Copyright
by
Vijay Kumar Reddy
1994
CHARACTERIZATION OF HIGH FREQUENCY OSCILLATOR AND VARACTOR DIODES GROWN BY MOLECULAR BEAM EPITAXY
by
VIJAY KUMAR REDDY, B.S.E.E., M.S.E.E.
DISSERTATION
Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of
DOCTOR OF PHILOSOPHY
THE UNIVERSITY OF TEXAS AT AUSTIN
May 1994
This work is dedicated to my family for their loving support and encouragement
This work addresses the output power optimization of semiconductor based submillimeter wavelength power sources. This wavelength region, from 1 mm to 100 um (300 GHz to 3 THz), is of great importance in such applications as space-borne radio astronomy, spectroscopy, plasma diagnostics, and atmospheric remote sensing. Two candidate devices were investigated for their potential as submillimeter wavelength power sources: the double barrier resonant tunneling diode (DBRTD) and the heterojunction barrier varactor (HBV) diode. A reproducible molecular beam epitaxial growth process for AlAs/GaAs and AlAs/In0.53Ga0.47As devices was developed. The effect of a growth interruption at the DBRTD hetero-interface was studied and shown not to have a significant effect on the electrical characteristics. Furthermore, interface roughness at the normal and inverted interfaces was not found to play a significant role in determining high current density DBRTD transport characteristics.
The DBRTD oscillator output power is proportional to the [Delta]V[Delta]J power density product where [Delta]V is the difference between the peak and valley voltage and [Delta]J is the difference between the peak and valley current density. To increase [Delta]V, the downstream spacer layer profile is modified to take advantage of space-charge effects arising from carriers traversing a space-charge region at a constant saturation velocity. Such a layer modification results in the Quantum Well Injection Transit (QWITT) diode. To increase [Delta]J, devices should be fabricated in the AlAs/In0.53Ga0.47As material system which offers the highest [Delta]J possible. Record DC-to-RF continuous wave conversion efficiencies of 52% and output powers of 20 mW, the highest reported for DBRTD oscillators, were achieved with AlAs/In0.53Ga0.47As QWITTs.
HBV diodes intended as submillimeter-wavelength frequency multipliers were also studied. HBV diodes in the AlAs/In0.53Ga0.47As and AlGaAs/GaAs material system were investigated. The current transport in these structures was analyzed and record breakdown voltages as high as 12 volts were achieved. This result represents a significant breakthrough for the application of HBV diodes.
Links are to PDF versions of the original dissertation. To obtain a "fair use" copy of the material via the WWW send e-mail to Professor Dean Neikirk (neikirk@mail.utexas.edu) requesting the user name and password required to download the files. This material is not to be re-published in any form, electronic or otherwise, without permission of the copyright holder.
Chapter 1 Introduction.........................................................................................1
Chapter 2 Molecular Beam Epitaxy....................................................................4
2.1 Introduction to the Varian GEN II MBE System.....................................5
2.2 MBE Growth Kinetics..............................................................................8
2.3 Reflection High Energy Electron Diffraction (RHEED).........................11
2.4 Optimization of Growth Conditions for DBRTDs...................................16
2.5 Influence of growth interruption on the I - V characteristics of AlAs/
GaAs DBRTDs........................................................................................24
2.6 MBE Growth of InAlGaAs on InP...........................................................36
2.6.1 Growth issues for lattice-matched InGaAs on InP..........................37
2.6.2 InGaAs Growth Rate Calibration....................................................39
2.6.3 Critical Layer Thickness and Strained Layer Growth.....................42
2.7 InAlGaAs Epilayer Characterization........................................................46
2.7.1 Nomarski Optical Microscopy........................................................46
2.7.2 X-Ray Crystal Diffraction...............................................................50
2.7.3 Hall Mobility and Photoluminescence............................................55
2.8 Summary..................................................................................................57
Chapter 3 AlAs/In0.53Ga0.47As Double Barrier Resonant Tunneling
Diodes (DBRTDs)................................................................................59
3.1 Introduction .............................................................................................59
3.2 Self-consistent Schrodinger/Poisson DBRTD simulation.......................63
3.3 DBRTDs as High Frequency Devices......................................................67
3.4 AlAs/In0.53Ga0.47As: Material System of choice.....................................69
3.5 AlAs/In0.53Ga0.47As DBRTDs: barrier thickness dependence.................74
3.6 Comparison of Material Systems.............................................................79
3.7 Summary..................................................................................................81
Chapter 4 AlAs/In0.53Ga0.47As Quantum Well Injection Transit (QWITT)
Diodes ..................................................................................................82
4.1 Introduction.............................................................................................82
4.2 QWITT Linear J - E model.....................................................................88
4.3 AlAs/In0.53Ga0.47As QWITTs:...............................................................93
4.4 AlAs/In0.53Ga0.47As QWITTs: effect of drift region doping.................98
4.5 AlAs/In0.53Ga0.47As QWITTs: low sigma devices................................101
4.6 AlAs/In0.53Ga0.47As Depletion Edge Modulated QWITT
(DEMQWITT).......................................................................................104
4.7 Very High Efficiency Microwave Oscillators........................................109
4.8 Application of QWITTs to very high frequency oscillators...................112
4.9 Summary................................................................................................117
Chapter 5 Heterojunction Barrier Varactor Diodes........................................119
5.1 Introduction to varactor frequency multiplication..................................119
5.2 Schottky Diode Varactors......................................................................123
5.3 HBV Frequency Multipliers...................................................................124
5.4 AlGaAs/GaAs HBV Diodes...................................................................128
5.5 AlAs/In0.53Ga0.47As HBV Diodes..........................................................132
5.6 Summary................................................................................................140
Chapter 6 Summary and Conclusion................................................................141
Appendix 1 Device Fabrication Process............................................................144
Appendix 2 Summary of MBE runs grown on (mostly) InP substrates.....................................................................................146
References (also included at the end of each chapter) ............................................................................................................153
VITA......................................................................................................................170
ACKNOWLEDGEMENTS
I would like to first express my gratitude and appreciation for my advisor, Professor Dean P. Neikirk, for his guidance, inspiration, patience, and support. His incisive comments and suggestions have greatly improved this dissertation. To Professors Ben G. Streetman and Joe. C. Campbell, I thank them for their interest in this work and the use of their experimental facilities. I would also like to thank the other members of my committee: Professors Francis X. Bostick and John G. Ekerdt for their time and interest.
I would like to express my deep gratitude to the "ENS 405" gang: Doug Miller, Alwin Tsao, and Kiran Gullapalli for their friendship and invaluable help over the years. I thank Doug for our numerous discussions (a few technical) and for his thoughtful advice. To Alwin, I would like to express my thanks and appreciation for the experimental help, sharing his processing expertise, the wide ranging discussions, and the late-night rides home. I would like to thank Kiran for the many illuminating discussions that have greatly improved my understanding of DBRTDs and QWITTs, his considerable help in data analysis, and his careful reading of this work. I thank Carl "Yahoo Chuck Yeager" Kyono for his friendship, late nights jaunts, and his considerable help in processing matters. I would like to also express my thanks to Shiva Javalagi for many useful discussions on microwave oscillators and measurements. To the rest of "Team Neikirk": Saiful Islam, Jason Lewis, Vikas Gupta, Youngmin Kim, and Emre Tuncer, I extend my thanks for their friendship and help over the years. Also, I would like to thank the MBE group: Kayvan Sadra, Albert Shih, Anand Srinivasan, Tommy Rogers, Tom Block, Ananth Dodabalapur, Alex Anselm, and Chad Hansing for the many interesting discussions and friendship. I thank Terry Mattord for sharing his knowledge of vacuum systems and for keeping things working. I also would like to thank Bernice Wootton and Terrace Demerjian for their help in dealing with the bureaucracy and keeping things going smoothly.
Finally, I would like to acknowledge the financial assistance of the Texas Advanced Technology Program and the Joint Services Electronics Program without whose support this work could not have been undertaken.
Vijay Kumar Reddy, Ph.D.
The University of Texas at Austin, 1994
Supervisor: Dean P. Neikirk