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Charles University in Prague Universite Louis Pasteur Strasbourg I Faculty of Mathematics and Physics IPCMS GONLO Strasbourg

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164 pages
Niveau: Supérieur, Doctorat, Bac+8
Charles University in Prague Universite Louis Pasteur - Strasbourg I Faculty of Mathematics and Physics IPCMS/GONLO Strasbourg Czech Republic France These presentee pour obtenir le grade de Docteur de l'Universite Louis Pasteur (Universite Strasbourg I) Discipline: Optique Quantique et Optoelectronique par RNDr. Katerˇina Dohnalova Study of optical amplification in silicon based nanostructures Soutenue publiquement le 18 Septembre 2007 a Prague Membres du jury: Directeur de these: Bernd Honerlage Prof. Physique Codirecteur de these: Ivan Pelant Prof. Physique Rapporteur Interne: Jean-Jacques Grob DR,CNRS,HDR Physique Rapporteur Externe: Jiˇrı Cˇtyroky Prof. Physique Rapporteur Externe: Jean Oberle Prof. Physique Examinateur: Sˇtefan Viˇsnˇovsky Prof. Physique Examinateur: Jiˇrı Oswald Ing.,CSc. Physique Examinateur: Pierre Gilliot CR,CNRS,HDR Physique

  • optique quantique

  • spot d'excitation deplace

  • dfl cavity

  • shifting excitation

  • gain optique

  • nano-cristaux de silicium

  • physique examinateur

  • gain coefficient


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Charles University in Prague Universite Louis Pasteur - Strasbourg I
Faculty of Mathematics and Physics IPCMS/GONLO Strasbourg
Czech Republic France
These
presentee pour obtenir le grade de
Docteur de l’Universite Louis Pasteur (Universite Strasbourg I)
Discipline: Optique Quantique et Optoelectronique
par
RNDr. Katerina Dohnalov a
Study of optical ampli cation in silicon based
nanostructures
Soutenue publiquement le 18 Septembre 2007 a Prague
Membres du jury:
Directeur de these: Bernd H onerlage Prof. Physique
Codirecteur de these: Ivan Pelant Prof. Physique
Rapporteur Interne: Jean-Jacques Grob DR,CNRS,HDR Physique
Rapporteur Externe: Jir Ctyroky Prof. Physique
Rapporteur Jean Oberle Prof. Physique
Examinateur: Stefan Visno vsky Prof. Physique Jir Oswald Ing.,CSc. Physique
Examinateur: Pierre Gilliot CR,CNRS,HDR PhysiqueCharles University in Prague Universite Louis Pasteur - Strasbourg I
Faculty of Mathematics and Physics IPCMS/GONLO Strasbourg
Czech Republic France
Doctoral Thesis
"these en cotutelle"
Study of optical ampli cation in silicon based
nanostructures
by
RNDr. Katerina Dohnalov a
Prague & Strasbourg, September 2007Study of optical ampli cation in silicon based nanostructures
Supervisors:
Prof. RNDr. Ivan Pelant, DrSc.
Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
Prof. Dr. Bernd H onerlage
Institute de Physique et Chimie des Materiaux de Strasbourg, Universite Louis Pasteur,
Strasbourg, France
Advisors:
Prof. RNDr. Petr Maly, DrSc.
Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
Doc. RNDr. Jan Valenta, Ph.D.
Faculty of Mathematics and Physics, Charles University, Prague, Czech Republic
RNDr. Katerina Herynkova, Ph.D.
Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic
Referees:
Prof. Dr. Jean Oberle
Departements de Physique, Universite Bordeaux 1, Talence, France
Prof. Ing. Jir Ctyroky DrSc.
Institute of Photonics and Electronics, Academy of Sciences of the Czech Republic, Prague,
Czech Republic
Dr. Jean-Jacques Grob
Institut d’Electronique du Solide et des Systemes, Strasbourg, FranceAbstract
The aim of this work was to prepare light-emitting structure on the basis of silicon nanocrys-
tals (Si-ncs) embedded in a silicon dioxide (SiO ) based matrix of a su cien tly good optical2
quality and stable emission properties, which exhibits positive optical gain and can be used
as an active material in a laser cavity. The technique of sample preparation is based on a
combination of the modi ed electrochemical etching of silicon wafers and the SiO based2
sol-gel processing. This method enables us to achieve relatively small oxidized Si-ncs (2-
3 nm), embedded at virtually arbitrary volume fraction in a SiO based matrix, which is2
believed to be advantageous for easier stimulated emission (StE) onset observation. The
optical gain coe cien t was measured using the standard "Variable Stripe Length" (VSL)
method, the application of which, however, is limited for low gain. Therefore we imple-
mented a supplemental "Shifting Excitation Spot" (SES) method, enabling us to determine
the optical gain coe cien t even of such a small magnitude that will not be recognized by the
VSL method itself. We observed a positive net gain coe cien t originating from the StE in
di eren t Si-ncs/SiO samples under di eren t excitation and detection conditions. To pre-2
pare a laser system, a positive net gain observation is essential as well as a positive optical
feedback. Using an external cavity as a resonator requires a high optical quality sample.
This is, however, hardly achievable under the high Si-ncs volume fraction requirements for
the StE onset. Because of that we decided to build an optically induced "Distributed Feed-
back Laser" (DFL) system, where the cavity is distributed over the whole sample volume
and the cavity grating constant (166 nm) is lower than expected mean homogeneity length
in our sample (0.5-1.0 m). Therefore, a positive but low e ect on the emission of Si-ncs
is expected. Moreover, such type of DFL cavity is easily tuneable. The functionality of the
DFL setup was tested using reference organic dye solutions in methanol, where a tuneable
lasing action was successfully achieved. Similar tuneable cavity modes were also observed
in di eren t Si-ncs/SiO samples, however, of broader widths and less intense, compared to2
the organic dyes, which is mainly given by their lower optical quality. To understand and
describe the mode selection in such a material, we developed a simple theoretical model,
enabling us to determine the selected mode shape with respect to the sample homogeneity
length and the character of the inhomogeneities. We proved the active feedback of the
DFL cavity on the emission of our Si-ncs/SiO samples and proposed some further steps2
for future sample improvement.Resume
Le but principal de ce travaille fut de preparer un materiau photo-luminescent a base de
nano-cristaux de Silicium dans une matrice de silice (SiO ) de qualite optique su san te2
pour permettre l’observation d’un gain optique. Des nano-cristaux de silicium peu oxydes
de tailles comprises entre 2 et 3 nm ont ete obtenus par abrasion electrochimique de wafer
de silicium. Les nano-cristaux avec une concentration variable permettant l’observation de
leur emission stimulee sont dilues dans une matrice de silice obtenue par procede sol-gel.
Un dispositif optique dit "de zone a longueur variable" ("Variable Stripe Length" VSL) a
ete utilise pour la mesure du gain optique des nano-cristaux. Cependant cette methode
seule reste peu able pour les materiaux a faible gain optiques tels que les nano-cristaux
de silicium. Pour cette raison nous avons combine la methode VSL avec celle du "spot
d’excitation deplace " ("Shifting Excitation Spot" SES). Ceci nous permet d’observer des
gains faibles qui n’auraient pas pu ^etre atteint avec la methode VSL seule. Nos resultats
montrent clairement l’apparition d’un gain sous di erentes conditions d’excitations. Pour
preparer un laser il est necessaire d’avoir un materiau, montrant du gain optique, mais il faut
aussi appliquer une contra reaction optique su san te. L’utilisation d’une cavite optique ex-
terne necessite des echantillons de grande qualite optique. Ceci n’est pas compatible avec un
gain eleve qui demande une concentration tres forte en nano-cristaux de silicium. Pour cela
nous avons construit un laser a "cavite a contra reaction distribuee" ("Distributed Feedback
Laser" DFL). Dans ce type de cavite, la contra reaction est distribuee sur l’ensemble de
l’echantillon. Le pas du reseau (166 nm) est inferieure aux variations moyennes de densite
(0.5-1.0 m) et peut ^etre facilement modi e. Nous esperons ainsi obtenir un gain faible
mais su san t pour ^etre observable. La cavite DFL est tout d’abord calibree a l’aide de
di erents colorants dilues dans une solution de methanol ou nous avons observes des modes
laser biens de nis. Des modes d’emissions laser similaires (des pics plus larges et moins
intenses que dans le cas des colorants) ont ete obtenus dans nos echantillons Si-ncs/SiO .2
Ceci est principalement du^ a la moindre qualit optique de nos echantillons. Pour compren-
dre les precedentes observations, nous avons developpe un modele theorique simple nous
permettant de retrouver et d’expliquer les modes experimentaux en jouant sur la variation
de densite et les caracteristiques des Si-ncs. L’e et de la contra reaction de la cavite DFL
sur nos echantillons est clairement identi e par ce modele. Ceci nous permet d’entrevoir de
nouvelles perspectives pour la caracterisation optique et l’amelioration de nos echantillons.Abstrakt
Tato disertacn pr ace je venov ana studiu vzorku na b azi krem k ovyc h nanokrystalu (Si-
ncs) v SiO matrici. C lem je vyuzit techto vzorku jako aktivn ho prostred v laserovem2
rezon atoru, a proto byly pripravov any s durazem na optickou kvalitu, stabiln opticke vlast-
nosti a kladny opticky zisk. Vzorky jsou pripravov any metodou kombinuj c elektrochemicke
lept an krystalickeho krem ku a pr pra vu SiO matrice metodou sol-gel. Tato metoda2
umoznuje pripravit vzorky obsahuj c libovolne mnozstv malyc h Si-ncs (2-3 nm), coz je
povazov ano za vyho dne pro snazs pozorov an stimulovane emise. Opticky zisk jsme stu-
dovali metodou "Variable Stripe Length" (VSL), jejz presnost je ovsem v pr pad e nizs c h
hodnot optickeho zisku znacne omezen a. Z tohoto duvodu jsme navrhli metodu VSL rozsrit
o tzv. "Shifting Excitation Spot" (SES) metodu, kter a n am umoznuje merit i nizs hod-
noty optickeho zisku. Kombinac techto dvou metod jsme pozorovali kladny opticky zisk v
ruznyc h typech nasich vzorku za ruznyc h experiment aln c h podm nek. Pro pr pra vu laseru
je ovsem vedle kladneho optickeho zisku nutn a take pr tomnost kladne zpetne vazby. Pouzit
extern ho rezon atoru vyzaduje velmi vysokou optickou kvalitu aktivn ho materi alu, tezko
dosazitelnou v pr pad e nasich vzorku, kde je poreba pro dosazen optickeho zisku splnit
soucasne take podm nku vysoke hustoty Si-ncs v SiO matrici. Proto jsme se rozhodli2
pouz t jiny typ rezon atoru - laserem indukovanou mrzku ("Distributed Feedback Laser"
(DFL)). Mrzkov a konstanta rozlozene zpetne vazby je krats (166 nm) nez je charakteri-
stick a vzd alenost na nz je aktivn prostred dostatecne opticky homogenn (0,5-1,0 m),
d ky cemuz muzeme ocek avat kladny, i kdyz mens vliv zpetne vazby. Tento typ zpetne
vazby je nav c snadno laditelny. Funkcnost DFL zpetne vazby jsme testovali na organic-
kyc h barvivech, u nichz jsme usp esne pozorovali laserove mody. Podobne laditelne mody,
ovsem znacne rozsrene s nizs intenzitou (v porovn an s mody v organickyc h barvivech),
jsme pozorovali take ve spektrech nasich vzorku. Pro popis modove selekce ve vzorc c h
s nizs optickou kvalitou jsme vytvorili jednoduchy teoreticky model, umoznuj c charak-
terizovat homogenitu vzorku. Prok azali jsme aktivn vliv rozlozene zpetne vazby DFL na
emisn spektra nasich vzorku a navrhli jsme dals kroky k vylepsen jejich opticke kvality.Acknowledgements
First of all I would like to thank both my supervisors, Prof. RNDr. Ivan Pelant DrSc. and
Prof. Dr. Bernd H onerlage for their guidance and support during the research and writing of this
thesis. The major part of this work was done at IPCMS GONLO in Strasbourg (France) and De-
partment of Thin Films at IoP ASCR in Prague (Czech Republic). This concerns the experimental
work as well as the preparation of samples and the theoretical simulations.
My greatest thanks would belong to all other who helped me the most with the theoretical and
experimental part of this thesis: Ing. Olivier Cregut, RNDr. Tom as Ostatnicky Ph.D., Dr. Pierre
Gilliot, Dr. Dominique Ohlmann, Dr. Jean-Luc Rehspringer, Ing. Petr Br azda, RNDr. Katerina
Herynkov a Ph.D., RNDr. Katerina Kusov a, Dr. Kokou Dodzi Dorkenoo, Dr. Lo c Mager, Doc.
RNDr. Jan Valenta Ph.D., Prof. RNDr. Petr Maly DrSc., RNDr. Anton n Fejfar Ph.D. and others.
I want to express my thanks to Ing. Jean-Pierre Vola, MSc. Christelle Brimont, Dr. Steeve Cronen-
berger, Mr. Gilles Versini, Miss. Virginie Stortz, Dr. Mathieu Gallart, Ing. Jean-Luc Loison, Mr.
Gauthier Dekynt, Dr. Alain Carvalho and Ing. Emil S p ek CSc. and others for various technical
and theoretical assistance. I am very grateful to all my colleagues from IPCMS Strasbourg, Charles
University in Prague and Academy of Sciences of the Czech Republic, who provided their results and
contributed to the completion of this work. My thanks belong especially to Dr. Snejana Bakardjieva
PhD. from from UACH in Rez, Czech Republic and Dr. Sebastien Joulie from IPCMS Strasbourg
for the HRTEM measurements, Mgr. Karel Z dek, Doc. RNDr. Frantisek Troj anek Ph.D. and Doc.
RNDr. Jan Valenta Ph.D. from the Charles University in Prague for the time resolved measure-
ments with the fs excitation and the measurements of the optical properties of the ltered Si-ncs
colloids. We would like to thank also to Prof. Dr. E. Borsella from C.R. ENEA Frascati Roma
for the preparation of reference "Borsella" type of the silicon nanocrystals using laser pyrolysis.
My special thanks belong to RNDr. Jan Kocka DrSc. (head of the Thin Films Department in IoP
ASCR, Prague), Dr. Jean-Yves Bigot (head of the GONLO group in IPCMS, Strasbourg), Mgr.
Dagmar Z adrapov a, Petra Snajdrov a, Jeannine Drivon, Janine Joseph, Virginie Tigoulet and all the
laboratory sta in both institutes for the various support and friendly atmosphere.
Last, but not least, I would like to express my personal grateful thanks to Prof. Dr. Bernd
H onerlage and his wife Marja H onerlage and also to all my French friends and MSc. Nicolas Stenger
for their support and friendly help during my long-term stay in France, being the most important
period of my professional life. The most of all I would like to thank to all members of my family
and my partner PhDr. Miroslav Kotrle Ph.D. for their neverending tolerance and support.
This work was supported by the French government scholarship "these en cotutelle" of Ministry
of Education of France, the institutional Research Plan AV0Z 10100521, Centrum MSMT LC510
and Grant No. GAAVCR IAA1010316.
Prague & Strasbourg, September 2007 RNDr. Katerina Dohnalov aList of abbreviations and symbols:
Technology
CMOS Complementary Metal Oxide Semiconductor
EtOH ethanol
H O hydrogen peroxide2 2
HF Hydro- uoric acid
ITRS International Technology Roadmap for semiconductors
LED Light Emitting Diode
MeOH methanol
PECVD Plasma Enhanced Chemical Vapor Deposition
por-Si porous silicon
Si-ncs silicon nanocrystals
SiO dioxide2
TMOS tetrametoxysilane
Properties
e-h electron hole pair
FCA Free Carrier Absorption
FWHM Full Width in the Half of the Maxima
LO, LA phonons Longitudinal Optical and Acoustic phonons
QD Quantum dot
StE Stimulated Emission
STE Self-Trapped Exciton
TO, TA phonons Transverse Optical and Acoustic phonons
Measurement
-PL micro Photoluminescence
DFL Distributed Feedback Laser
FTIR Fourier Transformation Infrared Spectroscopy
HRTEM High Resolution Transmission Electron Microscopy
NA Numerical Aperture
PL Photoluminescence
PMT Photomultiplier
P&P Pump and Probe method
RTO Rapid Thermal Oxidation
SES Shifting Excitation Spot method
VSL Variable Stripe Length method
Institutes
AVCR Akademie Ved Ceske Republiky
ASCR(=AVCR) Academy of Sciences of the Czech Republic
FZU Fyzik aln Ustav
IoP(=FZU) Institute of Physics
IPCMS de Physique et Chimie des Materiaux de Strasbourg
GONLO Group d’Optique Nonlineaire1
Contents
1 Introduction - Silicon photonics and silicon-based laser 4
1.1 Interconnection bottleneck . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Silicon microphotonics . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1 Si-based laser diode . . . . . . . . . . . . . . . . . . . . . . . . 7
1.3 Outline of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2 Optical properties of oxidized Si-ncs 11
2.1 Stimulated emission in bulk crystalline silicon . . . . . . . . . . . . . 11
2.2 Optical properties of Si-ncs . . . . . . . . . . . . . . . . . . . . . . . . 14
2.2.1 Quantum con nemen t e ects . . . . . . . . . . . . . . . . . . 15
2.2.1.1 Symmetry breaking . . . . . . . . . . . . . . . . . . . 15
2.2.1.2 Atomic-like energy states . . . . . . . . . . . . . . . 15
2.2.1.3 Fermi Golden rule, oscillator strength and quasi-direct
recombination . . . . . . . . . . . . . . . . . . . . . . 16
2.2.2 Light emission in oxidized Si-ncs, surface/interface states . . . 18
2.2.3 Nonradiative processes . . . . . . . . . . . . . . . . . . . . . . 21
2.2.4 Stimulated emission in oxidized Si-ncs . . . . . . . . . . . . . 22
2.2.5 Laser on Si-ncs/SiO . . . . . . . . . . . . . . . . . . . . . . . 242
3 Preparation of Si-ncs/SiO samples 252
3.1 Electrochemical etching . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2 Si-ncs/SiO samples preparation . . . . . . . . . . . . . . . . . . . . . 292
3.2.1 Si-ncs powder treatment . . . . . . . . . . . . . . . . . . . . . 29
3.2.2 Embedding of the Si-ncs powder into an SiO sol-gel . . . . . 302
3.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4 Structural characterization of the samples 34
4.1 Size distribution estimation from HRTEM and Raman spectra . . . . 34
4.1.1 HRTEM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4.1.2 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 35
4.2 Surface investigation - FTIR spectroscopy . . . . . . . . . . . . . . . 37
5 Light emission and optical losses in Si-ncs/SiO samples 392
5.1 Attenuation and emission spectra of and pure SiO2 2
matrix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
5.1.1 SiO matrix optical properties . . . . . . . . . . . . . . . . . . 422
5.1.2 Si-ncs/SiO samples optical properties . . . . . . . . . . . . . 432
5.1.3 E ect of an additional H O treatment on the PL emission2 2
spectra of por-Si . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1.4 Green PL emission band observed in colloidal suspensions of
Si-ncs in EtOH . . . . . . . . . . . . . . . . . . . . . . . . . . 482
5.2 Time resolved PL emission spectra of Si-ncs/SiO samples . . . . . . 492
5.2.1 "Slow" PL emission component in Si-ncs/SiO samples . . . . 512
5.2.2 "Fast" PL component in . . . . 532
5.2.3 Time resolved PL emission intensity as a function of the the
pump intensity in Si-ncs/SiO samples . . . . . . . . . . . . . 582
5.2.4 "Ultrafast" PL dynamics in Si-ncs/SiO samples . . . . . . . . 592
5.3 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
6 Optical gain in Si-nc/SiO samples 622
6.1 Variable Stripe Length (VSL) and Shifting Excitation Spot (SES) tech-
niques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.1.1 VSL technique . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.1.2 One-dimensional (1D) VSL model . . . . . . . . . . . . . . . . 64
6.1.3 Limits of the VSL method . . . . . . . . . . . . . . . . . . . . 65
6.1.4 SES technique . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
6.1.5 VSL & SES methods for low gain measurements . . . . . . . . 68
6.1.6 Gain-like artifacts . . . . . . . . . . . . . . . . . . . . . . . . . 69
6.1.6.1 Pump beam di raction e ects . . . . . . . . . . . . . 70
6.1.6.2 Confocal e ect . . . . . . . . . . . . . . . . . . . . . 71
6.1.7 VSL & SES experimental setup . . . . . . . . . . . . . . . . . 71
6.1.7.1 VSL stripe and SES spot size, excitation intensity . . 74
6.2 Experimental results in solutions of organic dyes in methanol . . . . . 76
6.3 Exptal in Si-nc/SiO samples . . . . . . . . . . . . . . . 792
6.3.1 "Standard" 2nd sediment Si-ncs/SiO . . . . . . . . . . . . . . 812
6.3.1.1 "Slow" emission component . . . . . . . . . . . . . . 81
6.3.1.2 "Fast" component . . . . . . . . . . . . . . 86
6.3.1.3 Time-integrated measurements . . . . . . . . . . . . 88
6.3.2 "Standard" 4th sediment Si-ncs/SiO . . . . . . . . . . . . . . 912
6.3.3 Pure SiO matrix . . . . . . . . . . . . . . . . . . . . . . . . . 922
6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
7 Distributed Feedback Laser 96
7.1 DFL principle - Bor’s con guration . . . . . . . . . . . . . . . . . . . 97
7.2 Theoretical model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
7.2.1 Quality of the DFL cavity . . . . . . . . . . . . . . . . . . . . 99
7.2.1.1 Interference pattern quality . . . . . . . . . . . . . . 99
7.2.1.2 Nonlinear complex refractive index . . . . . . . . . . 102
7.2.2 Mode selection - theoretical model . . . . . . . . . . . . . . . 104
7.3 Cavity modes simulations in a low homogeneity material . . . . . . . 109
7.3.1 DFL di erence spectra . . . . . . . . . . . . . . . . . . . . . . 111
7.4 DFL experimental setup realization . . . . . . . . . . . . . . . . . . . 113
7.5 DFL results in reference samples - organic dyes in methanol . . . . . 115
7.6 DFL in Si-ncs/SiO samples . . . . . . . . . . . . . . . . . . . 1182
7.6.1 "Yellow" . . . . . . . . . . . . . . . . . . . . . . . 1182
7.6.2 "Standard" 2nd sediment Si-ncs/SiO . . . . . . . . . . . . . . 1232
7.6.3 4tht . . . . . . . . . . . . . . 1252
7.6.4 3rd sediment Si-ncs/SiO . . . . . . . . . . . . . . 1272
7.7 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128

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