MBE growth and characterization of multilayer structures for vertically emitting laser devices [Elektronische Ressource] / by Fernando Rinaldi

Informations

• Publié par: universitat_ulm
• Publié le: 01 janvier 2009
• Nombre de lectures: 44
• Langue: English
• Poids de l'ouvrage: 3 Mo

Extrait

MBE Growth and Characterization of Multilayer
Structures for Vertically Emitting Laser Devices
DISSERTATION
to obtain the academic degree of
DOKTOR-INGENIEUR
(DR.-ING.)
from the Faculty of Engineering Science and Computer Sciences
Ulm University
by
Fernando Rinaldi
from Catanzaro, Italy
Referees: Prof. Dr. rer. nat. Peter Unger
Prof. Carl E. Krill III, Ph.D.
Dean of the faculty: Prof. Dr. rer. nat. Helmuth Partsch
Oral examination: Ulm, April 23rd, 2008To Antje, the woman I love.Abstract
This work concerns molecular beam epitaxy (MBE) growth and characterization of
multilayer structures for vertically emitting laser devices. In particular, this thesis is
focused on the fabrication of novel VCSEL (vertical-cavity surface-emitting laser) and
VECSEL (vertical-external-cavity surface-emitting laser) multilayer structures grown on
GaAs substrate.
Several VCSEL structures for emitting wavelengths of 760, 850, and 980nm were
realized and the corresponding devices show high performance and have direct techno-
logical applications. As example, single-mode 760nm VCSELs are successfully employed
in oxygen sensing, or integrated VCSELs-photodetector systems allow bidirectional data
transmission in full-duplex mode at 2.5Gbit/s over 50m graded-index multimode fiber.
AsfarasregardVECSELs, samples fordevices having emitting wavelengths of850nm
and 980nm were produced. High-performance 850nm quantum-well-pumped VECSELs
having a slope efficiency of 67% were demonstrated.
The calibration techniques of the MBE system are described and applied to the prac-
tical cases of the growth of complex laser structures, therefore, an important part of this
work is devoted to HRXRD (high-resolution x-ray diffraction) analysis of the grown sam-
ples. This is a powerful tool to characterize not only the strain configuration and the
compositional profile of the layers, but also to indirectly monitor the molecular fluxes
improving the reliability of the MBE system.Acknowledgment
It is a pleasure for me to salute all the people that made possible the realization of
this work. I start with Frank Demaria, Ihab Kardosh, and Steffen Lorch, they are the
special friends I found in the Institute of Optoelectronics. For us there was no separation
between work and freetime, between work and fun. I wish everybody to find friends like
them. Also my thanks go to Dr. Manfred Mundbrod, he used to motivate me and he
really understood me.
A special thank goes to Susanne Menzel, we work close together since many years. I
learned everything about MBE exclusively fromher, andthis was a luck, because nobody
else has so much experience and so much understanding of this technique. I am also very
thankful to Michael Riedl, we spent together so much time on the MBE, that still runs
because Michael worked so hard also for me. I cannot forget Dr. Wladimir Schoch, he is
always ready to help me, to give good advice, and share his experience.
This thesis is ready just because all my colleagues transformed the samples I grew
in high-performance devices, these are Frank Demaria, Ihab Kardosh, Andrea Kroner,
Martin Stach, Abdel Sattar, Hendrik Roscher, Wolfgang Schwarz and were (because they
are already ”Doktoren”) Dr. Eckart Gester, Dr. Manmohan Singh, Dr. Johannes Michael
Ostermann and of course again the master of coatings Dr. Steffen Lorch. I am also
thankful to Ivan Savonov, Dr. Uwe Brauch from the University of Stuttgart for sharing
with us his expertise, and to Benjamin Scherer from the Fraunhofer-Institut in Freiburg.
Other people helped me and supported me everyday, like Su¨kran Kilic, who used to
cheer me up very often, and Rudolf R¨osch, who is the kind of person one can trust
completely.
I am grateful to the Prof.Ferdinand Scholz and to all the other members of the GaN
group for the support they gave me all over the years, expecially Peter Bru¨ckner and
Joachim Hertkorn.
So many students worked close to me as tight team, they are so many that I cannot
list them all, I want to make an exception for Onur Atilla, I thank him for the work he
did programming the p-doping control of the MBE I and for being my friend.
I still want to remember Dr. James O’Callaghan and Dr. Vincent Voignier, we had a
great time together.
IwanttomentionShunyiLi,whohadthemisfortuneofbeingmyfirstandonlystudent
I ever had. He had to stand and tolerate my egocentrism, my disorganization, and my
mood.
In this page there is obviously a place for Dietmar Wahl, we really have so much fun
working together, even though I can be arrogant, I hope he will forgive me for that. I
learned from him the basics of quantum dots and many other things.
I am so thankful to Dr. Rainer Michalzik for all the aid he gives to me in the V.O.I.
group and the work and time he spent with me bringing always new ideas.
To conclude, I am happy to greet my Professor, Prof. Peter Unger, who trusted in me,
giving me all the assistance I need and also the freedom in my work.
My life it is not just work, I also had my life outside the Institute. Therefore, I
should mention the complete Hagen family, and between them Martin, Andrea, SabineandMarkus,thesearepeopleIcanrelyon,andtheyweremyfirstGermanfriendstogether
with Frank Fiedler, now on his on way in Sweden.
A special place is reserved for Stephanie Wagner for staying always close to me. We
are the best friends one can imagine, and I feel I am a part of her family. It is really not
possible to express her my gratitude in this few lines.
I think I should apologize for my bad English, but nobody was happy when I propose
to write this work in Italian!
Thelastlineisdedicatedtomyfamily,whotriedtoencouragemedespitethedistance.Contents
1 Introduction 1
1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Structure of the thesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.3 Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2 Basics of molecular beam epitaxy 4
2.1 Overview of the MBE apparatus . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Effusion cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3 Thermodynamic approach . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3 Elasticity and physical properties in crystals 12
3.1 The strain tensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.2 The stress tensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
3.3 Hooke’s law in crystals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.4 The c and s tensors in cubic crystals . . . . . . . . . . . . . . . . . . . . . 16
3.5 The Poisson’s ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.6 Pseudomorphic (001) growth . . . . . . . . . . . . . . . . . . . . . . . . . . 19
3.7 The wafer bowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.8 Critical thickness and strain compensation . . . . . . . . . . . . . . . . . . 25
3.9 Nonlinear optical crystals. . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
4 Basics of VCSELs and VECSELs 33
4.1 VCSELs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.2 VECSELs or semiconductor disk lasers . . . . . . . . . . . . . . . . . . . . 35
4.3 Fresnel’s formulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
4.4 Multilayers, the transfer-matrix method. . . . . . . . . . . . . . . . . . . . 38
5 Basic x-ray diffraction theory 41
5.1 X-ray reflectometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
5.2 Dynamical theory of x-ray diffraction . . . . . . . . . . . . . . . . . . . . . 46
5.3 Detection of thin layers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
6 The molecular beam epitaxy system 50
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6.2 The effusion cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
6.3 Calibration of the sources . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
IContents
6.4 Calibration of the growth rates . . . . . . . . . . . . . . . . . . . . . . . . 55
6.5 AlGaAs calibrations based on photoluminescence . . . . . . . . . . . . . . 59
6.6 Growth rate profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.7 Pyrometer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.8 Doping calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.9 The arsenic source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.10 Residual gas analyzer (RGA) . . . . . . . . . . . . . . . . . . . . . . . . . 67
7 Reflection high-energy electron diffraction 73
7.1 Electron wavelength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
7.2 Kinematical approach to RHEED . . . . . . . . . . . . . . . . . . . . . . . 74
7.3 RHEED patterns on GaAs (001). . . . . . . . . . . . . . . . . . . . . . . . 75
8 High Performance VCSELs emitting at 760nm 82
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82
8.2 Layer structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
8.3 Wafer-level characterization . . . . . . . . . . . . . . . . . . . . . . . . . . 83
8.4 Lasers fabrication . . . . . . . . .