Correlation between optical and electrical properties of materials containing nanoparticles

140 Pages·2008·3.81 MB·English

by  Alfredo Morales Sánchez

Universitat Autònoma
de Barcelona
Physics Department

Correlation between optical and electrical
properties of materials containing nanoparticles

Alfredo Morales Sánchez
Ph.D. Thesis

Director: Dr. Carlos Domínguez Horna
Co – Director: Dr. Mariano Aceves Mijares
Tutor: Dr. Javier Rodríguez Viejo

Barcelona, Spain
September 2008
ii
La presente tesis doctoral titulada: “Correlation between optical and electrical properties
of materials containing nanoparticles” ha sido realizada por Alfredo Morales Sánchez
como Trabajo de Investigación dentro del programa de Tercer Ciclo de Física bajo la
dirección de Carlos Domínguez Horna, Profesor de Investigación del Instituto de
Microelectrónica de Barcelona (IMB–CNM, CSIC) y Mariano Aceves Mijares,
Investigador Titular del Departamento de Electrónica perteneciente al Instituto
Nacional de Astrofísica, Óptica y Electrónica (INAOE) de México y actuando de tutor
el Dr. Javier Rodríguez Viejo, Profesor Titular del Departamento de Física de la
Universidad Autónoma de Barcelona.

Bellaterra, Barcelona. Septiembre 2008

Carlos Domínguez Horna Mariano Aceves Mijares

Javier Rodríguez Viejo

Acknowledgments

At first place, I want to thank Consejo Nacional de Ciencia y Tecnología (CONACyT)
and Fundación Carolina for the grant received.

My deepest thanks to Dr. Carlos Domínguez Horna for giving me the opportunity of
working under his direction and for his support and help during my stage in Barcelona,
Spain.

I would like to thank to Dr. Mariano Aceves Mijares for co-direct this work and for his
support and help.

Thanks to:
Dr. Javier Rodríguez Viejo for being my tutor at the Universidad Autónoma de
Barcelona.
Dr. Blas Garrido’s research group from the Universidad de Barcelona, Physics
department.
All the staff of the Instituto de Microelectrónica de Barcelona (IMB-CNM), especially to
the chemical transducers group (GTQ).
Instituto Nacional de Astrofísica, Óptica y Electrónica.

To projects:
MILES: “Monolithic integration of light emitters and optochemical transducers with
silicon technology”. TEC2006-13907-C04-01/MIC.
Optimization of silicon radiation sensors with high efficiency in the UV range. CSIC,
P2005MX03. Bilateral cooperation program CSIC-CONACYT.
NANOMAGO: Fabrication and characterization of thin magneto-optical layers in
metal-dielectric nanostructures: Implementation as modulators in integrated optics
technology. D.G.I. S.E.P.C. y T., MAT2002-04484-C03-01.

Finally, thanks to my family and my wife, Edith.
i
Abstract

It is known that bulk silicon is the dominant semiconductor material in
microelectronics. However, its use in reliable and low cost integrated circuits (IC)
fabrication which carry out opto-electronic functions has not been appropriate due to
the fact that silicon is an indirect band gap material.

Observation of luminescence in porous silicon seemed to solve the physical inability of
the silicon (Si) to act as light emitter; however its poor chemical stability, weak
robustness and luminescence degradation made it unsuitable for such applications.
Other Si-based materials such as hydrogenated silicon rich oxynitride, Si/SiO
2
multilayers, and silicon rich oxide (SiO , x<2) films have been reported to solve the
x
physical incapacity of silicon to act as light emitter. The key for the excellent light
emission properties of these materials are the embedded silicon nanoparticles (Si-nps).
With this approximation the quantum confinement of carriers is maximized, the
probability of radiative recombination is improved, and the emission wavelength is
shifted to the visible range and controlled with the Si-np’s size. These nanometre-sized
silicon particles either embedded in a SiO or Si N matrix have shown a strong and
2 3 4
stable luminescence seeming as a better alternative for light emitting devices (LED’s)
fabrication.

In this thesis, silicon rich oxide [SRO, (SiO , x<2)] films with different silicon excesses
x
were deposited by low pressure chemical vapor deposition (LPVCD). Besides, Si
implanted SRO (SI-SRO) films were also fabricated. Si-nps in these films were created
after a thermal annealing at high temperature (1100 and 1250º C). The composition,
microstructure and optical properties of these SRO and SI-SRO films were analyzed as
a function of the different technological parameters, such as silicon excess, Si ion
implantation dose, and thermal annealing temperature.

Once the microstructure, composition as well as the optical properties of these materials
is known, SRO films which exhibited the best photoluminescent (strongest PL)
properties were chosen in order to analyze their electrical and electro–optical properties.

ii
Simple Metal–Oxide–Semiconductor (MOS) structures using the SRO films as the
dielectric layer were fabricated for these studies. SRO films with Si-excess of ~4.0 and
~2.2 at.% and thickness ranging from 24 to 80 nm were deposited. The conduction
mechanism in these films is analyzed by making use of trap assisted tunnelling (TAT) in
low electric field as well as Fowler–Nordheim (FN) tunnelling in high electric fields.

The electrical measurements exhibited important results, such as a reduction in
capacitance and current during the sweep or after applying a constant bias. These effects
are ascribed to the annihilation of conduction paths created by silicon clusters (Si-cls)
inside the SRO films.

A part from that, some devices exhibited current fluctuations in the form of spike-like
peaks and a clear staircase at room temperature. These effects were related to Coulomb
blockade (CB) effects in the silicon nanoparticles embedded in the SRO films. And
from the current plateaus, the size of the Si-nps (about 1 nm) was calculated.

Field effect luminescence of these SRO films was studied by alternating negative
(positive) to positive (negative) voltages (pulsed excitation). Moreover, it is
demonstrated that these SRO films show EL emission in continuous current voltage,
observed at naked eye. Multiple shining spots of several colours are seen on the MOS-
like structure surface when reversely biased.

These devices display a broad electroluminescent emission spectrum which goes from
400 nm up to 900 nm. Finally, a correlation between the structural, electrical and
luminescent (PL and EL) properties is discussed.
iii
Contents

List of Symbols vi
Abbreviations viii
List of Figures xi
List of Tables xvii

1. Introduction 1
1.1. Bulk Silicon 1
1.2. Nanoparticles 2
1.3. Quantum confinement 3
1.4. Contents of this thesis 5
References

2. Luminescence in Silicon nanostructures 9
2.1. Porous silicon 9
2.2. Silicon nanoparticles 10
2.3. Fabrication techniques 11
2.4. Characterization techniques 13
References

3. Deposition and characterization of SRO and SI-SRO films 25
3.1. Material fabrication 25
3.2. Characterization of the material 28
3.2.1. Ellipsometry 28
3.2.2. Fourier Transform Infra-red Spectroscopy (FTIR) 29
3.2.3. X-ray Photoelectron Spectroscopy (XPS) 33
Analysis of Si2p-XPS peak 35
3.2.4. Energy Filtered Transmission Electron Microscopy (EFTEM) 37
3.2.5. Photoluminescence (PL) 42
3.3. Summary 46
References

iv
4. Fabrication and characterization of MOS-like devices 49
4.1. Fabrication process 49
4.2. Electrical characterization set-up 53
4.2.1. Electrical set-up 53
4.2.2. Electro-optical set-up 54
4.3. Electrical characterization results 56
4.3.1. C–w and C–V characteristics 56
4.3.2. I–V characteristics 63
4.4. Electro-optical characterization results 69
4.4.1. Pulsed electroluminescence 69
4.4.2. Continuous electroluminescence 72
4.5. Summary 78
References

5. Correlation between optical and electrical properties 81
5.1. Composition, microstructure and optical properties 81
5.2. Electrical properties 86
5.3. Electro-optical properties: Model verification 98

6. Conclusions and further work 113

List of publications 117

v
List of Symbols

A Area
C Capacitance
C Si-cluster capacitance
cl
C Flat-band capacitance
FB
C Maximum capacitance
MAX
C Minimum capacitance
MIN
C Capacitance between nanoparticles
np-np
C Oxide capacitance
ox
C Silicon surface capacitance
S
C Si-np capacitance
np
C Silicon dioxide capacitance
SiO2
C SRO capacitance
SRO
C Total capacitance
T
d Si-np size
δ Stairwidth current
i
E Electric field
Ec Coulomb charging energy
E Conduction band energy
C
E Fermi energy
F
Eg Band gap energy
Ei Intrinsic energy
E Electric field in the silicon dioxide
ox
E Valence band energy
V
f Frequency
I Current drop
drop
J Current density
K Dielectric constant of SRO
SRO
m* Effective mass of electron
e
m* Effective mass of hole
h
Na Density of acceptors
Neff Silicon/silicon rich oxide interface charge density
vi