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The Semiconductor Materials Division develops and investigates materials for novel electronics with the main focus on silicon carbide (SiC), III-nitrides and graphene. The goal is to resolve fundamental and application-motivated issues of interest for Swedish and European industries. Read more...

Summary of activities by year
2015 | 2014 | 2013

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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 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 signatures of symmetry breaking in the optical spectra of quantum dots. Read more...

Single photons from a hexagonal micro-pyramid

Single photon sources are of interest 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 micro-pyramid. An approach to suppress uncorrelated emission from the pyramid base with a processed metal film is demonstrated to strongly enhance the signal-to-background ratio of the emission. Read more...

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. Read more...

Coherent control of single spins in silicon carbide

Electron spins that can be prepared in arbitrary states are the basic elements for quantum spintronics, such as quantum computing and nanoscale sensing. Here we demonstrate that missing atoms in a silicon carbide crystal can host single spins that are accessible by optical spectroscopy, with long coherence times even at room temperature. These results expand the interest of silicon carbide into the areas of quantum processing and integrated spintronics. Read more...

Assessing properties of mixed crystal structures in thin films

When grown under non-equilibrium conditions, crystals or thin films of technologically important materials may contain domains with different crystal structures. Here we develop and demonstrate nondestructive structural and optical methods to determine the ratio between different crystal phases and study the free-charge carrier and vibrational properties of mixed-phase films. Our approach allows us to establish the elusive properties of cubic InN. Read more...

Cubic Silicon Carbide (3C-SiC) approaches quality of commercial hexagonal SiC

Cubic silicon carbide (3C-SiC) is an attractive material for a number of semiconductor applications. However, due to its metastable nature, it is very challenging to grow with a crystalline quality similar to the one obtained in commercially available hexagonal SiC substrates. We introduce a novel approach to grow high crystalline quality 3C-SiC in a reproducible and controllable way. Thick (up to 1 mm) 3C-SiC layers grown using our approach could be used as seeding layers in bulk growth or in homoepitaxial growth for fabricating various device structures. Read more...

Resolving the doping limitations in aluminum gallium nitride

We achieve better understanding of complex growth phenomena underlying the deposition of the ultimate wide band gap semiconductor AlN and high-Al-content AlGaN alloys; and related doping by silicon (Si). We contribute essential new knowledge in explaining the notorious sharp increase of resistivity of Si-doped high-Al-content AlGaN by corroborating aspects of material growth with electron paramagnetic resonance measurements. Read more...

Graphene on the cubic silicon carbide

We applied a high temperature process to grow graphene on cubic silicon carbide (3C-SiC). No buffer layer was observed for the graphene grown on the (001) plane. The cubic symmetry of 3C-SiC leads to a lack of spontaneous polarization, as confirmed by the mild n-doping observed in graphene grown on the (111) plane. We demonstrated from different aspects that 3C-SiC is a good substrate for growth of epitaxial graphene. The 3C-SiC samples were grown in a well-controlled process for high crystalline quality without foreign polytype inclusions. Read more...

Study of Ag-dopants on the structural and optical properties of ZnO nanorods

Zinc oxide (ZnO) is a semiconductor material promising for optoelectronics due to its efficient light emitting properties. However, the key challenge that must be solved before ZnO can be used as a LED material is to make it so-called p-type. Substitution of some Zn atoms with silver (Ag) was recently proposed as an approach for obtaining p-type ZnO. Here we investigate the structural and optical properties of ZnO nanorods doped with Ag atoms. We demonstrate that Ag promotes the generation crystal defects and significantly modifies the optical spectrum of ZnO. These results can be of high importance for further progress on p-type ZnO. Read more...

Micropyramid emits antibunched photons in the ultraviolet

Linearly polarized photons emitted one by one form the basis for novel cryptography methods. Here we demonstrate that the photons emitted from a InGaN quantum dot grown on the apex of a GaN micropyramid exhibits single photon characteristics known as antibunching. Our experiments show that the quantum dot itself is a fast and close to perfect single photon emitter, but a superimposed background signal from the pyramid needs to be eliminated before utilization in polarization-based single photon applications. Read more...

High thermal stability quasi-free-standing graphene on silicon carbide through Platinum functionalization

Graphene grown on silicon carbide (SiC) provide solutions for high frequency electronics operating at high temperature. However, a major obstacle is that the electrons are substantially slowed down due to the first carbon layer formed on the SiC. Here we report on quasi-free-standing graphene layers with potentially fast electrons even at very high temperatures (1200°C), achieved by letting Platinum penetrate into the graphene-SiC interface. Read more...

Resonant ionization of shallow donors in electric field

Semiconductors are non-conductive at low temperatures because the electrons freeze in their lowest energy state at impurities. However, a sudden rise of the conductivity can occur at very high electric fields due to resonant ionization. We discuss this effect using a simplified model of the energy states of donor impurities, and our results are similar to the predictions of more advanced models and in very good agreement with our experiment. Read more...

Layer-number determination in graphene on SiC by reflectance mapping

Graphene attracts much attention due to its exceptional properties for future electronics. Growth of graphene on silicon carbide is promising for large-scale device-ready production. A significant parameter characterizing the quality of the grown material is the number of layers. Here we report a simple, handy and affordable optical approach for precise number-of-layers determination of graphene based on the reflected power of a laser beam. Read more...

Nano-resolution reveals the true nature of graphene

Graphene grown on the basal planes of silicon carbide is considered a most promising route for carbon-based nano-electronics. Two nonequivalent faces of silicon carbide can be used for this purpose, the carbon-face and the silicon-face. It was claimed that these two faces result in graphene with fundamentally different electronic properties. Here we reveal the actual similarity between graphene layers on the two faces by experiments on a nanometer scale. Moreover, the apparent difference previously seen in standard experiments can now be explained as the collective effect of microscopic grains of graphene formed on the carbon-face. Read more...

Plasma chemistry gets a boost from pulsed power

In the plasma state, free electrons and ions open up new low temperature reaction pathways, enabling thin film deposition on sensitive materials such as plastics. We recently presented the concept of high power pulsed plasma enhanced chemical vapor deposition (HiPP-PECVD), which use plasmas thousands of times more electron rich than conventional PECVD. By using carbon films as model system, we now show that more film is deposited from the same amount of acetylene and power when the power is delivered as high power pulses. This is attributed to a more efficient plasma chemistry due to the increased number of electrons. Read more...

Aluminum tunes the electronic properties of graphene on silicon carbide

Graphene has unique and superior electronic properties. It can be grown on silicon carbide by a graphitization process, enabling development of single layer graphene based electronics for high temperatures and high voltages. Aluminum is a commonly used contact material for electronics, but its stability on graphene has not been investigated. We show that a distinct change in the electronic properties of graphene occurs for temperatures above 350 °C, when aluminum penetrates into the graphene-silicon carbide interface. Our results evidence the importance of temperature of the graphene device, when using aluminum as contact material. Read more...

Understanding magnesium impurities in gallium nitride

Light-emitting diodes and laser diodes rely on positive charge carriers known as holes. These holes are provided by impurities, and for gallium nitride is magnesium the only impurity that is useful for this purpose. The exact properties of the magnesium impurity have long been controversial, partly due to instability of its spectral features. We are able to spectrally identify isolated magnesium impurities as well as impurities near faults in the stacking sequence of atomic layers in the gallium nitride crystal. These experimental results are in conflict with recent theoretical predictions of magnesium in gallium nitride. Read more...

Micro-pyramids offer route to polarization controlled photon emitters

We have developed a concept for emission of strongly polarized light with good control of the linear polarization direction. The light is generated by quantum dots formed on top of elongated hexagonal micro-pyramids. Our results could find use in applications such as energy-efficient backlighting of displays and polarized single-photon sources for quantum communication. Read more…

NEWS

Vanya Darakchieva is organizing the Swedish Terahertz Workshop. The meeting takes place March 14, in Planck, IFM.
 
Supaluck Amloy received a prestigious award for her thesis "Polarization resolved photoluminescence spectroscopy on III-nitride quantum dots" from the National Research Council of Thailand.
 
Jianwu Sun delivered his docent lecture about the world's energy consumption and how cubic silicon carbide is a promising semiconductor for direct conversion of solar energy into hydrogen.
 
New doctor in Semiconductor Physics
Thien Duc Tran successfully defended his PhD thesis Electronic properties of intrinsic defects and impurities in GaN.
 
New doctor in Semiconductor Physics
Ian Booker successfully defended his PhD thesis Carrier lifetime relevant deep levels in SiC.
 
New doctor in Semiconductor Physics
Chao Xia successfully defended his PhD thesis Characterizations of as grown and functionalized epitaxial graphene grown on SiC surfaces.
 
Career Grant to Volodymyr Khranovskyy
Volodymyr Khranovskyy has 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". Volodymyr will be supported by grants of SEK 5.5 million for a period of 3 years.
 
New PhD student
Yuchen Shi will work on the growth of cubic silicon carbide for hydrogen generation from solar driven water splitting with Mikael Syväjärvi and Jianwu Sun.
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Best Poster Award at ICNS
Chih-Wei Hsu and co-workers received the best poster award at the International Conference on Nitride Semiconductors 2015.
 

Vanya Darakchieva selected for SSF's Research Infrastructure Fellows
Vanya will be supported by grants of SEK 15 million for a period of 5 years for establishing a Center for terahertz materials analysis at Linköping University.
 

The first international symposium on SiC spintronics
Erik Janzén is organizing the first international symposium on SiC spintronics. The meeting takes place June 15-17, in Vadstena, Sweden.
 
New doctor in Semiconductor Physics
Xun Li successfully defended her PhD thesis CVD solutions for new directions in SiC and GaN epitaxy.
 
New project in flourescent SiC
Mikael Syväjärvi is a partner in a Danish project funded by Innovation Fund Denmark on a new type of white LED based on fluorescent SiC.
 
New doctor in Semiconductor Physics
Jr-Tai Chen (Ted) successfully defended his PhD thesis MOCVD growth of GaN-based high electron mobility transistor structures.
 
New conference in graphene
Mikael Syväjärvi is a co-organizer of the European Graphene Forum held 23-25 August in Stockholm, Sweden.
 
 
 

EVENTS

March 14 at 09:00 in Planch
The Swedish Terahertz workshop Terahertz Materials Analysis Center (THeMAC) Inauguration | Program

Semiconductor Materials' calendar

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RECENT PUBLICATIONS

October 9
K. F. Karlsson et al., "Spectral signatures of high-symmetry quantum dots and effects of
symmetry breaking"
New J. Phys. 17, 103017 (2015)

September 17
N. B. Sedrine et al., "Infrared dielectric functions and optical phonons of wurtzite YxAl1-xN"
J. Phys. D: Appl. Phys. 48, 415102 (2015)

September 22
R.R.Q. Freitas et al., "Topological insulating phases in two-dimensional bismuth-containing single layers preserved by hydrogenation"
J. Phys. Chem. C 119 23599 (2015)

June 8
S. Khromov et al., "Correlation between switching to n-type conductivity and structural defects in highly Mg-doped InN"
Appl. Phys. Lett. 106, 232102 (2015)

June 2
S. King et al., "Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies"
Opt. Lett. 40, 2688 (2015)

April 30
V. Jokubavicius et al., ”Single Domain 3C-SiC Growth on Off-Oriented 4H-SiC Substrates”
Cryst. Growth Des., 15 (6), 2940 (2015)

February 24
C. Bouhafs et al., "Structural properties and dielectric function of graphene grown by high-temperature sublimation on 4H-SiC(000-1)"
J. Appl. Phys. 117, 085701 (2015)

January 24
D. Nilsson et al., "On the behavior of silicon donor in conductive AlxGa1–xN (0.6 ≤ x ≤ 1)"
Phys. Status Solidi B 252 1306 (2015)

January 22
M. Yazdanfar et al., "Brominated Chemistry for Chemical Vapor Deposition of Electronic Grade SiC"
Chem. Mater. 27, 793 (2015)

January 19
T. Jemsson et al., "Polarized single photon emission and photon bunching from an InGaN quantum dot on a GaN micropyramid"
Nanotechnology 26, 065702 (2015)

January 6
R. B. dos Santos et al., "Feasibility of novel (H3C)nX(SiH3)3−n compounds (X = B, Al, Ga, In): structure, stability, reactivity, and Raman characterization from ab initio calculations"
Dalton Transactions 44, 3356 (2015)

December 1
D. J. Christle et al., "Isolated electron spins in silicon carbide with millisecond coherence times"
Nature Materials (2014)

M. Vidmann et al., "Coherent control of single spins in silicon carbide at room temperature"
Nature Materials (2014)

November 28
S. Schoche et al., “Free-charge carrier parameters of n-type, p-type and compensated InN:Mg determined by infrared spectroscopic ellipsometry ”
Thin Solid Films 571, 384 (2014)

November 20
S. Amloy et al., "Excitons and biexcitons in InGaN quantum dot like localization centers"
Nanotechnology 25, 495702 (2014)

November 14
M.-Y. Xie et al., "Assessing structural, free-charge carrier, and phonon properties of mixed-phase epitaxial films: The case of InN"
Phys. Rev. B 90, 195306 (2014)

October 23
X. T. Trinh et al., "Stable and metastable Si negative-U centers in AlGaN and AlN"
Appl. Phys. Lett. 105, 162106 (2014)

October 22
V. Jokubavicius et al., "Lateral Enlargement Growth Mechanism of 3C-SiC on Off-Oriented 4H-SiC Substrates"
Cryst. Growth Des. 14, 6514 (2014)

September 24
Z.  N, Urgessa et al., "Low temperature near band edge recombination dynamics in ZnO nanorods"
J. Appl. Phys. 116, 123506 (2014)

August 26
D. Nilsson et al., "Strain and morphology compliance during the intentional doping of high-Al-content AlGaN layers"
Appl. Phys. Lett. 105, 082106 (2014)

August 25
T. Jemsson et al., "Linearly polarized single photon antibunching from a site-controlled InGaN quantum dot"
Appl. Phys. Lett. 105, 081901 (2014)

August 5
M. Yazdanfar et al., "Finding the Optimum Chloride-Based Chemistry for Chemical Vapor Deposition of SiC"
ECS J. Solid State Sci. Technol. 3, 320 (2014)

July 7
I. G. Ivanov et al., "Resonant ionization of shallow donors in electric field"
Phys. Scr. 89, 085802 (2014)

June 24
I. D. Booker, et al., "Carrier Lifetime Controlling Defects Z1/2 and RB1 in Standard and Chlorinated Chemistry Grown 4H-SiC"
Cryst. Growth Des. 4 4104 (2014)

June 2
I. G. Ivanov et al., "Layer-number determination in graphene on SiC by reflectance mapping"
Carbon 77 492 (2014)

April 22
M.-Y. Xie et al., "Effect of Mg doping on the structural and free-charge carrier properties
of InN films"
J. Appl. Phys. 115, 163504 (2014)

March 4
D. Lundin et al., "Influence of pulse power amplitude on plasma properties and film deposition in high power pulsed plasma enhanced chemical vapor deposition"
J. Vac. Sci. Technol. A 32, 030602 (2014)

March 3
C. Xia et al., "Effects of Al on epitaxial graphene grown on 6H-SiC (0001)"
Mater. Res. Express 1 015606 (2014)

February 24
L. I. Johansson et al., "Multiple PI-bads and Bernal stacking of multilayer grapehene on C-face SiC, revealed by nano-Angle Resolved Photoemission"
Nature Sci. Rep. 4 4157 (2014)

February 7
B. Monemar et al., "Properties of the main Mg-related acceptors in GaN from optical and structural studies"
J. Appl. Phys. 115, 053507 (2014)

January 31
A. Lundskog et al., "Direct generation of linearly polarized photon emission with designated orientations from site-controlled InGaN quantum dots"
Light: Science & Applications 3, e139 (2014)

December 27
M. Yazdanfar et al., "
On the use of methane as a carbon precursor in Chemical Vapor Deposition of silicon carbide"
J. Cryst. Growth 390, 24 (2014)


Responsible for this page: Fredrik Karlsson
Last updated: 03/01/16