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  • 101.
    Nordell, Nils
    et al.
    Swedish Institute of Microelectronics, Sweden.
    Ojala, P.
    Vanberlo, W.H.
    Landgren, G.
    Linnarsson, Margareta K.
    KTH. Solid State Electronics.
    Diffusion of Zn and Mg in AlGaAs/GaAs structures grown by metalorganic vapor-phase epitaxy1990In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 67, no 2, p. 778-786Article in journal (Refereed)
    Abstract [en]

    The diffusion of thin, highly p-doped layers in AlGaAs/GaAs single- and double-heterostructures, grown by metalorganic vapor-phase epitaxy, was studied with C-V etch profiling and secondary ion mass spectroscopy. The effect of different post-growth heat treatments was investigated and diffusion coefficients for both magnesium and zinc were measured. It was found that Mg diffuses about twice as fast Zn and that the order of magnitude of the diffusion coefficient is 10-14 cm2 s-1 at 900 °C, the exact value being process and concentration dependent. A model based on the interstitial-substitutional diffusion mechanism with suitable kinetic limitations was successfully used to simulate the observed dopant concentration profiles.We also found an anomalous strong diffusion of zinc from GaAs into highly n-doped AlGaAs. Detailed results on this and other structures are presented and implications for optimal design of heterostructure devices such as bipolar transistors are discussed.

  • 102.
    Nordell, Nils
    et al.
    KTH.
    Schoner, A.
    Rottner, K.
    Persson, P. O. A.
    Wahab, Q.
    Hultman, L.
    Linnarsson, Margareta
    KTH.
    Olsson, E.
    Boron implantation and epitaxial regrowth studies of 6H SiC1998In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 27, no 7, p. 833-837Article in journal (Refereed)
    Abstract [en]

    Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2 x 10(16) cm(-3) and 2 x 10(18) cm(-3). Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700 degrees C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2 x 10(16) cm(-3), with a diffusion constant estimated to 1.3 x 10(-12) cm(2)s(-1). This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.

  • 103. Osterman, J
    et al.
    Anand, S
    Linnarsson, M
    KTH, School of Information and Communication Technology (ICT).
    Hallen, A
    Carrier concentrations in implanted and epitaxial 4H-SiC by scanning spreading resistance microscopy2002In: SILICON CARBIDE AND RELATED MATERIALS 2001, PTS 1 AND 2, PROCEEDINGS, 2002, Vol. 389-3, p. 663-666Conference paper (Refereed)
    Abstract [en]

    Free carrier distributions in 4H-SiC have been studied by scanning spreading resistance microscopy (SSRM). The SSRM signal is discussed in relation to the chemical impurity concentration measured by secondary ion mass spectrometry (SIMS). The method is demonstrated on a p-type Al epi-layer staircase structure with doping concentration ranging from 2x10(16)cm(-3) to 2x10(20) cm(-3) and an implanted acceptor dopant profile of shallow Al and deep B. The results of the epi-layer investigation are in good agreement with the macroscopic spreading resistance model R=rho/4r, and show a much higher dynamic range in 4H-SiC than conventional spreading resistance profiling. Measurements of the implantation profile reveal a resistance in the highly doped region (> 10(18) cm(-3)) of more than two orders of magnitude larger than that measured in the epi-layer with similar concentration. The observation may be attributed to remaining implantation-induced defects. The SSRM measurements also show a diffusion of B consistent with SIMS data. The investigation clearly demonstrates that the technique is a valuable method to determine high gradient carrier concentrations in p-type SiC, although the detailed mechanism of the spreading resistance current is presently not completely understood.

  • 104. Osterman, J
    et al.
    Hallen, A
    Anand, S
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Andersson, H
    Aberg, D
    Panknin, D
    Skorupa, W
    Techniques for depth profiling of dopants in 4H-SiC2001In: SILICON CARBIDE AND RELATED MATERIALS, ECSCRM2000, 2001, Vol. 353-356, p. 559-562Conference paper (Refereed)
    Abstract [en]

    Three different methods for measuring the depth distribution of dopants in 4H-SiC have been investigated: (I) Spreading Resistance profiling (SRP), (2) Scanning Capacitance Microscopy (SCM) and (3) Scanning Electron Microscopy (SEM). The investigated samples included p- and n-type epitaxial layers grown by vapor phase deposition with doping concentrations of 10(16)-10(20) cm(-3). Also p(+)n implanted profiles using a combination of Al and B multi-energy implantations were studied. All techniques were able to provide doping profiles qualitatively corresponding to secondary ion mass spectrometry (SIMS) data. The SRP results suggest a lower limit of the p-doping concentration below which the ohmic contact between the probe tip and sample becomes more Schottky-like. The magnitude of the SCM signal corresponds well to the chemical doping profile except in the depleted region surrounding the metallurgical junction of the p(+)n structure.

  • 105. Ou, H.
    et al.
    Ou, Y.
    Kamiyama, S.
    Kaiser, M.
    Wellmann, P.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Jokubavicius, V.
    Yakimova, R.
    Syväjärvi, M.
    Fluorescent SiC for white light-emitting diodes2012In: Asia Commun. Photonics Conf., 2012Conference paper (Refereed)
    Abstract [en]

    The strong photoluminescence from f-SiC was achieved after the optimization of the B and N concentrations. Surface nanostructures were successfully applied to enhance the extraction efficiency. f-SiC is a promising wavelength convertor for white LEDs.

  • 106. Ou, Haiyan
    et al.
    Ou, Yiyu
    Argyraki, Aikaterini
    Schimmel, Saskia
    Kaiser, Michl
    Wellmann, Peter
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Jokubavicius, Valdas
    Sun, Jianwu
    Liljedahl, Rickard
    Syväjärvi, Mikael
    Advances in wide bandgap SiC for optoelectronics2014In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 87, no 3, p. 58-Article in journal (Refereed)
    Abstract [en]

    Silicon carbide (SiC) has played a key role in power electronics thanks to its unique physical properties like wide bandgap, high breakdown field, etc. During the past decade, SiC is also becoming more and more active in optoelectronics thanks to the progress in materials growth and nanofabrication. This paper will review the advances in fluorescent SiC for white light-emitting diodes, covering the polycrystalline doped SiC source material growth, single crystalline epitaxy growth of fluorescent SiC, and nanofabrication of SiC to enhance the extraction efficiency for fluorescent SiC based white LEDs.

  • 107. Ou, Y.
    et al.
    Jokubavicius, V.
    Kaiser, M.
    Wellmann, P.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yakimova, R.
    Syväjärvi, M.
    Ou, H.
    Fabrication of broadband antireflective sub-wavelength structures on fluorescent SiC2013In: Materials Science Forum, 2013, p. 1024-1027Conference paper (Refereed)
    Abstract [en]

    Surface nanocones on 6H-SiC have been developed and demonstrated as an effective method of enhancing the light extraction efficiency from fluorescent SiC layers. The surface reflectance, measured from the opposite direction of light emission, over a broad bandwidth range is significantly suppressed from 20.5% to 1.0% after introducing the sub-wavelength structures. An omnidirectional light harvesting enhancement (>91%), is also achieved which promotes fluorescent SiC as a good candidate of wavelength converter for white light-emitting diodes

  • 108. Ou, Y.
    et al.
    Jokubavicius, V.
    Liu, C.
    Berg, R. W.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Kamiyama, S.
    Lu, Z.
    Yakimova, R.
    Syväjärvi, M.
    Ou, H.
    Photoluminescence and Raman spectroscopy characterization of boron-and nitrogen-doped 6H silicon carbide2012In: Silicon Carbide and Related Materials 2011, Trans Tech Publications Inc., 2012, Vol. 717-720, p. 233-236Conference paper (Refereed)
    Abstract [en]

    Nitrogen-boron doped 6H-SiC epilayers grown on low off-axis 6H-SiC substrates have been characterized by photoluminescence and Raman spectroscopy. The photoluminescence results show that a doping larger than 10 18 cm -3 is favorable to observe the luminescence and addition of nitrogen leads to an increased luminescence. A dopant concentration difference larger than 4×10 18 cm -3 is proposed to achieve intense photoluminescence. Raman spectroscopy further confirmed the doping type and concentrations for the samples. The results indicate that N-B doped SiC can serve as a good wavelength converter in white LEDs applications.

  • 109. Ou, Yiyu
    et al.
    Jokubavicius, Valdas
    Kamiyama, Satoshi
    Liu, Chuan
    Berg, Rolf W.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yakimova, Rositza
    Syvajarvi, Mikael
    Ou, Haiyan
    Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC2011In: Optical Materials Express, ISSN 2159-3930, Vol. 1, no 8, p. 1439-1446Article in journal (Refereed)
    Abstract [en]

    In the present work, we investigated donor-acceptor-pair emission in N-B doped fluorescent 6H-SiC, by means of photoluminescence, Raman spectroscopy, and angle-resolved photoluminescence. The photoluminescence results were interpreted by using a band diagram with Fermi-Dirac statistics. It is shown that with N and B concentrations in a range of 10(18) cm(-3) the samples exhibit the most intense luminescence when the concentration difference (n-type) is about 4.6 x 10(18) cm(-3). Raman spectroscopy studies further verified the doping type and concentrations for the samples. Furthermore, strong luminescence intensity in a large emission angle range was achieved from angle-resolved photoluminescence. The results indicate N-B doped fluorescent SiC as a good wavelength converter in white LEDs applications.

  • 110. Ou, Yiyu
    et al.
    Jokubavicius, Valdas
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yakimova, Rositza
    Syväjärvi, Mikael
    Ou, Haiyan
    Characterization of donor-acceptor-pair emission in fluorescent 6H-SiC2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T148, p. 014003-Article in journal (Refereed)
    Abstract [en]

    We investigated donor-acceptor-pair emission in N-B-doped 6H-SiC samples by using photoluminescence (PL) and angle-resolved PL. It is shown that n-type doping with concentrations larger than 10(18) cm(-3) is favorable for observing luminescence, and increasing nitrogen results in stronger luminescence. A dopant concentration difference greater than 4x10(18) cm(-3) is proposed to help achieve intense PL. Angular-dependent PL was observed that was attributed to the Fabry-Perot microcavity interference effect, and a strong luminescence intensity in a large emission angle range was also achieved. The results indicate that N-B-doped fluorescent SiC is a good wavelength converter in white LED applications.

  • 111. PASKA, ZF
    et al.
    HAGA, D
    WILLEN, B
    LINNARSSON, MK
    KTH, School of Information and Communication Technology (ICT).
    HIGHLY DOPED P+ REGIONS BY ZINC DIFFUSION UTILIZING METALORGANIC VAPOR-PHASE EPITAXY1992In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 60, p. 1594-1596Article in journal (Refereed)
    Abstract [en]

    Zinc-diffusion doping of GaAs using metalorganic vapor-phase epitaxy and DEZn as a dopant source is evaluated. The dependence of the diffusion profile on DEZn flow and diffusion time is presented. Typical zinc concentrations and depths obtained are 10(19)-10(21) cm-3 and 40-200 nm, respectively. The largest concentration gradient obtained in this manner was four orders of magnitude in 500 angstrom, and the highest zinc concentration was measured as 2 x 10(21) cm-3 at a sample surface. A heterojunction bipolar transistor fabricated using zinc-diffusion doping of the base and a regrown emitter showed an f(max) of 50 GHz.

  • 112. Persson, P. O. Å
    et al.
    Wahab, Q.
    Hultman, L.
    Nordell, Nils
    Industrial Microelectronics Center, Sweden.
    Schöner, A.
    Rottner, K.
    Olsson, E.
    Linnarsson, Margareta
    KTH, Superseded Departments, Electronics.
    Transmission electron microscopy investigation of defects in B-implanted 6H-SiC1998In: Silicon carbide, III-nitrides and related materials : ICSCIII-N'97: Proceedings of the 7th International Conference on Silicon Carbide, III-Nitrides and Related Materials, Stockholm, Swedem, september 1997, Trans Tech Publications Inc., 1998, Vol. 264-2, p. 413-416Conference paper (Refereed)
    Abstract [en]

    Silicon carbide is due to its wide bandgap, high saturated electron drift velocity, high electric breakdown field and high thermal conductivity a suitable material for electron devices operating at high temperatures, high powers and high frequencies.[1,2] In order for SIC to reach its full potential in device technology, doping is essential. Usually ion implantation is used for doping since diffusion is difficult in SiC. Boron is a useful material for implantation because of its low atomic weight and greater penetration depth than other accepters, yet very few studies have been conducted on B-implanted 6H-SiC. [3,4] In this investigation we have used transmission electron microscopy (TEM) to study structural defects that are found in B-implanted 6H-SiC layers.

  • 113. Platzer-Bjorkman, C.
    et al.
    Jani, S.
    Westlinder, J.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Scragg, J.
    Edoff, M.
    Diffusion of Fe and Na in co-evaporated Cu(In, Ga) Se-2 devices on steel substrates2013In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 535, p. 188-192Article in journal (Refereed)
    Abstract [en]

    In this work we study impurity diffusion into Cu(In, Ga) Se-2 from stainless steel substrates with and without Cr diffusion barriers using secondary ion mass spectrometry. For these substrate configurations we compare cases with and without adding NaF as a sodium precursor. A clear increase in impurity diffusion from the substrate is observed for samples with NaF. Devices made using our micro pilot line show the expected correlation between Fe content, Na content and efficiency, but the highest device efficiency obtained for steel substrates is still slightly below that of the glass substrate reference. We discuss reasons for the observed device performance.

  • 114. Primetzhofer, D.
    et al.
    Dentoni Litta, Eugenio
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Possnert, G.
    Ultra-thin film and interface analysis of high-k dielectric materials employing Time-Of-Flight Medium Energy Ion Scattering (TOF-MEIS)2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, p. 212-215Article in journal (Refereed)
    Abstract [en]

    We explore the potential of Time-Of-Flight Medium Energy Ion Scattering (TOF-MEIS) for thin film analysis and analyze possible difficulties in evaluation of experimental spectra. As a model system high-k material stacks made from ultra-thin films of HfO2 grown on a p-type Si (100) substrate with a 0.5 nm SiO2 interface layer have been investigated. By comparison of experimental spectra and computer simulations TOF-MEIS was employed to establish a depth profile of the films and thus obtaining information on stoichiometry and film quality. Nominal film thicknesses were in the range from 1.8 to 12.2 nm. A comparison of the results with those from other MEIS approaches is made. Issues regarding different combinations of composition and stopping power as well as the influence of channeling are discussed. As a supporting method Rutherford-Backscattering spectrometry (RBS) was employed to obtain the areal density of Hf atoms in the films.

  • 115. Schimmel, S.
    et al.
    Kaiser, M.
    Hens, P.
    Jokubavicius, V.
    Liljedahl, R.
    Sun, J. W.
    Yakimova, R.
    Ou, Y.
    Ou, H.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Wellmann, P.
    Syväjärvi, M.
    Step-flow growth of fluorescent 4H-SiC layers on 4 degree off-axis substrates2013In: Silicon Carbide and Related Materials 2012, Trans Tech Publications Inc., 2013, Vol. 740-742, p. 185-188Conference paper (Refereed)
    Abstract [en]

    Homoepitaxial layers of fluorescent 4H-SiC were grown on 4 degree off-axis substrates by sublimation epitaxy. Luminescence in the green spectral range was obtained by co-doping with nitrogen and boron utilizing donor-acceptor pair luminescence. This concept opens possibilities to explore green light emitting diodes using a new materials platform.

  • 116. Schimmel, S.
    et al.
    Kaiser, M.
    Jokubavicius, V.
    Ou, Y.
    Hens, P.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Sun, J.
    Liljedahl, R.
    Ou, H.
    Syväjärvi, M.
    Wellmann, P.
    The role of defects in fluorescent silicon carbide layers grown by sublimation epitaxy2014In: IOP Conference Series: Materials Science and Engineering, 2014, no 1Conference paper (Refereed)
    Abstract [en]

    Donor-acceptor co-doped SiC is a promising light converter for novel monolithic all-semiconductor white LEDs due to its broad-band donor-acceptor pair luminescence and potentially high internal quantum efficiency. Besides sufficiently high doping concentrations in an appropriate ratio yielding short radiative lifetimes, long nonradiative lifetimes are crucial for efficient light conversion. The impact of different types of defects is studied by characterizing fluorescent silicon carbide layers with regard to photoluminescence intensity, homogeneity and efficiency taking into account dislocation density and distribution. Different doping concentrations and variations in gas phase composition and pressure are investigated.

  • 117. Schleussner, S. M.
    et al.
    Törndahl, T.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zimmermann, U.
    Wätjen, T.
    Edoff, M.
    Development of gallium gradients in three-stage Cu(In,Ga)Se2 co-evaporation processes2012In: Progress in Photovoltaics, ISSN 1062-7995, E-ISSN 1099-159X, Vol. 20, no 3, p. 284-293Article in journal (Refereed)
    Abstract [en]

    We use secondary-ion mass spectrometry, X-ray diffraction and scanning electron microscopy to investigate the development over time of compositional gradients in Cu(In,Ga)Se2 thin films grown in three-stage co-evaporation processes and suggest a comprehensive model for the formation of the well-known notch structure. The model takes into account the need for compensating Cu diffusion by movement of group-III ions in order to remain on the quasi-binary tie line and indicates that the mobilities of In and Ga ions differ. Cu diffuses towards the back in the second stage and towards the front in the third, and this is the driving force for the movement of In and Ga. The [Ga]/[In?+?Ga] ratio then increases in the direction of the respective Cu movement because In has a higher mobility at process conditions than has Ga. Interdiffusion of In and Ga can be considerable in the (In,Ga)2Se3 film of the first stage, but seems largely to cease in Cu(In,Ga)Se2 and shows no signs of being boosted by the presence of a Cu2Se layer.

  • 118. Schoner, A
    et al.
    Karlsson, S
    Schmitt, T
    Nordell, N
    Linnarsson, M
    KTH, School of Information and Communication Technology (ICT).
    Hall effect investigations of 4H-SiC epitaxial layers grown on semi-insulating and conducting substrates1999In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 61-2, p. 389-394Article in journal (Refereed)
    Abstract [en]

    Nitrogen- and aluminum-doped 4H silicon carbide epitaxial layers were grown simultaneously on semi-insulating and conducting substrates. The layers were investigated by conventional van der Pauw Hall effect measurements and for comparison also with secondary ion mass spectrometry and capacitance voltage measurements. It was found, that the carrier concentration in the layers grown on conducting substrates were overestimated by the Hall effect measurement, which leads to an underestimation of the ionization energy of the main dopant, as compared to the layer grown on semi-insulating substrates. The difference can be explained by a two-layer Hall effect model. (C) 1999 Elsevier Science S.A. All rights reserved.

  • 119. Schoner, A
    et al.
    Rottner, K
    Nordell, N
    Linnarsson, Margareta
    Peppermuller, C
    Helbig, R
    Hydrogen incorporation in epitaxial layers of 4H- and 6H-silicon carbide grown by vapor-phase epitaxy1997In: Diamond and related materials, ISSN 0925-9635, E-ISSN 1879-0062, Vol. 6, p. 1293-1296Article in journal (Refereed)
    Abstract [en]

    The incorporation of hydrogen during vapor phase epitaxy was investigated using secondary ion mass spectroscopy, low temperature photoluminescence, and capacitance-voltage measurements. It was found that hydrogen incorporation is strongly dependent on the concentration of the acceptor dopants aluminum and boron, regardless of changes in the doping concentration caused by varying the concentration ratio between carbon and silicon or the dopant precursor flow. An electrical passivation of the acceptor dopants was found and could be reduced by annealing at temperatures above 1000 degrees C. At the same anneal temperature hydrogen-related photoluminescence was considerably reduced and the diffusion of hydrogen was detected. (C) 1997 Elsevier Science S.A.

  • 120. Scragg, Jonathan J.
    et al.
    Kubart, Tomas
    Wätjen, J. Timo
    Ericson, Tove
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Platzer-Björkman, Charlotte
    Effects of Back Contact Instability on Cu2ZnSnS4 Devices and Processes2013In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 25, no 15, p. 3162-3171Article in journal (Refereed)
    Abstract [en]

    Cu2ZnSnS4 (CZTS) is a promising material for thin film solar cells based on sustainable resources. This paper explores some consequences of the chemical instability between CZTS and the standard Mo "back contact" layer used in the solar cell. Chemical passivation of the back contact interface using titanium nitride (TiN) diffusion barriers, combined with variations in the CZTS annealing process, enables us to isolate the effects of back contact chemistry on the electrical properties of the CZTS layer that result from the synthesis, as determined by measurements on completed solar cells. It is found that instability in the back contact is responsible for large current losses in the finished solar cell, which can be distinguished from other losses that arise from instabilities in the surface of the CZTS layer during annealing. The TiN-passivated back contact is an effective barrier to sulfur atoms and therefore prevents reactions between CZTS and Mo. However, it also results in a high series resistance and thus a reduced fill factor in the solar cell. The need for high chalcogen pressure during CZTS annealing can be linked to suppression of the back contact reactions and could potentially be avoided if better inert back contacts were to be developed.

  • 121. Storasta, L
    et al.
    Magnusson, B
    Henry, A
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Bergman, J P
    Janzen, E
    Correlation between electrical and optical mapping of boron related complexes in 4H-SiC2002In: SILICON CARBIDE AND RELATED MATERIALS - 2002, 2002, Vol. 433-4, p. 423-426Conference paper (Refereed)
    Abstract [en]

    Boron related photoluminescence (PL) and capacitance transient spectroscopy (DLTS and MCTS) peaks have been investigated around SIMS craters. Enhancement of boron and hydrogen related PL was observed in the vicinity of the crater, whereas the concentration of electrically active boron as measured by MCTS has decreased considerably. Comparison of the boron MCTS peak behavior after electron and proton irradiation is presented. Possible defect models based on the obtained results are discussed.

  • 122. Suchodolskis, A.
    et al.
    Hallén, Anders.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnarsson, Margareta K
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Österman, John
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Karlsson, Ulf O.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Ion implantation damage annealing in 4H-SiC monitored by scanning spreading resistance microscopy2006In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 515, no 2, p. 611-614Article in journal (Refereed)
    Abstract [en]

    To obtain a better understanding of the damage annealing process and dopant defect incorporation and activation we have implanted epitaxially grown 4H-SiC layers with high doses of Al+ ions. Cross-sections of the samples are investigated by scanning spreading resistance microscopy (SSRM) using a commercial atomic force microscopy (AFM). The defects caused by the implanted ions compensate for the doping and decrease the charge carrier mobility. This causes the resistivity to increase in the as-implanted regions. The calculated profile of implanted ions is in good agreement with the measured ones and shows a skewed Gaussian shape. Implanted samples are annealed up to 400 degrees C. Despite these low annealing temperatures we observe a clear improvement of the sample conductivity in the asimplanted region.

  • 123. Sun, J. W.
    et al.
    Jokubavicius, V.
    Gao, L.
    Booker, I.
    Jansson, M.
    Liu, X. Y.
    Hofmann, J. P.
    Hensen, E. J. M.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT).
    Wellmann, P.
    Ramiro, I.
    Marti, A.
    Yakimova, R.
    Syväjärvi, M.
    Solar driven energy conversion applications based on 3C-SiC2016In: 16th International Conference on Silicon Carbide and Related Materials, ICSCRM 2015, Trans Tech Publications Ltd , 2016, p. 1028-1031Conference paper (Refereed)
    Abstract [en]

    There is a strong and growing worldwide research on exploring renewable energy resources. Solar energy is the most abundant, inexhaustible and clean energy source, but there are profound material challenges to capture, convert and store solar energy. In this work, we explore 3C-SiC as an attractive material towards solar-driven energy conversion applications: (i) Boron doped 3C-SiC as candidate for an intermediate band photovoltaic material, and (ii) 3C-SiC as a photoelectrode for solar-driven water splitting. Absorption spectrum of boron doped 3C-SiC shows a deep energy level at ~0.7 eV above the valence band edge. This indicates that boron doped 3C-SiC may be a good candidate as an intermediate band photovoltaic material, and that bulk like 3C-SiC can have sufficient quality to be a promising electrode for photoelectrochemical water splitting.

  • 124.
    Suvanam, Sethu Saveda
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Gulbinas, K.
    Usman, M.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Martin, David M.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Linnros, Jan
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Grivickas, V.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    4H-silicon carbide-dielectric interface recombination analysis using free carrier absorption2015In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 117, no 10, article id 105309Article in journal (Refereed)
    Abstract [en]

    In this paper, an alternative method to characterize the interface between 4H polytype of Silicon Carbide (4H-SiC) and passivating dielectric layers is established. The studies are made on dielectric-semiconductor test structures using Al2O3 as dielectric on 4H-SiC n-type epitaxial layers. Samples with different pre-and post-dielectric deposition preparations have been fabricated on epilayers of varying thicknesses. Effective lifetimes (tau(eff)) of all the samples were measured by an optical pump-probe method utilizing free carrier absorption (FCA) to analyse the influence of the 4H-SiC/dielectric interface on charge carrier recombination. The relative contribution to tau(eff) from the surfaces increases with decreasing epilayer thickness, and by analysing the data in combination with numerical modelling, it is possible to extract values of the surface recombination velocities (SRVs) for interfaces prepared in different ways. For instance, it is found that SRV for a standard cleaning procedure is 2 x 10(6) cm/s compared to a more elaborate RCA process, yielding a more than 50 times lower value of 3.5 x 10(4) cm/s. Furthermore, the density of interface traps (D-it) is extracted from capacitance-voltage (CV) measurements using the Terman method and a comparison is made between the SRV extracted from FCA measurements and D(it)s extracted from CV measurements on the same structures fabricated with metal contacts. It is observed that the SRV increase scales linearly with the increase in Dit. The strong qualitative correlation between FCA and CV data shows that FCA is a useful characterization technique, which can also yield more quantitative information about the charge carrier dynamics at the interface.

  • 125.
    Suvanam, Sethu Saveda
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Usman, M.
    KTH, School of Information and Communication Technology (ICT). Experimental Physics Laboratories, National Centre for Physics, Quaid-i-Azam University, Islamabad, Pakistan.
    Martin, D.
    Yazdi, Milad G.
    KTH, School of Information and Communication Technology (ICT).
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT).
    Tempez, A.
    Göthelid, Mats
    KTH, School of Information and Communication Technology (ICT).
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT).
    Improved interface and electrical properties of atomic layer deposited Al2O3/4H-SiC2018In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 433, p. 108-115Article in journal (Refereed)
    Abstract [en]

    In this paper we demonstrate a process optimization of atomic layer deposited Al2O3 on 4H-SiC resulting in an improved interface and electrical properties. For this purpose the samples have been treated with two pre deposition surface cleaning processes, namely CP1 and CP2. The former is a typical surface cleaning procedure used in SiC processing while the latter have an additional weak RCA1 cleaning step. In addition to the cleaning and deposition, the effects of post dielectric annealing (PDA) at various temperatures in N2O ambient have been investigated. Analyses by scanning electron microscopy show the presence of structural defects on the Al2O3 surface after annealing at 500 and 800 °C. These defects disappear after annealing at 1100 °C, possibly due to densification of the Al2O3 film. Interface analyses have been performed using X-ray photoelectron spectroscopy (XPS) and time-of-flight medium energy ion scattering (ToF MEIS). Both these measurements show the formation of an interfacial SiOx (0 < x < 2) layer for both the CP1 and CP2, displaying an increased thickness for higher temperatures. Furthermore, the quality of the sub-oxide interfacial layer was found to depend on the pre deposition cleaning. In conclusion, an improved interface with better electrical properties is shown for the CP2 sample annealed at 1100 °C, resulting in lower oxide charges, strongly reduced flatband voltage and leakage current, as well as higher breakdown voltage.

  • 126.
    Suvanam, Sethu Saveda
    et al.
    KTH, School of Information and Communication Technology (ICT), Elektronics, Integrated devices and circuits.
    Usman, Muhammed
    Martin, David
    Yazdi, Milad
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Götelid, Mats
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Elektronics, Integrated devices and circuits.
    Improved Interface and Electrical Properties of Atomic Layer Deposited Al2O3/4H-SiCManuscript (preprint) (Other academic)
  • 127. Svensson, B G
    et al.
    Hallen, A
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Kuznetsov, A Y
    Janson, M S
    Aberg, D
    Osterman, J
    Persson, P O A
    Hultman, L
    Storasta, L
    Carlsson, F H C
    Bergman, J P
    Jagadish, C
    Morvan, E
    Doping of silicon carbide by ion implantation2001In: SILICON CARBIDE AND RELATED MATERIALS, ECSCRM2000, 2001, Vol. 353-356, p. 549-554Conference paper (Refereed)
    Abstract [en]

    A brief survey is given of some recent results on doping of 4H- and 6H-SiC by ion implantation. The doses and energies used are between 10(9) and 10(15) cm(-2) and 100 keV and 5 MeV, respectively, and B and Al ions (p-type dopants) are predominantly studied. After low dose implantation (less than or equal to 10(10) cm(-2)) a strong compensation is observed in n-type samples and this holds irrespective of implantation temperature up to 600 degreesC. However, at higher doses (10(14)-10(15) Al/cm(2)) the rate of defect recombination (annihilation) increases substantially during hot implants (greater than or equal to 200 degreesC) and in these samples one type of structural defect dominates after past-implant annealing at 1700-2000 degreesC. The defect is identified as a dislocation loop composed of clustered interstitial atoms inserted on the basal plane in the hexagonal crystal structure. Finally, transient enhanced diffusion (TED) of ion-implanted boron in 4H-samples is discussed.

  • 128. Svensson, B G
    et al.
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Cardenas, J
    Petravic, M
    SIMS analysis of epitaxial layers for power- and micro-electronics1998In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 136, p. 1034-1039Article in journal (Refereed)
    Abstract [en]

    This paper gives an overview of recent secondary ion mass spectrometry (SIMS) studies of impurities and dopants in epitaxial layers of silicon and 6H silicon carbide (SiC). Detection limits in the 10(12) cm(-3) range are demonstrated for transition metal impurities like Ti in SiC. Hydrogen is found to be mobile in SiC at temperatures in excess of 600 degrees C despite strong trapping by defects and dopant atoms, and the effective diffusion coefficient exhibits an activation energy of similar to 3.5 eV. In epitaxially grown Si layers, containing Ge delta distributions, profile broadening and shift during sputtering by Ar+ ions are accurately described by recoil mixing. For O-2(divided by) ions oxide formation and surface swelling must also be considered. Further, at elevated sample temperature Ge is found to segregate out of the SiO2 surface layer formed during oxygen bombardment, consistent with a larger heat of oxide formation for Ge than Si and a high enough mobility in SiO2. (C) 1998 Elsevier Science B.V.

  • 129. Svensson, B.G.
    et al.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Wong-Leung, J.
    Janson, Martin S.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Kuznetsov, A. Yu.
    Alfieri, G.
    Grossner, U.
    Monakhov, E.V.
    Kortegaard Nielsen, Hanne
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Jagadish, C.
    Grillenberger, J.
    Ion implantation processing and related effects in SiC2006In: Silicon Carbide and Related Materials 2005, Pts 1 and 2 / [ed] Devaty, RP, 2006, Vol. 527-529, p. 781-786Conference paper (Refereed)
    Abstract [en]

    A brief survey is given of some recent progress regarding ion implantation processing and related effects in 4H- and 6H-SiC. Four topics are discussed; an empirical ion range distribution simulator, dynamic defect annealing during implantation, formation of highly p(+)-doped layers, and deactivation of N donors by ion-induced defects.

  • 130. SVENSSON, BG
    et al.
    LINNARSSON, MK
    KTH, School of Information and Communication Technology (ICT).
    MOHADJERI, B
    PETRAVIC, M
    WILLIAMS, JS
    SIMS AND DEPTH PROFILING OF SEMICONDUCTOR STRUCTURES1994In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 85, p. 363-369Article in journal (Refereed)
    Abstract [en]

    This paper reviews recent secondary ion mass spectrometry (SIMS) work on (i) isotope shifts in ion implantation profiles, (ii) dopant profiles in silicon and beam-induced oxidation and (iii) surface roughness and profile broadening of Al(x)Ga1-(x)As/GaAs superlattice structures. Comparison is made with other techniques, and, in particular, the issues of depth resolution and conversion between sputtering time and sample depth are emphasized.

  • 131. Syvajarvi, M
    et al.
    Yakimova, R
    Jacobsson, H
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Henry, A
    Janzen, E
    High growth rate epitaxy of thick 4H-SiC layers2000In: SILICON CARBIDE AND RELATED MATERIALS - 1999 PTS, 1 & 2, 2000, Vol. 338-3, p. 165-168Conference paper (Refereed)
    Abstract [en]

    Sublimation epitaxy for fabrication of thick 4H-SiC layers has been studied with respect to surface morphology, structural quality, and purity. The surface morphology of thick (50-100 mum) epilayers is smooth, even though the growth rate was 100 mum/h. These surfaces are obtained within a parameter window for morphological stability. The structural perfection is confirmed by high-resolution X-Ray diffraction measurements and the epilayer quality is improved compared with the substrate. The limitation in purity is dependent mainly on the purity of the SiC source material. The growth system purity, mainly graphite and Ta parts of the growth crucible, is also of major importance. Results from intentional doping for high-resistive, semi-insulating and p-type material are presented.

  • 132. Syvajarvi, M.
    et al.
    Yakimova, R.
    Kakanakova-Georgieva, A.
    Sridhara, S. G.
    Linnarsson, Margareta K.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Janzen, E.
    Study of nitrogen, aluminium and boron incorporation in SiC layers grown by sublimation epitaxy2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 237, p. 1230-1234Article in journal (Refereed)
    Abstract [en]

    Sublimation epitaxy is a growth technique viable for SiC epilayer fabrication since the method is technologically simple, the growth rate is high (up to 100 mum/h) and the as-grown surfaces arc very smooth. However, the remaining issues of purity and intentional doping control need to be studied and the behaviour understood before this method can be applied to device fabrication. We will show results of nitrogen, aluminium and boron incorporation in layers grown by sublimation epitaxy. The epilayers have been studied using electrical, secondary ion mass spectrometry and cathodoluminescence measurements as well as by low-temperature photoluminescence spectroscopy. Possible solutions to lower especially the nitrogen concentrations in epilayers are presented along with experimental results leading to epilayer net doping concentrations in the N-D - N-A similar to 10(15) cm(-3) range.

  • 133. Syväjärvi, M.
    et al.
    Ma, Q.
    Jokubavicius, V.
    Galeckas, A.
    Sun, J.
    Liu, X.
    Jansson, M.
    Wellmann, P.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Runde, P.
    Johansen, B. A.
    Thøgersen, A.
    Diplas, S.
    Carvalho, P. A.
    Løvvik, O. M.
    Wright, D. N.
    Azarov, A. Y.
    Svensson, B. G.
    Cubic silicon carbide as a potential photovoltaic material2016In: Solar Energy Materials and Solar Cells, ISSN 0927-0248, E-ISSN 1879-3398, Vol. 145, p. 104-108Article in journal (Refereed)
    Abstract [en]

    In this work we present a significant advancement in cubic silicon carbide (3C-SiC) growth in terms of crystal quality and domain size, and indicate its potential use in photovoltaics. To date, the use of 3C-SiC for photovoltaics has not been considered due to the band gap of 2.3 eV being too large for conventional solar cells. Doping of 3C-SiC with boron introduces an energy level of 0.7 eV above the valence band. Such energy level may form an intermediate band (IB) in the band gap. This IB concept has been presented in the literature to act as an energy ladder that allows absorption of sub-bandgap photons to generate extra electron-hole pairs and increase the efficiency of a solar cell. The main challenge with this concept is to find a materials system that could realize such efficient photovoltaic behavior. The 3C-SiC bandgap and boron energy level fits nicely into the concept, but has not been explored for an IB behavior. For a long time crystalline 3C-SiC has been challenging to grow due to its metastable nature. The material mainly consists of a large number of small domains if the 3C polytype is maintained. In our work a crystal growth process was realized by a new approach that is a combination of initial nucleation and step-flow growth. In the process, the domains that form initially extend laterally to make larger 3C-SiC domains, thus leading to a pronounced improvement in crystalline quality of 3C-SiC. In order to explore the feasibility of IB in 3C-SiC using boron, we have explored two routes of introducing boron impurities; ion implantation on un-doped samples and epitaxial growth on un-doped samples using pre-doped source material. The results show that 3C-SiC doped with boron is an optically active material, and thus is interesting to be further studied for IB behavior. For the ion implanted samples the crystal quality was maintained even after high implantation doses and subsequent annealing. The same was true for the samples grown with pre-doped source material, even with a high concentration of boron impurities. We present optical emission and absorption properties of as-grown and boron implanted 3C-SiC. The low-temperature photoluminescence spectra indicate the formation of optically active deep boron centers, which may be utilized for achieving an IB behavior at sufficiently high dopant concentrations. We also discuss the potential of boron doped 3C-SiC base material in a broader range of applications, such as in photovoltaics, biomarkers and hydrogen generation by splitting water.

  • 134. Syväjärvi, M.
    et al.
    Mueller, J.
    Sun, J. W.
    Grivickas, V.
    Ou, Y.
    Jokubavicius, V.
    Hens, P.
    Kaisr, M.
    Ariyawong, K.
    Gulbinas, K.
    Liljedahl, R.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Kamiyama, S.
    Wellmann, P.
    Spiecker, E.
    Ou, H.
    Fluorescent SiC as a new material for white LEDs2012In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T148, p. 014002-Article in journal (Refereed)
    Abstract [en]

    Current III-V-based white light-emitting diodes (LEDs) are available. However, their yellow phosphor converter is not efficient at high currents and includes rare-earth metals, which are becoming scarce. In this paper, we present the growth of a fluorescent silicon carbide material that is obtained by nitrogen and boron doping and that acts as a converter using a semiconductor. The luminescence is obtained at room temperature, and shows a broad luminescence band characteristic of donor-to-acceptor pair recombination. Photoluminescence intensities and carrier lifetimes reflect a sensitivity to nitrogen and boron concentrations. For an LED device, the growth needs to apply low-off-axis substrates. We show by ultra-high-resolution analytical transmission electron microscopy using aberration-corrected electrons that the growth mechanism can be stable and that there is a perfect epitaxial relation from the low-off-axis substrate and the doped layer even when there is step-bunching.

  • 135. Uneus, L
    et al.
    Nakagomi, S
    Linnarsson, M
    KTH, School of Information and Communication Technology (ICT).
    Janson, M S
    Svensson, B G
    Yakimova, R
    Syvajarvi, M
    Henry, A
    Janzen, E
    Ekedahl, L G
    Lunstrom, I
    Spetz, A L
    The effect of hydrogen diffusion in p- and n-type SiC Schottky diodes at high temperatures2002In: SILICON CARBIDE AND RELATED MATERIALS 2001, PTS 1 AND 2, PROCEEDINGS, 2002, Vol. 389-3, p. 1419-1422Conference paper (Refereed)
    Abstract [en]

    We present here the effect of a hydrogen anneal at 600degreesC for Schottky sensor devices based on n- and p-type 4H SiC. The devices have gate contacts of Ta/Pt, or TaSix/Pt. The catalytic metal gate dissociates hydrogen and thus promotes diffusion of hydrogen atoms into the SiC, where the atoms will trap or react with different impurities, defects or surface states. This will change parameters such as the carrier concentrations, the defect density of the material or the surface resistivity at the SiC/SiO2 interface. The current-voltage and the capacitance-voltage characteristics were measured before and after annealing in hydrogen and oxygen containing atmosphere, and the results show a reversible effect in the I-V characteristics.

  • 136.
    Usman, Muhammad
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Nazir, Aftab
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Aggerstam, Thomas
    KTH, School of Information and Communication Technology (ICT), Material Physics, Semiconductor Materials, HMA.
    Linnarsson, Margareta
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Electrical and structural characterization of ion implanted GaN2009In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 267, no 8-9, p. 1561-1563Article in journal (Refereed)
    Abstract [en]

    Ion implantation induced defects and their consequent electrical impact have been investigated. Unintentionally doped n-type gallium nitride was implanted with 100 keV Si+ and 300 keV Ar+ ions in a fluence range of 10(14)-10(15) ions/cm(2). The samples were characterized with Rutherford backscattering/Channeling method for damage buildup. Time of flight elastic recoil detection analysis was implied on the Si implanted samples to see the ion depth distribution. At implanted GaN samples were studied electrically with scanning spreading resistance microscopy. Our results show that an At fluence of 5 x 10(14) cm(-2) increases the resistance by five orders of magnitude to a maximum value. For the highest fluence, 6 x 10(15) cm(-2), the resistivity decreases by two orders of magnitude.

  • 137. Wikberg, J. M.
    et al.
    Knut, R.
    Audren, A.
    Ottosson, M.
    Linnarsson, M. K.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Karis, O.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Svedlindh, P.
    Annealing effects on structural and magnetic properties of Co implanted ZnO single crystals2011In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 109, no 8, p. 083918-Article in journal (Refereed)
    Abstract [en]

    Single crystals of ZnO were implanted with 100 keV-Co ions at room temperature with a fluence of 4.8 x 10(16) cm(-2) and subsequently annealed at different temperatures up to 800 degrees C. The samples were analyzed by Rutherford backscattering spectrometry, secondary ion mass spectrometry, X-ray diffraction, X-ray photoemission spectroscopy and magnetometry. The as-implanted Co:ZnO crystal shows a homogeneous distribution of Co in the near surface region of the crystal. Upon annealing, clear evidence of secondary phases is found. At the highest annealing temperature (800 degrees C) a ferromagnetic behavior is observed at room temperature with a coercive field of 120 Oe assigned mainly to metallic fcc Co nano-crystallites. We find that for the annealed samples, the temperature dependent magnetization cannot be explained within a model containing only a paramagnetic contribution due to well dispersed Co ions and a ferromagnetic contribution due to Co nano-crystallites, at least one more ferromagnetic contribution is needed for a consistent explanation of the experimental results.

  • 138. Wong-Leung, J.
    et al.
    Janson, Martin S.
    KTH, School of Information and Communication Technology (ICT).
    Kuznetsov, A.
    Svensson, B. G.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Jagadish, C.
    Cockayne, D. J. H.
    Ion implantation in 4H-SiC2008In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 266, no 8, p. 1367-1372Article in journal (Refereed)
    Abstract [en]

    Silicon carbide offers unique applications as a wide bandgap semiconductor. This paper reviews various aspects of ion implantation in 4H-SiC studied with a view to optimise ion implantation in silicon carbide. Al, P and Si ions with keV energies were used. Channelling effects were studied in both a-axis and c-axis crystals as a function of tilts along major orthogonal planes and off the major orthogonal planes. Major axes such as [0 0 0 1] and the [ 1 1 (2) over bar 0] and minor axis like the [1 1 (2) over bar 3] showed long channelling tails and optimum tilts for minimising channelling are recommended. TEM analyses of the samples showed the formation of (0 0 0 1) prismatic loops and the (1 1 (2) over bar 0) loops as well,in both a and c-cut crystals. We also note the presence of voids only in P implanted samples implanted with amorphising doses. The competing process between damage accumulation and dynamic annealing was studied by determining the critical temperature for the transition between crystalline and amorphous SiC and an activation energy of 1.3 eV is extracted.

  • 139. Wong-Leung, J.
    et al.
    Linnarsson, Margareta K.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Svensson, B. G.
    A comparison of extended defect formation induced by ion implantation in (0001) and (11(2)over-bar-0) 4H-SiC2003In: Physica. B, Condensed matter, ISSN 0921-4526, E-ISSN 1873-2135, Vol. 340, p. 132-136Article in journal (Refereed)
    Abstract [en]

    We study the effect of substrate orientation on defect formation in 4H-SiC. Both (1 1 (2) over bar 0) and (0 0 0 1) n-type 4H-SiC substrates were implanted with 400 keV P. The various samples, both as-implanted samples and annealed, were studied by Rutherford backscattering and channeling and transmission electron microscopy in an attempt to understand the damage evolution and defect structures resulting from different crystal orientations. Secondary ion mass spectrometry (SIMS) was performed for P elemental profiling before and after annealing. We observe a significantly different damage accumulation in the two directions with a broader amorphous layer formed in the c-cut crystal compared to the a-cut crystal. The annealing of the damage results in a range of different defects including dislocation loops and voids in both a-cut and c-cut crystals. The SIMS profiles show in some cases distinct differences between the two crystal directions.

  • 140. Wong-Leung, J.
    et al.
    Linnarsson, Margareta K.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Svensson, B. G.
    Cockayne, D. J. H.
    Ion-implantation-induced extended defect formation in (0001) and (11(2)over-bar0) 4H-SiC2005In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 71, no 16Article in journal (Refereed)
    Abstract [en]

    We study the effect of substrate orientation namely (11(2) over bar 0) and (0001) oriented crystals on defect formation in 4H-SiC. The microstructure of the various samples, as-implanted with P and annealed, were studied by Rutherford backscattering spectrometry and channeling and transmission electron microscopy in an attempt to understand the damage evolution and defect structures resulting from different crystal orientations and different implantation damage. The annealing of the damage results in a range of different defects including dislocation loops, voids and precipitates in both a-cut and c-cut crystals. For the c-cut crystals, we observe the formation of (a) Frank prismatic (0001) loops previously reported in implanted SiC, and (b) a second type of defects showing stacking fault contrast consistent with (i) pure Shockley partials and/or (ii) (0001) sheared interstitial defects bounded by a Shockley partial dislocation. A mechanism for the formation of the latter defects in SiC is proposed and the relative stacking fault energies of the proposed defects are estimated using calculated parameters for the axial next-nearest-neighbor Ising (ANNNI) spin model from the literature. For the a-cut crystal, we note the presence of two types of dislocation loops, with two habit planes, namely small dislocation loops located on the basal plane (0001) and large (11(2) over bar 0) prismatic loops. In addition, larger conglomerated loops which do not necessarily have a (11(2) over bar 0) habit plane and may be a larger variant of the (11(2) over bar 0) prismatic loops are also observed in the a-cut sample. Small precipitates are observed pinned to these loops. Elemental profiling of the implanted species before and after annealing by secondary ion mass spectrometry revealed a correlation between precipitation close to dislocation networks and the agglomeration of phosphorus at certain depths.

  • 141. Yakimova, R
    et al.
    Syvajarvi, M
    Lockowandt, C
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Radamson, H H
    Janzen, E
    Silicon carbide grown by liquid phase epitaxy in microgravity1998In: Journal of Materials Research, ISSN 0884-2914, E-ISSN 2044-5326, Vol. 13, p. 1812-1815Article in journal (Refereed)
    Abstract [en]

    6H and 4H polytype silicon carbide (SiC) layers have been grown on ground and under microgravity conditions by liquid phase epitaxy (LPE) from a solution of SiC in Si-Se solvent at 1750 degrees C. The effects of gravity on the growth parameters and material characteristiques have been studied. The growth rate, Sc incorporation, and the structural defects are modified in reduced gravity conditions, while the polytype reproduction of the substrate is not affected. The results obtained are intriguing as to further experiments providing objects for carrier lifetime measurements.

  • 142. YANG, BH
    et al.
    GISLASON, HP
    LINNARSSON, MARGARETA K.
    KTH, Superseded Departments, Electronics.
    LITHIUM PASSIVATION OF ZN AND CD ACCEPTORS IN P-TYPE GAAS1993In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 48, no 16, p. 12345-12348Article in journal (Refereed)
    Abstract [en]

    We report lithium passivation of the shallow acceptors Zn and Cd in p-type GaAs which we attribute to the formation of neutral Li-Zn and Li-Cd complexes. Similar to hydrogen, another group-I element, lithium strongly reduces the concentration of free holes when introduced into p-type GaAs. The passivation is inferred from an increase of both the hole mobility and the resisitivity throughout the bulk of the sample. It is observed most clearly for Li concentrations comparable to the shallow-acceptor concentration. In addition, compensation of shallow acceptors by randomly distributed donors is present in varying degree in the Li-diffused samples. Unlike hydrogenation of n-type GaAs, Li doping shows no evidence of neutralizing shallow donors in GaAs.

  • 143. Zhang, J.
    et al.
    Ellison, A.
    Danielsson, O.
    Linnarsson, Margareta K.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Henry, A.
    Janzen, E.
    Epitaxial growth of 4H SiC in a vertical hot-wall CVD reactor: Comparison between up- and down-flow orientations2002In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 241, no 4, p. 421-430Article in journal (Refereed)
    Abstract [en]

    The CVD growth of 4H SiC is investigated in a vertical hot-wall reactor in both up-flow (the chimney reactor) and down-flow (the inverted chimney) orientations. The growth rate and the nitrogen doping are studied for comparison. Under the investigated process conditions the growth mechanism is shown to be similar in these two reactor orientations. Only slight difference is observed in the temperature effect depending on the flow direction. Both reactor types have produced epilayers with high growth rates (10-35 mum/h) and low residual n-type doping (low 10(16) down to mid 10(13) cm(-3)) with comparable morphology. Dimensionless flow numbers are used to provide a qualitative analysis of the flow and heat transfer mechanisms in the vertical hot-wall system. Two-dimensional numerical simulation in a cylindrical geometry is conducted to demonstrate the flow and temperature profile with selected process parameters. Comparison of the experimental results in the chimney and the inverted chimney is performed to give insight into the fast epitaxial hot-wall growth.

  • 144. Zhang, J
    et al.
    Ellison, A
    Henry, A
    Linnarsson, M K
    KTH, School of Information and Communication Technology (ICT).
    Janzen, E
    Nitrogen impurity incorporation behavior in a chimney HTCVD process: pressure and temperature dependence1999In: Materials Science & Engineering: B. Solid-state Materials for Advanced Technology, ISSN 0921-5107, E-ISSN 1873-4944, Vol. 61-2, p. 151-154Article in journal (Refereed)
    Abstract [en]

    Experimental results are presented for residual nitrogen incorporation in both Si and C face 4H SiC epilayers using the high temperature chemical vapor deposition (HTCVD) process in a chimney reactor. The influence of total pressure, process temperature and input C/Si ratio on the residual nitrogen doping is studied. The results are further confirmed by intentional nitrogen doping experiments. Activation energies of 200 kcal/mol for Si face and 108 kcal/mol for C face samples are obtained for nitrogen incorporation. Possible incorporation mechanisms related to both surface and gas phase kinetics are discussed. (C) 1999 Elsevier Science S.A. All rights reserved.

  • 145. Zhang, J.
    et al.
    Ellison, A.
    Henry, A.
    Linnarsson, Margareta K.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Janzen, E.
    Nitrogen incorporation during 4H-SiC epitaxy in a chimney CVD reactor2001In: Journal of Crystal Growth, ISSN 0022-0248, E-ISSN 1873-5002, Vol. 226, no 03-feb, p. 267-276Article in journal (Refereed)
    Abstract [en]

    Nitrogen incorporation is studied during epitaxial chemical vapour deposition (CVD) of 4H-SiC in a vertical, hot-wall CVD reactor. The nitrogen doping dependencies on input C/Si ratio, growth temperature and process pressure are investigated under the process conditions leading to growth rates in the range of 15-30 mum/h. The nitrogen incorporation is observed to be a thermally activated process with a higher apparent activation energy for the Si-face than for the C-face. The site-competition principle is well followed at C/Si ratios higher than 0.3, whereas the nitrogen doping becomes less sensitive to the C/Si ratio on both the Si- and the C-faces at C/Si ratios below 0.3. The pressure has a strong effect on the nitrogen incorporation efficiency, allowing lower doping at the lower pressure. The influence of the growth parameters on the nitrogen incorporation is closely related both to the epitaxial growth mechanisms and to the surface kinetics on the different polarity SiC faces. The doping mechanisms are analysed taking into account the gas-phase chemistry and the surface kinetics.

123 101 - 145 of 145
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