostatic pressure (0–70 kbar)

1985 ◽  
Vol 31 (6) ◽  
pp. 4106-4109 ◽  
Author(s):  
Umadevi Venkateswaran ◽  
Meera Chandrasekhar ◽  
H. R. Chandrasekhar ◽  
T. Wolfram ◽  
R. Fischer ◽  
...  
Keyword(s):  
Hydrostatic Pressure ◽  
Photoluminescence Studies
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