scholarly journals Photoluminescence in quantum-confined SnO2 nanocrystals: Evidence of free exciton decay

2004 ◽  
Vol 84 (10) ◽  
pp. 1745-1747 ◽  
Author(s):  
E. J. H. Lee ◽  
C. Ribeiro ◽  
T. R. Giraldi ◽  
E. Longo ◽  
E. R. Leite ◽  
...  
Keyword(s):  
Free Exciton ◽  
Sno2 Nanocrystals ◽  
Exciton Decay ◽  
Quantum Confined

Spectroscopic Studies in InGaN Quantum Wells

1998 ◽  
Vol 537 ◽  
Author(s):  
S. E Chichibu ◽  
T. Sota ◽  
K. Wada ◽  
S. P DenBaars ◽  
S. Nakamura
Keyword(s):  
Absorption Spectrum ◽  
Quantum Wells ◽  
Stark Effect ◽  
Free Exciton ◽  
Stokes Shift ◽  
Molar Fraction ◽  
Potential Wells ◽  
Piezoelectric Polarization ◽  
Quantum Disk ◽  
Quantum Confined

AbstractFundamental electronic modulations in strained wurtzite If-nitride, in particular InxGa1-xN, quantum wells (QWs) were treated to explore the reason why practical InGaN devices emit bright luminescences in spite of the large threading dislocation (TD) density. The emission mechanisms were shown to vary depending on the well thickness L and InN molar fraction x. The electric field across the QW plane, F, which is a sum of the fields due to spontaneous and piezoelectric polarization and the pn junction field, causes the redshift of the ground state resonance energy through the quantum confined Stark effect (QCSE). The absorption spectrum is modulated by QCSE, quantum-confined Franz-Keldysh effect (QCFK), and Franz-Keldysh (FK) effect from the barrires when, for the first approximation, potential drop across the well (F/L) exceeds the valence band discontinuity, δEv. Under large F/L, holes are confined in the triangular potential well formed at one side of the well. This produces apparent Stokes-like shift in addition to the in-plane net Stokes shift on the absorption spectrum. The QCFK and FK further modulate the electronic structure of the wells with L greater than the three dimensional (3D) free exciton (FE) Bohr radius, aB. When F/L exceeds ΔEc, both electron (e) and hole (h) confined levels drop into the triangular potential wells at opposite sides of the wells, which reduces the wavefunction overlap. Doping of Si in the barriers partially screens the F resulting in a smaller Stokes-like shift, shorter recombination decay time, and higher emission efficiency. Finally, the use of InGaN was found to overcome the field-induced oscillator strength lowering due to the spontaneous and piezoelectric polarization. Effective in-plane localization of the QW excitons (confined excitons, or quantized excitons) in quantum disk (Q-disk) size potential minima, which are produced by nonrandom alloy potential fluctuation enhanced by the large bowing parameter and F, produces confined e-h pairs whose wavefunctions are still overlapped when L<aB. Their Coulomb interaction is more pronounced for F L<ΔEv.

Dynamics of the Nitrogen Bound Excitons in 6H and 3C SiC

1994 ◽  
Vol 339 ◽  
Author(s):  
J. P. Bergman ◽  
C. I. Harris ◽  
O. Kordina ◽  
A. Henry ◽  
E. Janzén
Keyword(s):  
Decay Time ◽  
Low Temperatures ◽  
Strong Dependence ◽  
Free Exciton ◽  
Auger Process ◽  
Photoluminescence Decay ◽  
Donor Binding Energy ◽  
Decay Times ◽  
Exciton Decay ◽  
Exciton Decay Time

AbstractWe have measured the photoluminescence decay time of the bound excitons at the neutral nitrogen donors in the 6H and 3C polytypes of SiC. At 2K the decay times are 8.0 ns, 1.8 ns and 1.5 ns, for the P, R and S bound excitons in 6H SiC. For the nitrogen exciton in 3C, we find a decay time of 160 ns. These values are faster than previously reported for shallow donors in other indirect bandgap materials such as Si or GaP. Each of the observed decay times is found to be independent of the doping level in the sample, is temperature independent at low temperatures but decrease when the bound excitons are thermally ionised. The decay time related to different donor levels in 6H exhibits a strong dependence on the donor binding energy. We suggest that the dominant mechanism responsible for the observed decay time is a phonon-less Auger process. In high-purity 6H samples we have also measured the free exciton decay time at low temperatures to be 12 ns.

Ultraviolet free-exciton light emission in Er-passivated SnO2 nanocrystals in silica

2006 ◽  
Vol 89 (15) ◽  
pp. 153126 ◽  
Author(s):  
S. Brovelli ◽  
N. Chiodini ◽  
F. Meinardi ◽  
A. Lauria ◽  
A. Paleari
Keyword(s):  
Light Emission ◽  
Free Exciton ◽  
Sno2 Nanocrystals

scholarly journals Spectroscopic Studies in InGaN Quantum Wells

1999 ◽  
Vol 4 (S1) ◽  
pp. 93-105 ◽  
Author(s):  
S. F. Chichibu ◽  
T. Sota ◽  
K. Wada ◽  
S. P. DenBaars ◽  
S. Nakamura
Keyword(s):  
Absorption Spectrum ◽  
Quantum Wells ◽  
Stark Effect ◽  
Free Exciton ◽  
Stokes Shift ◽  
Molar Fraction ◽  
Potential Wells ◽  
Piezoelectric Polarization ◽  
Quantum Disk ◽  
Quantum Confined

Fundamental electronic modulations in strained wurtzite III-nitride, in particular InxGa1−xN, quantum wells (QWs) were treated to explore the reason why practical InGaN devices emit bright luminescences in spite of the large threading dislocation (TD) density. The emission mechanisms were shown to vary depending on the well thickness L and InN molar fraction x. The electric field across the QW plane, F, which is a sum of the fields due to spontaneous and piezoelectric polarization and the pn junction field, causes the redshift of the ground state resonance energy through the quantum confined Stark effect (QCSE). The absorption spectrum is modulated by QCSE, quantum-confined Franz-Keldysh effect (QCFK), and Franz-Keldysh (FK) effect from the barrires when, for the first approximation, potential drop across the well (FL) exceeds the valence band discontinuity, EV. Under large FL, holes are confined in the triangular potential well formed at one side of the well. This produces apparent Stokes-like shift in addition to the in-plane net Stokes shift on the absorption spectrum. The QCFK and FK further modulate the electronic structure of the wells with L greater than the three dimensional (3D) free exciton (FE) Bohr radius, aB. When FL exceeds EC, both electron (e) and hole (h) confined levels drop into the triangular potential wells at opposite sides of the wells, which reduces the wavefunction overlap. Doping of Si in the barriers partially screens the F resulting in a smaller Stokes-like shift, shorter recombination decay time, and higher emission efficiency. Finally, the use of InGaN was found to overcome the field-induced oscillator strength lowering due to the spontaneous and piezoelectric polarization. Effective in-plane localization of the QW excitons (confined excitons, or quantized excitons) in quantum disk (Q-disk) size potential minima, which are produced by nonrandom alloy potential fluctuation enhanced by the large bowing parameter and F, produces confined e-h pairs whose wavefunctions are still overlapped when L<aB. Their Coulomb interaction is more pronounced for FL<EV.

AN ANALYSIS OF ELECTRON–HOLE RECOMBINATION IN SOLID KRYPTON USING TIME-RESOLVED VUV-LUMINESCENCE SECTROSCOPY

2002 ◽  
Vol 09 (02) ◽  
pp. 783-788 ◽  
Author(s):  
V. KISAND ◽  
M. KIRM ◽  
S. VIELHAUER ◽  
G. ZIMMERER
Keyword(s):  
Free Exciton ◽  
Band Gap Energy ◽  
Electron Hole ◽  
Time Resolved ◽  
Detailed Model ◽  
Model Calculations ◽  
Exciton Decay ◽  
Solid Krypton ◽  
First Time ◽  
Hole Recombination

For the first time, the free exciton (FE) VUV-luminescence decay curves were systematically investigated in solid Kr using photoexcitation in the energy region above band gap energy. Delayed electron–hole recombination and "prompt" (in terms of the time resolution of the experimental setup) creation of secondary excitons were separated using the time-resolved experimental technique. A detailed model for the dynamics of electron–hole recombination into the FE state was developed. The delayed component of the free exciton decay curve was reproduced with model calculations, including thermalization of the carriers via scattering on acoustic phonons, and the recombination cross-section, which depends on the actual carrier temperatures. A satisfactory agreement between experiment and theory was found.

The quantum confined Pockels effect in GaAs-based multi-quantum wells

1999 ◽  
Vol 09 (PR2) ◽  
pp. Pr2-37 ◽  
Author(s):  
O. Krebs ◽  
P. Voisin ◽  
D. Rondi ◽  
J. L. Gentner ◽  
L. Goldstein ◽  
...  
Keyword(s):  
Quantum Wells ◽  
Pockels Effect ◽  
Quantum Confined

Light-Induced Drift of Quantum-Confined Electrons in Semiconductor Heterostructures

1990 ◽  
Author(s):  
Mark I. Stockman ◽  
Lakshmi N. Pandey ◽  
Thomas F. George
Keyword(s):  
Semiconductor Heterostructures ◽  
Quantum Confined
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