Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics...

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Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute University of Amsterdam

Transcript of Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics...

Page 1: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

Absorption and generation of light with silicon nanocrystals in SiO2

Amsterdam Master of Physics Symposium 2008

Dolf Timmerman

Van der Waals-Zeeman InstituteUniversity of Amsterdam

Page 2: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

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Silicon

Indirect Bandgap

Ene

rgy

Momentum

Valence Band

Conduction Band

Phonon assisted transition

Silicon is a poor light-emitter

Indirect bandgap

Transitions need to overcome Δk

Radiative transitions phonon assisted

Amsterdam Master of Physics Symposium 2008

Photonics

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Nanocrystals

• Bandgap modification induced by quantum confinement

• Bands quantized energy levels• Relaxation of k-vector conservation rule, in

relation to indirect bandgap (Heisenberg)• Tuning optical properties

Silicon

4.3 nmSi NC

Amsterdam Master of Physics Symposium 2008

Page 4: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

SampleV

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SiO2

3.1 nm

Optical active layer containing silicon nanocrystals (and erbium)

Sample preparation, Kobe University

2 μm

Si - NC

Amsterdam Master of Physics Symposium 2008

σ = 14%

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ND:YAG Laser OPO

Spectro-meter

Sample

λ = 420 – 660 nmλ = 354 nm

5 ns 10 HzRoom-temperature

Setup

Amsterdam Master of Physics Symposium 2008

Page 6: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

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PL measurements

Si-NC

PL

Amsterdam Master of Physics Symposium 2008

Page 7: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

PhotoluminescenceV

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Time integrated PL-spectrum

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Page 8: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

Erbium V

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SiO2:(Er3+ +Si NC)

NC absorbs photon

Energy transfer to erbium

Erbium emits at 1.5 μm

Si-NC

1.5 μm

Er3+

Amsterdam Master of Physics Symposium 2008

One photon in one photon out

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Energy transfer

Amsterdam Master of Physics Symposium 2008

Page 10: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

Photoluminescence Er3+

)]exp(1[*

**)(

*

*

tNN

NNN

dt

dN

NI

PLEr

ErPL

PL

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Time integrated erbium PL flux-dependence Rate equations:

In the linear regime:

tNN PLEr *

The nr. of emitted photons is proportional to σPL

σPLis determined from PL intensity flux-dependence

Amsterdam Master of Physics Symposium 2008

NEr

NEr

Page 11: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

Absorption

Linear absorption

Absorbed fraction:

Absorbed photons:

Emitted photons:

Define relative quantum efficiency:

AbsNh

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I0I1

0

10

I

IIAbs

PLN *

PLh

Abs

N

N

*

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Relative quantum efficiency (η)V

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an - η is constant up to a certain photon energy threshold

- For larger photon energies a second excitation mechanism takes place

Q.E. for different wavelengths in visible and near UV.

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Quantum Cutting detected with Er3+V

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Si-NC

Er3+

0.8 eV

Er3+

Amsterdam Master of Physics Symposium 2008

Page 14: Absorption and generation of light with silicon nanocrystals in SiO 2 Amsterdam Master of Physics Symposium 2008 Dolf Timmerman Van der Waals-Zeeman Institute.

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Si-NC

Er3+Er3+

1 in 2 out

Amsterdam Master of Physics Symposium 2008

Quantum Cutting detected with Er3+

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η for Er3+V

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The quantum cutting process is less efficient for sample with larger NC-Er3+ distance

Two samples

- Identical Er3+ concentration and NC size

- Different NC concentration

- lower NC concentration larger average NC-Er3+ distance

Amsterdam Master of Physics Symposium 2008

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Amsterdam Master of Physics Symposium 2008

Relative quantum efficiency (η)

- η is constant up to a photon energy threshold of ≈ 2Eg

- For larger photon energies quantum cutting takes place.

Q.E. for different wavelengths in visible and near UV.

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Eex > 2EG

Quantum cutting with Si NCsV

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Eex < 2EG

Space-separated quantum cutting (SSQC)

Nature Photonics 2, 105-109 (2008)

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Conclusions Si NCs can be used to split energy quanta Erbium ions and neighboring NCs are used to detect

this Space separation in NCs gives long lifetime of excitons,

which is desired for applications

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Amsterdam Master of Physics Symposium 2008

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Amsterdam Master of Physics Symposium 2008