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...
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 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...
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...
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...
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) 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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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...
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…
Thien Duc Tran successfully defended his PhD thesis Electronic properties of intrinsic defects and impurities in GaN.
Ian Booker successfully defended his PhD thesis Carrier lifetime relevant deep levels in SiC.
Chao Xia successfully defended his PhD thesis Characterizations of as grown and functionalized epitaxial graphene grown on SiC surfaces.
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.
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.
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.
Erik Janzén is organizing the first international symposium on SiC spintronics. The meeting takes place June 15-17, in Vadstena, Sweden.
Xun Li successfully defended her PhD thesis CVD solutions for new directions in SiC and GaN epitaxy.
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.
Jr-Tai Chen (Ted) successfully defended his PhD thesis MOCVD growth of GaN-based high electron mobility transistor structures.
Mikael Syväjärvi is a co-organizer of the European Graphene Forum held 23-25 August in Stockholm, Sweden.
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Responsible for this page: Fredrik Karlsson
Last updated: 03/01/16