Silicon Carbide and Related Materials 2004

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Authors: Konstantin V. Emtsev, Thomas Seyller, Lothar Ley, A. Tadich, L. Broekman, E. Huwald, J.D. Riley, R.C.G. Leckey
Abstract: We have investigated Si-rich reconstructions of 4H-SiC( 00 1 1 ) surfaces by means of low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), and angleresolved ultraviolet photoelectron spectroscopy (ARUPS). The reconstructions of 4H-SiC( 00 1 1 ) were prepared by annealing the sample at different temperatures in a flux of Si. Depending on the temperature different reconstructions were observed: c(2×2) at T=800°C, c(2×4) at T=840°C. Both reconstructions show strong similarities in the electronic structure.
Authors: Bharat Krishnan, Yaroslav Koshka
Abstract: Recombination-induced passivation (RIP) experiments were conducted on p-type SiC after plasma treatment in deuterium. Higher sensitivity of SIMS to deuterium allowed us to confirm that recombination-induced athermal migration of hydrogen is indeed a driving mechanism for the RIP phenomenon. Hydrogen (or deuterium) athermally migrates from the plasma-induced hydrogen- or deuterium-reach near-surface layer down to more than a micron in depth, which under certain conditions creates a sufficiently thick layer of the n-type conductivity in the originally ptype epilayer. Thermal admittance spectroscopy was applied to investigate the defect levels in the top portion of the bandgap of the RIP-induced n-type layer. A few different levels located close to the conduction band of the originally p-type material were investigated.
Authors: David Méndez, A. Aouni, Daniel Araújo, Etienne Bustarret, Gabriel Ferro, Yves Monteil
Abstract: The effect of the temperature at which the carbon source is introduced in the reactor on the early stages of the carbonization process is analyzed here. Three samples heated up to 1150°C with propane introduction temperatures (Tintro) of 725, 1030 and 1100°C are analyzed by transmission electron microscopy and attenuated total reflectance. The size of the SiC nuclei increases with Tintro. There is also an effect on the strain of the resulting carbonization layer. The electron diffraction pattern of the sample with the highest Tintro shows a fully relaxed 3C-SiC layer, while no evidence of SiC relaxation is present in low Tintro samples where the SiC islands seems to be pseudomorphic.
Authors: Kun Yuan Gao, Thomas Seyller, Konstantin V. Emtsev, Lothar Ley, Florin Ciobanu, Gerhard Pensl
Abstract: Atomic Layer Deposited Al2O3 films on hydrogen-terminated 6H-SiC(0001) were annealed in hydrogen atmosphere and characterized by admittance spectroscopy measurement and photoelectron spectroscopy (PES). The resultant density of interface trap (Dit) from admittance spectroscopy measurement is reduced near mid gap, but increases strongly towards the conduction band edge. Systematic PES measurements show that hydrogen annealing introduces Si4+ as a new component besides Si0 and Si+. Using different electron escape depths for photon electrons, depth profiling of Si in its different oxidation states was performed. The result indicates the formation of a top SiO2 layer and a rougher interfacial layer containing more Si+ and Si4+ which could be responsible for the strong increase of Dit just below the conduction band edge.
Authors: Valeri V. Afanas'ev, Florin Ciobanu, Sima Dimitrijev, Gerhard Pensl, Andre Stesmans
Abstract: Properties of defects encountered at the oxidized surfaces of silicon carbide (SiC) suggest their origin to be different from the dangling-bond-type defects commonly observed in the oxidized silicon. Among different models of these SiC/oxide interface states advanced during the past decade, two have received substantial experimental support. This first one is the “carbon cluster” model, which ascribes the traps with energy levels in the SiC bandgap to inclusions of elemental carbon formed during the SiC surface treatment and subsequent oxidation. The second model invokes intrinsic defects of SiO2 to account for the high density of interface states in the energy range close to the conduction band of SiC. Achievements in reducing the SiC/SiO2 defect density are discussed.
Authors: J.M. Knaup, Peter Deák, Adam Gali, Z. Hajnal, Thomas Frauenheim, Wolfgang J. Choyke
Abstract: The density of interface traps (Dit) in thermally oxidized SiC is unacceptably high for MOS device fabrication. The most severe problem is posed by the extremely high concentration of slow acceptor states near the conduction band edge of 4H-SiC. These states are attributed to near interface traps originating from (probably intrinsic) defects in the oxide. Here a systematic theoretical search is presented for possible defects in the oxide with an appropriate acceptor level. Supercell calculations using a hybrid functional approach (and resulting in a correct gap) on defects in alpha-quartz exclude the oxygen vacancy and the oxygen interstitial, as possible candidates. In contrast, these calculations predict interstitial silicon to have an acceptor level in the appropriate range. The carbon interstitial in silica has an acceptor level somewhat deeper than that. Occupation of these levels give rise to significant rearrangement of the environment, leading to a more extended defect structure.
Authors: Toshiharu Ohnuma, Hidekazu Tsuchida, Tamotsu Jikimoto, Atsumi Miyashita, Masahito Yoshikawa
Abstract: First-principles calculations for the abrupt SiO2/4H-SiC interfaces accounting for Si-Si bonding and Nitrogen atom termination have been performed. Interface states due to Si-Si bonds appear at the valence band edge. Interface states at the midgap vanish when N atom terminates the Si dangling bond, but the interface states arising from the Si-N bonds appear at the valence band edge at the same time.
Authors: João F. Justo, Cesar R.S. da Silva, I. Pereyra, Lucy V.C. Assali
Abstract: There is growing interest in understanding the properties of SiC-SiO2 interfaces, which can be formed by oxidation of silicon carbide surfaces. Here, we used variable cell shape ab initio molecular dynamics to investigate the structural and electronic properties of crystalline phases of silicon oxycarbide which could appear within such interfaces. We find that carbonoxygen single bonds may remain stable inside a silicon oxide matrix. For the Si2CO6 compound, there are at least two crystalline phases, both having large bulk modulii and wide bandgaps.
Authors: Charíya Virojanadara, Leif I. Johansson
Authors: Yasuto Hijikata, Hiroyuki Yaguchi, Sadafumi Yoshida, Y. Takata, K. Kobayashi, S. Shin, H. Nohira, Takeshi Hattori
Abstract: Thermal oxide films on SiC epitaxial (000-1) C-faces have been characterized by angle-resolved photoemission spectroscopy (AR-PES). The structure of wet oxide/SiC C-face interface was compared with that of dry oxide/SiC C-face, as well as that of dry oxide/SiC Si-face, in order to clarify why a MOS device of SiC C-face achieved good electrical properties. The improvement in electrical properties was confirmed by AR-PES measurements, evidencing differences in binding energy between SiC and the Si4+ components in Si2p and valence band region, and in binding energy between SiC and the CHx components in C1s. The reason for the improvement in electrical property of MOS devices by use of SiC C-face are discussed in terms of depth profiles of oxide films calculated from the AR-PES results.

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