_ Group meeting, Feb. 2003 ___ Manuel Forcales

___________________________________________Group meeting, Feb. 2003_____________________________________________

Manuel ForcalesManuel Forcales

OPTICAL MEMORY EFFECT OPTICAL MEMORY EFFECT IN Si:ErIN Si:Er


_____________________Van der Waals-Zeeman Institute, University of Amsterdam________________

Free Electron Laser facility for Infrared eXperiments (FELIX)

&

AcknowledgementsGroup members from the Van der Waals–Zeeman Institute (WZI):Group members from the Van der Waals–Zeeman Institute (WZI):

M. A. J. Klik , N.Q. Vinh, Dr. M. Wojdak andM. A. J. Klik , N.Q. Vinh, Dr. M. Wojdak and

Dr. T. GregorkiewiczDr. T. Gregorkiewicz

FOM Institute “Rijnhuizen” (FEL Facility) staff members:FOM Institute “Rijnhuizen” (FEL Facility) staff members:

Dr. I. Bradley, Dr. J-P.R. WellsDr. I. Bradley, Dr. J-P.R. Wells

Samples kindly provided by:Samples kindly provided by:

Dr. A. Polman, AMOLF, The NetherlandsDr. A. Polman, AMOLF, The Netherlands

Dr. Widdershoven, PRL, The NetherlandsDr. Widdershoven, PRL, The Netherlands

Dr. F. Priolo, IMETEM, ItalyDr. F. Priolo, IMETEM, Italy

Dr. W. Jantsch, University of Linz, AustriaDr. W. Jantsch, University of Linz, Austria

Dr. J. Michel, MIT, USADr. J. Michel, MIT, USA

Financial support (thank$):Financial support (thank$):

ARL-ERO, NWO, FOMARL-ERO, NWO, FOM



Outline

Motivations

Photoluminescence (PL) experiments

Results

Conclusions



Introduction: data storage/Er3+ excitation

Intro I: Optical data storage



Need for all-optical data storage writing, reading and erasing by photons

...

write

read

electronics

CDProcess of writing Thermal in nature (melt, cool down)

All optical process All optical process FAST FAST

Approaches:

- Holographic optical storage (IBM, Lucent)

- Hole burning

Optical memory effect observed in III-V semicond., but never in SiOptical memory effect observed in III-V semicond., but never in Si

Motivation for using Si



Why Si?Why Si?

King of electronicsKing of electronics

Environmentally friendlyEnvironmentally friendly

Total control of dopantsTotal control of dopants

potential for photonics?potential for photonics?(Integration of electronics and photonics, on-chip)(Integration of electronics and photonics, on-chip)

Motivation for using erbium (Er)



Why Er?Why Er?

Are there other rare earth (RE) elements available?Are there other rare earth (RE) elements available?

Inner 4f-electron shell transitionsInner 4f-electron shell transitions

Emission at 1.54 Emission at 1.54 m (telecommunications)m (telecommunications)

Sharp transitions in wavelengthSharp transitions in wavelength

Almost independent of host materialAlmost independent of host material

Silicon doped with rare earths

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Ce3+ Pr3+ Nd3

+ Pm3+ Sm3+ Eu3+ Gd3+ Tb3+ Dy3+ Ho3+ Er3+ Tm3+ Yb3+

RE ground state

Si bandgap



Er3+ excitation in an insulator (SiO2)



Er3+ ion

Direct Er3+ excitation 10-21 cm-2

All erbium can be excited

OPTICALLY

Er PL @ 1.54 m

We need laser to pump Er.

We need resonant energies.

ELECTRICALLY

Electron impact excitation10-14 cm-2

LED with quantum efficiencies 10 % (similar to III-V semicond.)

STMicroelectronics“New York Times, Oct. 2002 ”

Patent by STM

Er 12 ms

Solution ? Use sensitizers like nc-Sinc-Si

BAD !

EDFA

Optical Er3+ excitation sensitized with nc-Si



Ernc-Sinc-Si

Current investigations are based on:

-Excitation spectroscopy (power and wavelength dependence) CW or pulsed

-Kinetics (rise time, decay time), temperature dependence…

Dr. Wojdak ;-)

How many optically active Er? , Excitation cross section?,

Excitation/ Energy transfer mechanism?, Possibility to obtain GAIN?

Er

Optical Er3+ excitation in crystalline Si

Indirect excitation 10-15 cm-2 increased 6 orders of magnitude !

Generation of carriers optically band-to-band excitation E > Egap (1170 meV) (also possible electrically)

Er3+ ion

Nd

:YA

G

VB

CBCB

Er-related allows recombination level (electron and hole) Er3+ excitation

Role of shallow traps excitation / de-excitation? Mid infrared radiation

Source FREE ELECTRON LASER

Er-related



Er 1 ms

Er3+ de-excitation in crystalline Si

Back-transfer Provided by E (thermally or by FEL )

Ionization of traps may induce excitation or Auger de-excitation

Er3+ ion

VB

CB

Er-related



+E

Thermal effects quench completely RT emission Thermal effects quench completely RT emission at 1.54 at 1.54 mm

Er3+ ion Er3+ ion

Energy migrationEnergy migrationEr3+ ion Er3+ ion

Up-conversionUp-conversion

> Egap

Free Electron Laser (FEL) facility

High brilliance and precise energy tuning: (70-170) meV

The magnetic field generates periodically curved electron trajectory



The induced oscillating dipole moment leads to emission of radiation

Photoluminescence experimental set-upT = 4.2 K

sample

Ge

/ PM

T

emission @ 1.54 emission @ 1.54 mm

SpectrometerSpectrometer

Follow changes in:- Spectrum- Amplitude- Kinetics

Tunable delay time (t) and variable power

Nd:YAG (532 nm)Nd:YAG (532 nm)

FEL (10 FEL (10 m )m ) t



Experimental set-up (real one)



1500 1550 1600 1650

Er ions implanted: energy: 300 keV dose: 3*1012 cm-2

Er-concentration: 5*1017cm-3

Oxygen ions co-implanted: energy: 40 keV dose: 3*1013 cm-2

annealing: 900 oC (N2 atmosphere) time: 30 minutes.

Inte

nsit

y

Wavelength (nm)

1.5 m

0 10 20 30

Time (ms)

Inte

nsit

y a

t 1.5

m

1 ms

Photoluminescence of Si:Er



0 5 10 15

Nd:YAG

Time (ms)

PL

at 1

.54 m

(ar

b. u

nits

)

FEL

Afterglow and Er PL enhancement

Er PLEr PL

Nd:YAG

FEL

afterglow 100-150 ms

4.2 K



No effect when FEL is fired before Nd:YAG

0 50 100 150 200

enhancement

~ 150 ms

FEL

FELFEL

E

r P

L at

1.5

4 m

(ar

b. u

nits

)

Time (ms)

Dynamics of the enhancement effect

afterglow enhancement

M. Forcales et al., Phys. Rev. B 65, 195208 (2002)



Model

VB

CB

Er3+

matrixN

d:Y

AG

, A

r+

FEL

Er-related level

Er PL



Temperature dependence



0 5 10 15 20

t

1 2

Time (ms)

PL

at 1

.54 m

(ar

b. u

nits

)

0 5 10 15 20

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Time (ms)

PL

at

1.5

4

m (

no

rma

lize

d) 20 K

30 K

Single carrier excitation

0.00 0.01 0.02 0.03 0.04 0.05

PL

at 1

.54 m

(no

rmal

ized

)

Power FEL (normalized)

0.0 0.2 0.4 0.6 0.8 1.0

Power FEL (normalized)

P

L a

t 1

.54

m

(n

orm

aliz

ed

)

Enhancement effect does not follow (IFEL)2, quadratic dependence

Er3+ ion

VB

CBCB

Er-related

IFEL

Incorrect Model

M. Forcales et al., Phys. Rev. B 67, 0853xx (2003)



0.0 0.2 0.4 0.6 0.8 1.0

0.0

0.5

1.0

1.5

2.0

2.5

MIR photon flux

En

han

cem

en

t am

plitu

de

FEL = 14 m

fits the trap-ionization dependence:

p = (-II+sqrt(I2I2+4I cINtr))/2c

Dependence on flux



Ionization of traps

Enhancement has a dependence related to one carrier excitation

Concept of a Si-based optical storage element

Storage array Storage element

Writing beam λ1

(band-to-band)

Recovered signal at 1.54 m

Reading beam λ2

(below band gap)

M. Forcales et al., Solid State Electronics, vol. 47, 165 (2003)



Futures perspectives

--Need to improve thermal stability!Need to improve thermal stability!How? Using deeper acceptor traps (Zn, Mg).How? Using deeper acceptor traps (Zn, Mg).

-No need to use free electron laser!-No need to use free electron laser!How? Table-top OPO, COHow? Table-top OPO, CO22 or cascade lasers… or cascade lasers…

-Creation of electrons and holes separated in Creation of electrons and holes separated in time!time!How? Prepare the system by proper injection How? Prepare the system by proper injection of carriers.of carriers.

VB

CBCB

Er-related

Atr

Si-based optical elements could find applications in:Si-based optical elements could find applications in:- Telecommunication networks at 1.54 - Telecommunication networks at 1.54 mm- Optical storage devices for use in all-photonic - Optical storage devices for use in all-photonic technologytechnology- Quantum computing ?…- Quantum computing ?…



Conclusions

Observation of afterglow and optical memory Observation of afterglow and optical memory effect in Si:Er system at temperatures T < 50 Keffect in Si:Er system at temperatures T < 50 K

The effect is a fundamental property of silicon The effect is a fundamental property of silicon (revealed by the optical dopant Er)(revealed by the optical dopant Er)

Proper engineering, will allow long time storage Proper engineering, will allow long time storage and thermal stabilityand thermal stability



Documents

___________________________________________ Group meeting, Feb. 2003 _____________________________________________ Manuel Forcales

_ Group meeting, Feb. 2003 ___ Manuel Forcales