Growth of undoped and doped IIInitride nanowires and their characterization [Elektronische Ressource] / vorgelegt von Ratan Kumar Debnath

Informations

• Publié par: rheinisch-westfalischen_technischen_hochschule_-rwth-_aachen
• Publié le: 01 janvier 2009
• Nombre de lectures: 47
• Langue: English
• Poids de l'ouvrage: 22 Mo

Extrait

Growth of Undoped and Doped III–Nitride
Nanowires and Their Characterization
Von der Fakultat¨ fur¨ Elektrotechnik und Informationstechnik
der Rheinisch-Westfa¨lischen Technischen Hochschule Aachen
zur Erlangung des akademischen Grades
eines Doktors der Ingenieurwissenschaften genehmigte Dissertation
vorgelegt von
Bachelor of Engineering
Ratan K. Debnath
aus Mymensingh, Bangladesch
Berichter: Universita¨tsprofessor Dr. Dr. h.c. H. Lut¨ h
Universit¨ atsprofessor Dr.-Ing. Rainer Waser
Tag der mundl¨ ichen Pru¨fung: 06. Februar 2009
Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfugbar.¨This thesis is dedicated to
my newly born daughter, Ahana Debnath;
my wife, Debjani Sarma;
and my parents, Prof. J. C. Debnath and Mrs. P. Debi.;Table of Contents
Table of Contents v
1 Introduction 1
2 Group III–Nitride Semiconductors 5
2.1 Introduction..................................... 5
2.2 CrystalStructure.................. 5
2.3 Substrates for III–Nitride Growth . . . . ..................... 7
2.4 EpitaxialGrowthofGaNandInN............ 8
3 Nanowires: An Overview 11
3.1 Introduction.....................................1
3.2 SynthesisofNanowires...............12
3.2.1 Vapor-Liquid-SolidGrowth........................12
3.2.2 Vapor-Solid-SolidGrowth.............13
3.2.3 Vapor-SolidGrowth............................13
3.2.4 ChemicalSolution-basedGrowth.........13
3.2.5 Template-asistedSynthesis........................14
3.3 II–NitrideNanowires...................14
3.4 Applications.................................15
3.5 Conclusion .........................16
4 Experimental Methods 17
4.1 MolecularBeamEpitaxy..............................17
4.2 ScanningElectronMicroscopy...............19
4.2.1 Cathodoluminescence ...........................20
4.3 TransmisionElectronMicroscopy ............20
4.4 PhotoluminescenceSpectroscopy.........................21
4.5 RamanSpectroscopy....................2vi TABLE OF CONTENTS
4.6 AtomicForceMicroscopy.............................2
4.7 X-rayPhotoelectronSpectroscopy ............23
5 Growth Mechanism of Nanowires 25
5.1 Introduction.....................................25
5.2 GrowthModeling..................25
5.3 NucleationStudies.................................27
5.4 Diffusion-inducedGrowth.................31
5.5 GrowthMechanism:FurtherInsights.......................3
6 GaN Nanowires: Growth and Characterization 37
6.1 GrowthMorphology................................37
6.1.1 Influence of Ga Flux and Substrate Temperature . . . . ....38
6.1.2 Template-asistedGrowth.........................40
6.1.3 Template-assistedGrowth:EffectsofGaFlux......45
6.1.4 Nanowires Grown on Si(100) . . .....................47
6.1.5 NanowiresGrownonOxidesandPaterning.......49
6.2 CathodoluminescenceSpectroscopy........................50
6.2.1 Nanowires Grown on Si(111) . ..........50
6.2.2 NanowiresonDotTemplates.......................54
6.2.3 FluxDependenceStudies.............56
6.2.4 Nanowires Grown on Si(100) . . .....................58
6.3 PhotoluminescenceSpectroscopy.............60
6.3.1 Nanowires Grown on Si(111) . . .....................60
6.3.2 GrowthonDotTemplates.............62
6.3.3 FluxDependenceStudies.........................65
6.4 RamanSpectroscopy....................67
6.5 HRTEMInvestigation...........................73
6.5.1 Nanowires Grown on Si(111) . ..........73
6.5.2 Nanowires Grown on SiO .........................7
2
7 InN Nanowires: Growth and Characterization 81
7.1 Growth Morphology on Si(111) . . . . . .....................81
7.2 PhotoluminescenceSpectroscopy.............85
7.3 HRTEMInvestigation...............................87
7.4 Growth Morphology on Ge(111) . . . ..........90
8 Doping in Nanowires 95
8.1 DopinginGaNNanowires.............................95
8.1.1 GrowthMorphology................95TABLE OF CONTENTS vii
8.1.2 CathodoluminescenceandPhotoluminescenceResults.........9
8.1.3 RamanSpectroscopy........................101
8.2 DopinginInNNanowires.....................102
8.2.1 GrowthMorphology........................102
8.2.2 PhotoluminescenceResults................104
9 GaN Nanodots 107
9.1 GrowthMorphologyandMechanism.......................107
9.2 SurfaceSpectroscopy....................13
10 Conclusions and Outlook 117
10.1Outlook.......................................18
Bibliography 119
List of Figures 133
List of Tables 139
Acronyms 141
List of Publications 143
Acknowledgements 145
Curriculum Vitae 147I am among those who think that science has great beauty.
A scientist in his laboratory is not only a technician: he is
also a child placed before natural phenomena which impress
him like a fairy tale.
–Marie Curie 1
Introduction
very field of science, technology and engineering in these modern days is blessed
by the application of “nanotechnology”. It is a young and burgeoning field in thisE twenty first century, which has become the main focus of scientists and engineers
and attracted the attention of general public. This field is defined primarily by a unit of
−9length, the nanometer (1 nm = 10 m), at which lies the ultimate control over the form
and function of matter. Indeed, the types of atoms and their fundamental properties are
governed by the laws of quantum physics. So the smallest scale, at which we have the
freedom to exercise our creativity is in the combination of various types and numbers of
atoms used to fabricate new forms of materials and devices. Such capabilities result in
properties and performance far superior to conventional technologies and in some cases,
allow access to entirely new phenomena only available at such small dimensions.
The rapid growth of this field in the past two decades has been enabled by the sus-
tained advances in the fabrication and characterization of increasingly smaller structures.
Various classes of structures such as carbon nanotubes, fullerenes, quantum wires and dots,
nanocomposites etc. have been realized. The discovery of novel materials, processes and
phenomena at the nanoscale, as well as further development of new experimental and the-
oretical techniques have provided great opportunities for the development of innovative
nanostructured materials and systems. Materials engineered into unique nanostructures
showed various unique and intriguing properties and applications, which can represent the
building blocks of new structures and devices. The emergence of two paradigms, referred as
top-down and bottom-up has accelerated the fabrication process. Parallel development in the
imaging and characterization of nanometer scale structures is also taking place worldwide.
Scanning-probe technology has indeed provided the atomic scale resolution for a number
of different physical properties such as electronic structure, morphology etc. In addition,
these microscopy techniques have enabled to modify surfaces at nanometer scale, and thus
supported their own set of approaches for the fabrication of small objects. This field is
opening up new venues in science and technology day by day.
Among various nanostructures, nanowires (NWs) are especially attractive for future
nanotechnology applications. NWs, compared to other low dimensional systems, have two
quantum confined directions while still leaving one unconfined direction for electrical con-
duction. This allows them to be used in applications, which require electrical conduction
rather than tunneling transport. Because of their unique density of electronic states, NWs
in the limit of small diameters can exhibit significantly different optical, electrical and mag-
netic properties from their bulk 3D crystalline structure. Large surface area, high density
of electronic states, enhanced exciton binding energy, diameter-dependent bandgap and in-
12 Chapter 1. Introduction
creased surface scattering for electrons and phonons are just some of the ways in which NWs
differ from their corresponding bulk materials.
In the semiconductor technology, most integrated circuits are practically developed on
Si substrates. However, III–V semiconductor materials have also gained more and more
importance in the last two decades. But Si and conventional III–V materials are not suit-
able for fabricating optoelectronic devices in the violet and blue region. Also, GaAs based
materials can not be used at high temperature. III–Nitrides (e.g. GaN, InN etc.) are
particularly suitable for application in these areas. Due to their large direct bandgap and
strong bonding, they have been used for the fabrication of high brightness blue light emitting
diodes (LEDs), laser diodes and high temperature transistors. Apart from optoelectronic
applications, nitride heterostructures play an important role in AlGaN/GaN based high
frequency, high electron mobility transistor devices. As a counterpart to planar structures,
III–Nitride NWs are expected to further improve the performance and efficiency of opto-
electronic device structures on the nanometer scale.
During the last ten years, a good number of research community has been involved
into the growth and characterization of III–Nitride NWs [1–5]. For device application, it is
important to have dense wires with controlled positions. So it is important to understan