Transmission electron microscopy investigations of the CdSe based quantum structures [Elektronische Ressource] / submitted by Elena Roventa

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• Physik

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• Publié par: universitat_bremen
• Publié le: 01 janvier 2006
• Nombre de lectures: 19
• Langue: English
• Poids de l'ouvrage: 15 Mo

Extrait

Transmission electron microscopy investigations
of the CdSe based quantum structures
Elena Roventa
University of Bremen
2006Transmission electron microscopy investigations
of the CdSe based quantum structures
Ph.D. thesis
to obtain the academic degree
Doctor in Natural Sciences
— Dr. rer. nat. —
of the Fachbereich 1
at the University of Bremen
submitted by
Dipl. Phys. Elena Roventa
1. Examinator: Prof. Dr. rer. nat. Andreas Rosenauer
2. Prof. Dr. rer. nat. Detlef Hommel
Day of examination: 22.09.2006Contents
Introduction v
1 Theoretical background 1
1.1 II VI compounds based on ZnSe . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.1 Crystal structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1.2 Physical properties and material parameters . . . . . . . . . . . . . 3
1.2 Epitaxial growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.1 Growth modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.2.2 Molecular Beam Epitaxy . . . . . . . . . . . . . . . . . . . . . . . . . 10
1.2.3 Migration Enhanced Epitaxy . . . . . . . . . . . . . . . . . . . . . . 11
1.3 Defects in crystal structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1.3.1 Dislocations and stacking faults . . . . . . . . . . . . . . . . . . . . 14
1.3.2 and in zincblende structures . . . . . . 17
1.3.3 Defects in heterostructures . . . . . . . . . . . . . . . . . . . . . . . 19
2 Experimental techniques 23
2.1 Basic principle of an electron microscope . . . . . . . . . . . . . . . . . . . 23
2.2 Theory of electron diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . 26
2.2.1 Interaction between the electron beam and crystal . . . . . . . . . . 26
2.2.2 Kinematic approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
2.2.3 Dynamical theory of electron diffraction: Bloch wave approach . . 34
2.3 Image formation in an electron microscope . . . . . . . . . . . . . . . . . . 39
2.3.1 Theory of image formation . . . . . . . . . . . . . . . . . . . . . . . 39
2.4 Imaging modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
2.4.1 Bright field and Dark field mode . . . . . . . . . . . . . . . . . . . . 45
2.5 Sample preparation for TEM . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.5.1 Cross section geometry . . . . . . . . . . . . . . . . . . . . . . . . . 49
2.5.2 Plan view . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.6 Complementary experimental techniques . . . . . . . . . . . . . . . . . . . 52
2.6.1 Photoluminescence . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
2.6.2 Electroluminescence . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
2.6.3 High resolution X ray diffraction and grazing incidence small an
gle X ray scattering . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
3 Degradation of Cd rich quaternary quantum well laser diodes 59
3.1 Research status and motivation . . . . . . . . . . . . . . . . . . . . . . . . . 59
3.2 Growth of quaternary CdZnSSe quantum well . . . . . . . . . . . . . . . . 62
iContents
3.3 Analysis of as grown CdZnSSe quantum well . . . . . . . . . . . . . . . . . 63
3.4 Operational characteristics and degradation . . . . . . . . . . . . . . . . . . 67
3.4.1 Electroluminescence measurements . . . . . . . . . . . . . . . . . . 67
3.4.2 Lifetime measurements . . . . . . . . . . . . . . . . . . . . . . . . . 69
3.5 Analysis of CdZnSSe degraded quantum well . . . . . . . . . . . . . . . . 70
3.6 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
3.7 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
4 Chemical distribution in CdSe/ZnSSe superlattices 77
4.1 Research status and motivation . . . . . . . . . . . . . . . . . . . . . . . . . 77
4.2 Growth design of quantum dot stacks . . . . . . . . . . . . . 78
4.3 Transmission electron microscopy investigations . . . . . . . . . . . . . . . 79
4.4 Chemical composition of CdSe and ZnSSe layers . . . . . . . . . . . . . . . 79
4.4.1 Experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
4.4.2 Evaluation of the chemical composition . . . . . . . . . . . . . . . . 81
4.4.3 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
5 Spatial ordering of the CdSe dots in CdSe/ZnSSe stack structures 95
5.1 Research status and motivation . . . . . . . . . . . . . . . . . . . . . . . . . 95
5.2 Transmission electron microscopy investigations . . . . . . . . . . . . . . . 95
5.2.1 Influence of the spacer layer thickness . . . . . . . . . . . . . . . . . 96
5.2.2 Dependence on the number of the stacks . . . . . . . . . . . . . . . 102
5.2.3 Anisotropy of the quantum dot correlation . . . . . . . . . . . . . . 106
5.3 Grazing incidence small angle X ray measurements . . . . . . . . . . . . . 110
5.4 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
6 Summary and conclusion 115
Bibliography 125
iiAbbreviations
AFM Atomic Force Microscopy
bcc body centred cubic
BF Bright field
BFP Back focal plane
CCD Charge coupled device
CL Chatodoluminescence
COLC Centre of Laue Circle
CTF Coherent transfer function
DALI Digital Analysis of Lattice Images
DF Dark field
DFT Density functional theory
DLD Dark line defects
DP Diffraction pattern
DSD Dark spot defects
DVD Digital Video Disc
EDX Energy dispersive X ray Spectroscopy
EL Electroluminescence
EMS Electron Microscopy Image Simulation
fcc face centred cubic
FE finite element
FIB Focus Ion Beam
FWHM full width at half maximum
GISAXS Grazing incidence small angle X ray scattering
HAADF high angle annular dark field
HRTEM high resolution transmission electron microscopy
HRXRD High r X ray diffraction
LASER light amplification by stimulated emission of radiation
LD laser diode
LED light emitting diode
MBE molecular beam epitaxy
MOCVD metal organic chemical vapour deposition
MEE migration enhanced epitaxy
OTF Object transfer function
PL photoluminescence
PSD position sensitive detector
REDR Recombination enhanced defect reaction
REDC dislocation climb
REDG enhanced glide
QD quantum dot
QW well
relrod reciprocal lattice rod
RHEED reflection high energy electron diffraction
RT room temperature
SAD selected area diffraction
XPS X ray Photospectroscopy
iiiivIntroduction
Optical communication systems have progressed very rapidly from the research labs
into commercial applications. They have already been established within transport
networks as point to point links, broadcast distribution and interconnecting electrical
nodes. Currently the progress of this technology is significant in the diffusion of multi -
wavelength extended capacity links with wavelength routing at the nodes and add
drop operation of the high data flowing in the domain. Future optical communications
networks for terabyte transmission rates require the use of optical routing to cope with
ever increasing capacity demand due to growing Internet traffic. In addition, another
important role plays the data storage, where light also can provide a solution. Optical
data storage systems (ex. DVD) permit to store the information with a high density and
fast access.
The special requirement for both applications is the use of a proper light source as
monochromatic as possible and of a defined color. Moreover, light with a high inten
sity and easy to focus even over long distances is needed. Additionally, the source has
to be small, efficient, robust and cheap. Semiconductor lasers, in which the semicon
ductor serves as photon source, provide such a monochromatic coherent light of high
intensity as a result of light amplification by stimulated emission of radiation (LASER).
Furthermore, the rapid development of semiconductor technology allows the produc
tion of small devices with high reliability. This leads to the conclusion that, in our days,
the semiconductor laser diodes are one of the best light sources used in communication
technology.
However, the application range of semiconductor lasers goes beyond the commu
nication area. In fact, our everyday life is surrounded by laser applications which are
included in laser pointers, (used to make a bright spot to point with), navigation system
for aircraft navigation (semiconductor laser driven gyroscope about the size of a com
puter chip), laser sights for rifles and guns, health science (use in diagnosis, surgery and
imaging), biotechnology etc. One of the most interesting application of lasers is the dis
play technology. Using lasers, new, sharp and brilliant displays with a color spectrum
can be fabricated in a very small size.
Since the realization of the first electrically pumped laser diode in 1962, in the last
40 years these devices transformed from pure academic curiosities to commercial pro
ducts that can be found almost everywhere. Semiconductors lasers are most commonly
made from the III V semiconductors GaAs/AlGaAs (for light with a wavelength around
850 nm) or InP/InGaAsP (for 1.5 μm). The current injected into a forward biased p n
junction creat