Table Of ContentWide Bandgap Semiconductor Power Devices
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Woodhead Publishing Series in Electronic
and Optical Materials
Wide Bandgap
Semiconductor Power
Devices
Materials, Physics, Design,
and Applications
Edited by
B. Jayant Baliga
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List of Contributors
Cornelius Armbruster Fraunhofer Institute for Solar Energy Systems ISE,
Freiburg,Germany
B.JayantBaliga NorthCarolinaStateUniversity,Raleigh,NC,UnitedStates
Ishwara Bhat Electrical Computer and Systems Engineering Department,
RensselaerPolytechnicInstitute,Troy,NY,UnitedStates
Subhashish Bhattacharya North Carolina State University, Raleigh, NC,
UnitedStates
T.PaulChow RensselaerPolytechnicInstitute,Troy,NY,UnitedStates
Srabanti Chowdhury Electrical and Computer Engineering, UC Davis, Davis,
California,UnitedStates
Chao Fei Center for Power Electronics Systems, Virginia Tech, Blacksburg, VA,
UnitedStates
ZhiboGuo RensselaerPolytechnicInstitute,Troy,NY,UnitedStates
Andreas Hensel Fraunhofer Institute for Solar Energy Systems ISE, Freiburg,
Germany
Patrick Hercegfi Fraunhofer Institute for Solar Energy Systems ISE, Freiburg,
Germany
Noriyuki Iwamuro University of Tsukuba, Faculty of Pure and Applied Sciences,
Tsukuba,Ibaraki,Japan
TsunenobuKimoto KyotoUniversity,Kyoto,Japan
Dirk Kranzer Fraunhofer Institute for Solar Energy Systems ISE, Freiburg,
Germany
Fred C. Lee Center for Power Electronics Systems, Virginia Tech, Blacksburg,
VA,UnitedStates
xii ListofContributors
Qiang Li Center for Power Electronics Systems, Virginia Tech, Blacksburg, VA,
UnitedStates
Stefan Scho¨nberger Fraunhofer Institute for Solar Energy Systems ISE, Freiburg,
Germany
Ju¨rgen Thoma Fraunhofer Institute for Solar Energy Systems ISE, Freiburg,
Germany
Yuchen Yang Center for Power Electronics Systems, Virginia Tech, Blacksburg,
VA,UnitedStates
Preface
In 1979, I derived a theoretical relationship between the specific on-resistance of
unipolar semiconductor power devices and the basic properties of the semiconduc-
tormaterialwhileemployedbytheGeneralElectricCompany.Mytheoryproduced
the Baliga’s figure-of-merit (BFOM) for power devices that can be used to predict
the performance enhancement produced by replacing silicon with wide bandgap
semiconductors. The most technologically mature semiconductor after silicon was
gallium arsenide (GaAs) at that time due to its applications for infrared lasers and
light emitting diodes. The BFOM predicted a13.6-foldreduction inthe specificon-
resistanceofunipolar power devices byreplacing siliconwithGaAs extendingtheir
applications to higher voltages and power levels. The existing manufacturing infra-
structure at GE for GaAs devices prompted its management to assign a team of 10
scientistsandtechnicianstoworkundermyguidancetocreateaGaAs-basedpower
device technology in the early 1980s. I organized a focused effort to create GaAs
epitaxiallayerswithlowerdopinglevelstomakehighvoltagedevices,createapro-
cess platformto makehigh performanceohmic andSchottkycontacts, and innovate
novel device structures to exploit the material. This effort culminated in the first
wide bandgap semiconductor power devices—Schottky rectifiers and vertical
metal(cid:1)semiconductor field-effect transistors—in the 1980s that validated the theo-
reticalpredictions.
My equation predicted a reduction in resistance by a factor of 200-times when
replacing silicon with silicon carbide using the know properties in the 1980s. By
the early 1990s, silicon carbide wafers became commercially available allowing the
demonstration ofthe first high voltage Schottkydiodesat the PowerSemiconductor
Research Center under my leadership in 1992. We were able to demonstrate a high
performance SiC power metal-oxide-field-effect transistor (MOSFET) using avail-
able 6H-SiC material in 1997. Measurements of the impact ionization coefficients
for silicon carbide under my direction provided data that increased the BFOM to
1000 for silicon carbide. These break-throughs encouraged major investments in
development of better material anddevices in the United States, Europe, and Japan.
The first commercial SiC product, a high voltage Junction Barrier Schottky (JBS)
diode, became available in the early 2000s. The market for these devices has now
grown to over $200 million due to their applications as antiparallel diodes for sili-
coninsulatedgatebipolartransistors(IGBTs)innumerousapplications.
After many years of effort to improve the interface properties between 4H-SiC
and thermally grown oxide, it became feasible to introduce the first SiC power
MOSFETs into the market in 2011. The initial concerns of application engineers
regardingthereliabilityofthese devices have beenovercomebyrigorous testingby
xiv Preface
the industry. The devices are now finding acceptance in applications such as PV
inverters and power supplies. The devices must compete against mature silicon
power devices—the IGBT and the superjunction FETs. The main impediment to
market growth has been the much higher cost of SiC power devices. Considerable
effort is underway around the world to drive down the cost of SiC power devices
whichportendsahealthymarketprojectionintothefuture.
The evolution of GaN power devices took an unusual path with the growth of
GaN layers on silicon substrates by using a transition layer toaccommodate the lat-
tice mismatch. This breakthrough has made the GaN high electron mobility transis-
tor (HEMT) structure possible with a highly conductive two-dimensional electron
gas layer. These lateral devices offer much superior drift region resistance.
However, it has been a challenge to create normally-off devices and even the
normally-on structures still suffer from dynamic on-resistance issues. Some compa-
nies have taken the approach of building normally-on GaN HEMT products using
the Baliga-Pair or Cascode configuration. Others have employed structural modifi-
cations to obtain a positive threshold voltage. These devices have been shown to
enable power circuits to operate at multi-MHz switching frequencies to make very
compact electronics possible. The ability to integrate multiple devices on a single
chipcreatesopportunitiestomakepowerICproductsaswell.
This book on wide bandgap semiconductor power devices was motivated by the
success of my book “The IGBT Device” published by Elsevier in 2015, which won
the prestigious PROSE award for the best book published that year in engineering
and technology. The IGBT book provided an extensive description of the applica-
tions of the IGBT in all sectors of our society and its social impact during the last
25years.
For this book on wide bandgap semiconductor power devices, I wanted to cover
the entire spectrum from material properties to device structures to their applica-
tions. I was pleased that all the people I approached to make contributions to the
book enthusiastically accepted my proposal. Unfortunately, some of the authors
failed to fulfill their promises due to commitments to their employers. Despite this,
the contents of this book provide a comprehensive discussion of the state of the art
for wide bandgap semiconductor power devices that is beneficial to the power elec-
tronicscommunity.
The book begins with an introductory chapter where I have provided an over-
view of the benefits of wide bandgap semiconductor materials for power devices.
Various types of power device structures are described in the chapter to familiarize
thereaderwiththetechnologydiscussedinmoredepthintherestofthebook.
Chapter 2, SiC material properties, prepared by Professor Kimoto from Kyoto
University, provides information on the basic properties of silicon carbide material
thatisrelevanttopowerdevicedesignandanalysis.Theemphasisisonthe4H-SiC
polytype because of its dominance for manufacturing SiC power devices. The dis-
cussion includes defects that influence the minority carrier lifetime due to its rele-
vanceforbipolarSiCpowerdevicessuchasveryhighvoltageIGBTs.
Chapter 3, Physical properties of gallium nitride and related III(cid:1)V nitrides, pre-
paredbyProfessorBhatfromRensselaerPolytechnicInstitute,providesinformation
Preface xv
on the basic properties of gallium nitride material. The electrical properties of the
two-dimensional electron gas in the AlGaN/GaN heterojunction structure are
included because of its importance to the lateral GaN HEMT devices that have
been commercialized. A discussion of defects produced during the growth of GaN
layers on silicon substrates is included here due to its relevance to the reliability of
thesedevices.
Chapter 4, SiC power device design and fabrication, prepared by Professor
Iwamuro from the University of Tsukuba, provides a comprehensive discussion of
silicon carbide power diodes and transistors. The physics of operation of SiC
P(cid:1)i(cid:1)N diodes and JBS rectifiers is described and their performance is quantified
for various blocking voltages. The design of a robust edge termination is critical to
maximizing their performance. An extensive discussion of the SiC power MOSFET
structure with either the planar or trench gate approach is provided. Good short-
circuit capability for these devices is essential to their acceptance in applications.
ThepotentialtodevelopveryhighvoltageSiCIGBTsisanalyzedhereaswell.
Chapter 5, GaN smart power devices and ICs, prepared by Professor Chow from
Rensselaer Polytechnic Institute, provides a thorough discussion of gallium nitride
power devices. Lateral power devices based up on GaN-on-Si technology with the
HEMT structure are covered in detail here. Prospects for making GaN-based power
ICsareincludedinthechapter.
Chapter 6, GaN-on-GaN power device design and fabrication, prepared by
Professor Chowdhury from University of California Davis, describes recent prog-
ress with design and fabrication of vertical GaN devices using bulk GaN substrates.
The challenges of making the CAVET structure with enhancement-mode operation
aredescribedhere.
Chapter 7, Gate drivers for wide bandgap power devices, prepared by Professor
Bhattacharya from North Carolina State University, highlights the importance of
providing adequate gate drive capability for wide bandgap semiconductor power
devices. The challenges and solutions for driving these devices to achieve higher
operating frequencies are described here. The operation of SiC and GaN devices at
higher frequencies offsets the higher cost of the devices due to reduction of size,
weight, and cost of passive elements. The chapter also provides insight into design-
ing drivers for very high blocking voltage IGBTs with extremely high dV/dt transi-
entsinpowercircuits.
Chapter 8, Applications of GaN power devices, prepared by a group of profes-
sors from Virginia Polytechnic Institute, describes potential applications for GaN
power devices. A number of converter designs implemented by the authors for
power supply applications are described here. The improvement in efficiency by
replacingsiliconwithGaNdevicesisquantifiedhere.
Chapter9, Applications of SiC devices, prepared by authors from the Franhaufer
Institute, provides a focused perspective of the benefits of silicon carbide power
devices on solar (PV) inverters. The benefits of replacing silicon devices with SiC
devicesforinverterefficiencyarequantifiedhere.
In the final chapter, I have provided a perspective on the history of wide band-
gap semiconductor power device development since 1980. Some technology trends
