Department of Physics, Chemistry and Biology (IFM), Linköping University
activity report
2015
STAFF
Professors
Erik Janzén (Head of Division)
Peder Bergman
Per Olof Holtz
Leif Johansson (Emeritus)
Bo Monemar (Emeritus)
Nguyen Tien Son
Einar Sveinbjörnsson
Rositsa Yakimova (Emerita)
Associate Professors (Docents)
Vanya Darakchieva
Urban Forsberg
Carl Hemmingsson
Ivan Ivanov
Chariya Jacobi
Anelia Kakanakova
Fredrik Karlsson
Olof Kordina
Plamen Paskov
Henrik Pedersen
Mikael Syväjärvi
Qamar ul Wahab
Assistant Professors, Research fellows & Lecturers
Örjan Danielsson
Jawad ul Hassan
Tino Hofmann (Guest Lecturer)
Jianwu Sun
Volodymyr Khranovskyy
Gholam Reza Yazdi
Chih-Wei Hsu
Post doctors
Philipp Kühne
Houssaine Machhadani
Daniel Nilsson (ended Dec.)
Ivan Shtepliuk (ended June)
Jr-Tai Chen (started June)
PhD students
Nerijus Armakavicius
Chamseddine Bouhafs
Ian Booker (PhD Oct.)
Jr-Tai Chen (PhD June)
Martin Eriksson
Andreas Gällström (PhD June)
Tomas Jemsson (Lic Jan.)
Valdas Jokubavicius
Robin Karhu
Xun Li (PhD June)
Louise Lilja
Björn Lundqvist
Björn Magnusson
Yuchen Shi (started Sept.)
Pontus Stenberg
Pitsiri Sukkaew
Xuan Thang Trinh (PhD June)
Thien Duc Tran (PhD Oct.)
Chao Xia (PhD Oct.)
Administrative / Technical Staff
Sven Andersson
Roger Carmesten
Ildiko Farkas
Tihomir Iakimov
Rickard Liljedahl
Xinyu Liu
Vallery Stanishev
Kerstin Vestin
Eva Wibom
Visiting Scientists (at least one month stay)
Michael Michailov, Bulgarian Academy of Sciences,
Sofia, Bulgaria
Kateryna Shavanova, Univ. of Life and
Environmental Sciences, Ukraine
Alla Tereshchenko, Odesa National Mechnikov
National Univ., Ukraine
Mengyao Xie, Technical Univ. of Madrid, Spain
Visiting Graduate Students (at least one month stay)
Noor Ul Ain, the Islamia Univ. of Bahawalpur,
Pakistan
Inna Burkova, Univ. of Life and Environmental
Sciences, Ukraine
Takahide Hirasaki, Tokyo Univ. of Agriculture and
Technology, Japan
Priya Darshni Kaustik,!Jamia Millia Islamia
University, Delhi, India
Sean King, Univ. of Nebraska-Linclon, USA
Yuliia Ruban, Univ. of Life and Environmental
Sciences, Ukraine
Yauhen Viazau, Inst. of Biophysics and Cell
Engineering, Belarus
INTRODUCTION
The Semiconductor Materials Division develops and
investigates materials for novel electronics with the
main focus on silicon carbide (SiC), III-nitrides
(GaN, InN, AlN and their alloys) and graphene. The
goal is to resolve fundamental and applicationmotivated issues of interest for Swedish and
European industries. The research activities within
the division cover a broad spectrum dominated by
basic research, mainly funded by Swedish and
European agencies, partly with industrial
collaboration. There is a strong international
cooperation within most research projects.
Current research activities
• Growth, simulation and characterization of
epitaxial films and bulk crystals.
• Investigations of crystal defects and doping.
• Development and studies of nano- and
heterostructures.
The growth is based on chemical vapor deposition
(CVD) or sublimation techniques while the
characterization includes surface and interface
properties as well as structural-, optical- and
transport properties probed by techniques such as
photoluminescence spectroscopy, magnetic
resonance, DLTS, ellipsometry, XRD, photoelectron
spectroscopy and microscopy.
III-nitride or SiC based single-photon emitters are
fabricated and investigated for their potential use in
quantum information applications. Other optically
efficient materials, e.g. zinc oxide (ZnO), are also
studied.
High frequency and high power
SiC is a semiconductor
material that sustains
higher frequencies,
powers and
temperatures than
conventional silicon.
This leads to smaller
electronics and reduced power loss, with
applications in electric power distribution and power
electronics in hybrid cars. Significant efforts within
the division are devoted to develop high quality SiC
for devices. One ambition is to control the involved
isotopes and thereby improve its thermal properties.
Vanya Darakchieva selected for SSF's research
infrastructure fellows
The goal of this project is to build upon current
developments of the only Terahertz (THz)
ellipsometer in Europe and establish a central openaccess facility at IFM, Linköping University: The
Terahertz Materials Analysis Center (THeMAC).
The vision is that THeMAC will address current and
future needs of fundamental and applied research in
materials science, physics, chemistry, life sciences,
defense, medicine, and ultra-fast communication.
The III-nitrides is a class of
materials that exhibit
extremely good highfrequency characteristics, in
addition to their outstanding
light emitting properties. A
project within the division
aims to develop the nitride material for high electron
mobility transistors, with applications in the next
generation high-speed data transmission systems.
The division has recently gained attention also
for graphene, in particular for a high temperature
fabrication process of graphene on SiC. The
exceptionally high carrier mobility in graphene
makes it a promising material for new devices
operating up to the terahertz frequency range.
Novel light sources
The optically efficient IIInitrides have enabled new
and energy efficient light
sources, such as LED-lamps
and blue lasers. Within the
division, there is a constant
activity for deepening the
understanding of the IIInitrides and for improving
the material quality in order
to further enhance its light
emitting performance.
One challenge tackled by the division is to develop a
III-nitride based light emitting material for deep
ultraviolet LEDs. The disinfecting properties of
ultraviolet light can be utilized for water cleaning.
SPECIAL EVENTS 2015
Career grant to Volodymyr Khranovskyy
Volodymyr received the Marie Sklodowska Curie
International Career Grant 2015 from the Swedish
Research Council (VR) for "Development of novel
two-dimensional functional oxide materials and their
integration into future 'green' electronics".
RESEARCH FUNDING
The turnover for research in our division was about
52.6 MSEK during the period 150101-151231,
including depreciation costs for equipment. The
major part of this budget comes from external
sources. The faculty support for research was about
7 MSEK for the year. External grants originate
mainly from the Swedish Research Council (VR),
the Knut and Alice Wallenberg Foundation (KAW),
the Swedish Strategic Research Foundation (SSF),
Swedish Energy Agency, Swedish Innovation
Agency (VINNOVA), European Defense Agency
(EDA/FMV) and EU. In addition there is a strong
support from and an intimate cooperation with
several industries, mainly Norstel AB, and Aixtron
AB, and with the Defense Research Institute FOI.
SELECTED RESEARCH PROJECTS
Major national projects
Isotope project – A major part of the KAW grant is
devoted to isotope enriched SiC, mainly for
improved thermal conductivity. Isotope enriched
SiC layers manifest a number of interesting
properties useful for scientific and industrial
applications. Among them is a very narrow spectral
linewidth, which enables detailed measurements of
defect centers. Another interesting phenomenon of
the enriched layers is that they exhibit significantly
higher thermal conductivity due to a reduced isotope
scattering process in the material. During 2015 we
have continued to investigate suitable process
conditions for SiC epitaxy from SiF4, which is one
of few precursors for isotope pure 28Si. By
combining experimental work with thermochemical
modeling we have managed to gain a much deeper
understanding of the growth chemistry, and how to
control the growth zone using this precursor.
PI: E. Janzén.
SiC – the Material for Energy-Saving Power
Electronics – started in 2012 and is funded by SSF
for four years. The project focuses on determining,
understanding and improving material related issues
in SiC epitaxy and gate dielectrics, which today are
the limiting factors for the SiC power device
technology. The project includes: (i) Understanding
and control of carrier lifetime limiting defects in
SiC material and devices, (ii) Characterization and
identification of device-critical epitaxial defects, (iii)
Investigating novel alternative gate dielectrics and
novel fabrication techniques, (iv) Develop on-axis
and/or low-off angle epitaxy for power device
applications and (v) Develop Cl-based epitaxy for
high growth rates.
Quantum chemical calculations of thermochemical
properties of halogenated Si and C species were
done to be able to make more precise calculations of
the adsorption of these species on SiC surfaces, and
of thermodynamic equilibrium conditions in the SiC-H-X systems (where X = Cl, Br or F). This work
has led to a deeper understanding of the growth
chemistry when using halogenated precursors, which
will help us to develop and improve the Cl-based
epitaxy process for high growth rates.
Detailed studies of the connection between deep
level defects and carrier lifetime in 4H-SiC have
been made by electrical and optical characterization
of hundreds of epitaxial layers. The overall
conclusion is that the carbon vacancy defect is the
dominant recombination center and limits the carrier
lifetime in 4H-SiC. PI: E. Janzén.
Bridging the terahertz gap – In this project, financed
by KAW, the Semiconductor Materials Division is
working in close collaboration with Chalmers
University in Gothenburg and KTH in Stockholm to
develop new electronics for telecommunication in
the terahertz frequency range. Excellent materials
for the active area of such devices are expected to be
indium nitride (InN) or indium rich indium gallium
nitride (InGaN). The Semiconductor Materials
Division is here focusing on understanding and
developing the synthesis of high quality, smooth InN
and InGaN layers by chemical vapor deposition. The
challenge lies in the huge lattice mismatch between
InN and the underlying layer, i.e. GaN, which often
leads to the formation of islands instead of flat layers
due to the strain relaxation. An alternative approach
for this is to steer the synthesis chemistry from the
gas phase to the surface by using an atomic layer
deposition approach where the In and N precursor
molecules are sequentially pulsed into the reactor to
saturate the surface with either In or N atoms. The
surface chemistry of the In-saturated surface may
break down the N precursor at low temperature,
allowing a low overall synthesis temperature. Such
idea has been proven viable for AlN, however, not
for InN to the best of our knowledge. The facility
was installed in 2015 and the process is under
development. Partner: E. Janzén.
High Power Microwave (HPM) is a research topic to
investigate how resistance GaN is towards high
power microwave. It is of importance when more of
the electronic components are integrated and can be
exposed to microwaves, for example close to an
antenna. Also, more reliable sensors can be
developed which could increase safety in air
transport. Since GaN is a wide band gap material, it
can handle large power at high temperature, which
would be the case if a GaN transistor would be
exposed to a HPM pulse. During the year,
intentional carbon doped GaN HEMT structures
have been evaluated for this purpose. The
advantages with these structures are a more confined
two dimensional electron gas as well as reduced
trapping effects in the GaN. The project is
collaboration with Chalmers (processing) and SAAB
(transistor evaluation). PI: E. Janzén.
THz ellipsometer - The core of a new Terahertz
Materials Analysis Center. A new rotating-analyzer
Terahertz (THz) ellipsometer operating in the range
of 0.1 – 1.0 THz and at variable angles of incidence
(28 – 90°) have been built in the Semiconductor
Materials Division. This unique instrument provides
quantitative information on the free charge carriers
(mobility, effective mass, density and sign) and THz
optical properties of complex and nanostructured
materials. We have demonstrated first successful
measurements of record high mobility in two
dimensional electron gas in AlGaN/GaN transistor
structures, conductivity of polymer thin films
(PEDOT) and in-situ determination of ambient
effects on the free-charge carrier properties of
monolayer graphene. PI: V. Darakchieva.
Our new THz ellipsometer setup.
European projects
OSIRIS – Optimal SIC substRates for Integrated
Microwave and Power CircuitS – is funded by the
ECSEL Joint Undertaking, aims at substantially
improve the cost effectiveness and performance of
gallium nitride (GaN) based components. Within the
project an innovative SiC material will be
developed, using single isotopic atoms for Si and C.
This material will offer thermal conductivity
improvements of up to 30%, as compared to regular
SiC. Such improvements are important for devices
dissipating a lot of power, in particular in SiC power
electronics and in microwave devices using GaN
high electron mobility transistors (HEMT) grown on
SiC semi-insulating substrates. For microwave
GaN/SiC HEMT this isotopic approach could create
a complete shift in the currently used substrate /
GaN epi-wafer technology.
The project, which started in May 2015, is funded
for 36 months. The partners in the project are III-V
lab (FR), Intraspec Technologies (FR), UMS France
(FR), CNRS (FR), Isosilicon AS (NO), Slovak
University of Technology in Bratislava (SK),
Ascatron AB (SE), Norstel AB (SE), and Linköping
University (SE).
Our role in the project is to develop and grow the
isotopic SiC material. Semi-insulating material for
GaN HEMT will be grown on on-axis substrates and
N+ material for PiN and Schottky diodes will be
grown on off-axis substrates. We will also grow the
AlGaN/GaN HEMT structures on the SI on-axis
material. We have successfully grown semiinsulating (resistivity > 1010 Ωcm) 4H-SiC material
on full 100 mm diameter on-axis wafers, without 3C
polytype inclusions.
PI: E. Janzén
Deputy coordinator: Ö. Danielsson
The Graphene flagship started in October 2013,
involving 126 academic and industrial research
groups in 17 European countries with an initial 30month-budget of 54 million euro. We are partner in
this project with focus on sublimation growth of
graphene on SiC. This initiative will help us to
implement our ideas how to scale up the production
of graphene. In 2014 the spin off company
Graphensic joint Graphene Flagship as associate
member. PI: R. Yakimova.
GraphOhm is an ongoing EU Joint Research Project
that started June 2013 on Quantum resistance
metrology based on graphene. Our contribution is
epitaxial graphene on SiC. R. Yakimova is
Researcher Excellence Grant (REG) holder in this
project.
We have also been providers of graphene on SiC in
the Nano-RF project, which is an ongoing
collaboration on Carbon Based Smart Systems For
wireless applications. Partner: R. Yakimova.
During 2015, we participated in a project within the
Marie Curie Actions Research Fellowship Program.
BIOSENSORS-AGRICULT is a project on
developing nanotechnology-based biosensors for
agriculture, with partners from France, Latvia,
Belarus and Ukraine. Four researchers where
involved in the staff exchange scheme of IFM
during 2015. Partner: R. Yakimova.
PUBLICATIONS
Research activities in this division during 2015 have
produced 75 articles published in well-recognized
international journals or peer reviewed conference
proceedings as well as 1 book chapter. During the
year, 13 invited talks were given by our staff at
international conferences or symposia. The
researchers of the division are well cited in
international journals with more than 29700 ISI
citations in total.
Details and highlights of the research work as well
as updated publication lists are available at our
website: www.ifm.liu.se/semicond.
SELECTED RESEARCH HIGHLIGHTS
Spectral signatures of high-symmetry quantum
dots
Quantum dots with at least three symmetry planes
provide a very promising route for the generation of
entangled photons for quantum information
applications. The great challenge to fabricate
nanoscopic dots of high symmetry is complicated by
the lack of characterization techniques able to
resolve small symmetry breaking. Here, we present
an approach for identifying and analyzing the
signatures of symmetry breaking in the optical
spectra of quantum dots.
‣K. F. Karlsson et al., New J. Physics 17 103017
(2015)
Cavity-enhanced optical Hall effect in twodimensional free charge carrier gases detected at
terahertz frequencies
Optical Hall effect
measurements at THz
frequencies allow the
determination of free charge
carrier concentration,
effective mass and mobility
at frequencies relevant for
future high frequency device
applications. Previous experimental approaches used
large external magnetic fields to produce measurable
optical Hall effect signals. Here, we demonstrate a
new avenue, which makes use of resonances in an
optical cavity thereby enhancing the signal
significantly. This allows the use of permanent
magnets and thereby simplifying the experiment
substantially.
‣S. Knight et al., Opt. Lett. 40, 2688 (2015)
Single photons from a hexagonal micro-pyramid
Single photon sources are both of fundamental
interest and a common condition for quantum
information applications. Here, we report on single
photon emission from an InGaN quantum dot
formed on the apex of a site-controlled hexagonal
GaN micropyramid. An approach to efficiently
suppress uncorrelated emission
from the pyramid base with a
processed metal film is
demonstrated to significantly
enhance the signal-tobackground ratio of the emission.
‣T. Jemsson et al., Nanotech. 26, 065702 (2015)
Brominated chemistry for chemical vapor
deposition of electronic grade SiC
We present a direct comparison between chlorinated
and brominated chemistry for chemical vapor
deposition (CVD) of SiC. Addition of chlorine to the
gas mixture reduces the time needed for growth of
SiC layers for electronic devices by a factor ten.
Addition of Cl enables formation of molecules with
Si-Cl bonds, which are stronger than Si-Si bonds
preventing formation of silicon clusters. By using
either HCl or HBr gas as additive we show that
brominated chemistry leads to the same high
material quality and control of material properties as
chlorinated chemistry.
‣M. Yazdanfar et al., Chem. Mater, 27, 793 (2015)
Light emission enhancement of ZnO films
There is of great importance to increase the
efficiency of light emitting devices. Here, we have
investigated a planar structure consisting of a thin
film of light emitting zinc oxide (ZnO) on a layer of
graphene on a silicon carbide substrate. It is
revealed, by optimizing the films thickness, the light
emission can be enhanced up to 650% for visible
and 360% for ultraviolet light. This phenomenon is
attributed to the formation of the nanosized cavity in
the light emitting medium, with graphene as back
reflector.
‣V. Khranovskyy et al., Carbon 99, 295 (2016)
Li induced effects in the electronic structure of
graphene grown on C-face SiC
In this study, the effects induced
in the electronic structure of Cface graphene are investigated
after depositing similar amounts
of Li and after heating at similar
temperatures as earlier done for Si-face graphene.
The essentially undoped graphene became electron
doped after Li deposition (1014 cm-2). Most of the Li
had intercalated after heating at 280"°C with a
significant reduction in the electron doping. Higher
temperatures led to desorption of Li from the sample
and at 1030"°C Li could no longer be detected.
‣L. I. Johansson et al., J. Vac. Sci. Technol., A 33,
061405 (2015)
Deposition of AlN doped by silicon: insights from
interaction between precursors
The incorporation of dopant and impurity atoms into
the material can be much affected by the reactions
between precursors in the gas-phase and boundary
layer in metal organic chemical vapor deposition
(MOCVD). We address aspects of the gas-phase
interaction between precursors underlying the
MOCVD of the ultimate wide-band-gap
semiconductor AlN doped by silicon, for which
there is no previous deliberation. Therefore, we
build a better understanding for the actual deposition
process of a modern-technology-relevant AlN
material for the development of deep ultraviolet
light-emitting diodes.
‣R.B. dos Santos et al., J. Phys. D: Appl. Phys. 48,
295104 (2015); R.B. dos Santos et al., Dalton
Transactions 44, 3356 (2015); A. Kakanakova et al.,
oral presentation at ICNS-11, Beijing, China
Structural properties of graphene grown by hightemperature sublimation on 4H-SiC
We report the growth of few layer graphene by hightemperature sublimation. The effect of growth
temperature on the graphene number of layers and
crystallite size is investigated and discussed in
relation to graphene coverage and thickness
homogeneity. The properties of the interface
between the C-face graphene and the SiC substrate
are identified, exhibiting an amorphous structure
composed of Si, O and C.
‣C. Bouhafs et al J. Appl. Phys. 117, 085701 (2015)
Stacking faults and conductivity reversal in InN
doped with Mg
Applications of InN in
advanced electronic devices
depend on achieving accurate
control of p-type doping in the
material. The only working
acceptor in InN is Mg.
However, if Mg concentration
in InN is increased above
certain limit, instead of having more free holes, InN
becomes again n-type conductive. Here, we
demonstrate that the switch from p- to n-type
conductivity in InN doped with Mg correlates with
the formation of stacking faults. We also determine
the structure of the stacking faults and their role for
the reduction of electrons mobility in highly Mg
doped InN.
‣Khromov et al., Appl. Phys. Lett. 106, 232102
(2015)
Optical properties and Zeeman spectroscopy of
Nb in SiC
Foreign atoms in a semiconducting material can
modify its properties, thus helping in achieving a
material with desired electrical or optical properties.
In this work, we explore in detail the optical
properties of Nb in several crystal modifications of
SiC and show that this element replaces two
neighboring atoms in the host lattice. Our results
demonstrate that Nb in SiC can be an important
candidate for implementing single photon emitters in
SiC for quantum communication applications.
‣A. Gällström et al., Phys. Rev. B 92, 075207
(2015)
Shallow donor in natural MoS2
Molybdenum disulphide
(MoS2) has recently emerged
as one of the most promising
two-dimensional
semiconductors for field-effect
transistors, integrated circuits,
phototransistors and sensors.
However, the donor that gives rise
to free carriers in the devices is still not known. In
this work we combine electron paramagnetic
resonance and density functional theory calculations,
and show that the shallow donor responsible for the
natural n-type conductivity in bulk MoS2 is rhenium
(Re) with an ionization energy of ~26 meV.
‣N.T. Son et al., Phys. Status Solidi RRL 9, 707
(2015)
Please visit www.ifm.liu.se/semicond for details and
more highlights.
STUDENT THESES
Doctoral theses
Thien Duc Tran: Electronic properties of intrinsic
defects and impurities in GaN
Ian Booker: Carrier lifetime relevant deep levels in
SiC
Chao Xia: Characterizations of as grown and
functionalized epitaxial graphene grown on SiC
surfaces
Xun Li: CVD solutions for new directions in SiC and
GaN epitaxy
Jr-Tai Chen: MOCVD growth of GaN-based high
electron mobility transistor structures
Andreas Gällström: Optical Characterization of
Deep Level Defects in SiC
Xuan Thang Trinh: Electron Paramagnetic
Resonance Studies of Point Defects in AlGaN and
SiC
Licentiate thesis
Tomas Jemsson: Time correlated single photon
spectroscopy on pyramidal quantum dots
!
Master theses
Yi-Chieh Chung: Transparent amphiphobic coatings
based on metal oxide films and nanocomposites
Jonathan Cygnaeus: Investigation of optimal Hillas
Parameter cuts on extensive air showers for
Cherenkov Telescope Array
Anna Håkansson: Probing graphene interfaces by
mediated bioelectrocatalysis
Kevin Maed: Graphene growth on SiC under Ar
ambient and H intercalation
Olof Norén: Epitaxial and bulk growth of cubic
silicon carbide on off-oriented 4H-silicon carbide
substrates
Andréa Nicollet: The influence of growth
temperature on CVD grown graphene on SiC
TEACHING
The division is very active in teaching and it has
responsibility of about 20 undergraduate and
graduate courses at IFM.
Undergraduate & master courses offered 2015
TFFM08 Experimental Physics (Son)
TFYY51 Engineering Project Y (Forsberg)
TFYY70 Physics of Cond. Mat. I (Virojanadara)
TFYA20 Surface Physics (Virojanadara)
TFYY57 Nanophysics (Paskov)
TFYA15 Models in Physics (Karlsson)
TFYY68 Mechanics (Hemmingsson)
TFYY55 Physics (Bergman)
PhD courses offered 2015
CAD of scientific use (Kordina)
Electrical characterization of semiconductors
(Sveinbjörnsson/Hemmingsson)
Nanoscale phenomena on surfaces and interfaces
(Yakimova/Michailov)
MOCVD (Kakanakova)
Semiconductor physics I (Darakchieva/Ivanov
/Karlsson)
Popular science activities
The Semiconductor Materials division arranged a
study visit by about 70 junior high school students
from Vadstena with help from the Biomolecular and
organic electronics division. The students spent 3
hours at IFM, learning about our research and its
relation to energy and sustainable development.
They participated in lectures about semiconductor
growth, energy saving power electronics and organic
solar cells. The youth also visited our research labs
with exciting hands-on experiments and
demonstrations. The event involved five senior
researchers and three PhD students.
Two high-school students spent one week with us
for semiconductor physics related project works.
Tove and Angelica, high-school students from
Birgittaskolan, simulated strain in GaN structures.
Our division also participated with exhibitions and
hands-on experiments at LiU’s Popular Science
Week, mainly targeting high-school students and
teachers. We demonstrated the effects of polarized
light in connection to our research on ellipsometry.
Fredrik Karlsson, Olle Kordina, and Philipp Kühne
visited Soltorgsgymnasiet in Borlänge and talked
about semiconductor light emitters, electricity usage
and SiC based power electronics, and graphene
respectively.
In total, more than 160 youths and 25 teachers
visited our division in order to learn more about
semiconductor materials during 2015.