Papers by Keyword: Carbon Vacancy

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Authors: Hu Jun Jia, Yin Tang Yang, Chang Chun Chai
Abstract: Ohmic contact testing structures have been prepared on n type 4H-SiC layer with different multiple-layer metal, such as Ti/Ni/Au, Cr/Ni/Au and Ni/Ti/Au by magnetic sputter process. Special contact resistances about 10-6cm2 are achieved using TLM measurements. The composition of the alloy areas have been analyzed through XPS and AES, and the results show that the C vacancies induced by carbonides formation are important for ohmic contacts of Ti and Cr to SiC. However, the Ni/SiC structures need a relatively higher alloy temperature, so that the out diffusion of C atoms can offset the lack of Si in the top layer of SiC.
Authors: Hussein M. Ayedh, Roberta Nipoti, Anders Hallén, Bengt Gunnar Svensson
Abstract: The carbon vacancy (VC) is the major charge carrier lifetime limiting-defect in 4H-SiC epitaxial layers and it is readily formed during elevated heat treatments. Here we describe two ways for controlling the VC concentration in 4H-SiC epi-layer using different annealing procedures. One set of samples was subjected to high temperature processing at 1950 °C for 3 min, but then different cooling rates were applied. A significant reduction of the VC concentration was demonstrated by the slow cooling rate. In addition, elimination of the VC’s was also established by annealing a sample, containing high VC concentration, at 1500 °C for a sufficiently long time. Both procedures clearly demonstrate the need for maintaining thermodynamic equilibrium during cooling.
Authors: Ivana Capan, Tomislav Brodar, Takeshi Ohshima, Shinichiro Sato, Takahiro Makino, Željko Pastuovic, Rainer Siegele, Luka Snoj, Vadimir Radulović, José Coutinho, Vitor J.B. Torres, Kamel Demmouche
Abstract: We present a study of electrically active radiation-induced defects formed in 4H-SiC epitaxial layers following irradiation with fast neutrons, as well as 600 keV H+ and 2 MeV He++ ion implantations. We also look at electron emission energies and mechanisms of the carbon vacancy in 4H-SiC by means of first-principles modelling. Combining the relative stability of carbon vacancies at different sites with the relative amplitude of the observed Laplace-DLTS peaks, we were able to connect Z1 and Z2 to emissions from double negatively charged carbon vacancies located at the h- and k-sites, respectively.
Authors: L. Storasta, Isaho Kamata, Tomonori Nakamura, Hidekazu Tsuchida
Abstract: We have investigated the electrically active deep level defects in p- and n-type 4H-SiC after low energy electron irradiation. Intrinsic defects were created by irradiation with 200 keV electrons, with energy sufficient to move only the carbon atoms in SiC lattice. Defect spectra were compared between the p- and n-doped samples prepared under identical irradiation conditions. We probed both conduction and valence band sides of the band-gap by using capacitance transient techniques with electrical and optical trap filling. We have found that the defect spectrum in the p-type epilayers differs significantly from the n-type. The Z1/Z2, EH1 and EH3 electron traps which are usually present in irradiated n-type material could not be detected in p-type samples. An electron trap at 1.6 eV below the conduction band edge is present in both n- and p-type samples at the same energy position and with similar concentration, therefore it is probably related to the same type of defect. We have also found a new hole trap in p-type epilayers at energy EV + 0.66 eV.
Authors: Mary Ellen Zvanut, Won Woo Lee, Hai Yan Wang, W.C. Mitchel, William D. Mitchell
Abstract: The high resistivity of SiC required for many device applications is achieved by compensating residual donors or acceptors with vanadium or intrinsic defects. This work addresses the defect levels of substitutional vanadium and the positively charged carbon vacancy (VC +) in semiinsulating (SI) SiC. After reviewing the earlier studies related to both defects, the paper focuses on temperature-dependent Hall measurements and photo-induced electron paramagnetic resonance (EPR) experiments of 4H and 6H SI SiC. In vanadium-doped samples, a V3+/4+ level near Ec-1.1 eV (4H) and Ec-0.85 eV (6H) is estimated by a comparison of dark EPR spectra and the activation energy determined from the Hall data, assuming that vanadium controls the Fermi level. In high purity semiinsulating substrates, analysis of time-dependent and steady-state photo-EPR data suggests that the plus-to-neutral transition of the carbon vacancy involves a structural relaxation of about 0.6 eV.
Authors: Kazuki Yoshihara, Masashi Kato, Masaya Ichimura, Tomoaki Hatayama, Takeshi Ohshima
Abstract: We have characterized deep levels in as-grown and electron irradiated p-type 4H-SiC epitaxial layers by the current deep-level transient spectroscopy (I-DLTS) method. A part of the samples were irradiated with electrons in order to introduce defects. As a result, we found that electron irradiation to p-type 4H-SiC created complex defects including carbon vacancy or interstitial. Moreover, we found that observed deep levels are different between before and after annealing, and thus annealing may change structures of defects.
Authors: Augustinas Galeckas, Hussein M. Ayedh, J. Peder Bergman, Bengt Gunnar Svensson
Abstract: We address the key factors limiting charge carrier lifetime in 4H-SiC epilayers by demonstrating a viable method for eliminating carbon vacancy (VC) related Z1/2 lifetime killer sites and by introducing a novel approach in depth-resolved characterization of the carrier lifetimes across the epitaxial layer, which allows monitoring the efficacy of the proposed defect reduction scheme also exposing surface and interface recombination effects. We show that a moderate-temperature annealing conducted at 1500 °C for 6 hours under C-rich thermodynamic equilibrium conditions in effect eliminates carbon vacancies in epilayers to the levels below the detection limit (1011 cm-3) of DLTS measurements. The efficient reduction of VC-related Z1/2 sites upon thermal treatment is further proven by a significant increase of the minority carrier lifetime from 0.3µs to 1 µs, the upper limit apparently set by epilayer thickness dependent lifetime. Equally important is the extensive range of defect elimination as evidenced by consistently enhanced lifetime throughout entire 40 μm-thick epilayer, thus suggesting immediate practical implication as a lifetime control method suitable for variable thickness 4H-SiC epilayers.
Authors: Marianne E. Bathen, Hussein M. Ayedh, Lasse Vines, Ildiko Farkas, Erik Janzén, Bengt Gunnar Svensson
Abstract: The diffusion of the carbon vacancy (VC) in n-type 4H-SiC has been studied using Deep Level Transient Spectroscopy (DLTS). Samples grown along two different crystallographic planes, (0001) or c-cut and (11-20) or a-cut, have been utilized. The samples were implanted with 4.0 MeV C ions to generate VC’s and subsequently annealed at temperatures between 200 and 1500 °C. Following each annealing stage, concentration versus depth profiles of the VC were obtained. The VC is essentially immobile in both the c-cut and a-cut samples up to at least 1200 °C. The 1400 °C annealing stage, however, resulted in considerable migration, predominantly along the a-direction. Using half the difference in the Full Width at Half Maximum (FWHM) of the initial and diffused concentration profiles as a measure of the diffusion length, we deduced the diffusivity of the VC at 1400 °C to be approximately (3.8±1.1)×10-14 cm2/s along the c-axis and (4.1±1.2)×10-13 cm2/s along the a-axis, indicating a substantial anisotropy for the VC diffusion in 4H-SiC.
Authors: T. Umeda, Norio Morishita, Takeshi Ohshima, Hisayoshi Itoh, Junichi Isoya
Abstract: Carbon antisite-vacancy pair (CSiVC) is a fundamental defect in SiC, and is theoretically predicted to be very stable in p-type materials. However, this pair was found only in the form of a negatively charged state (i.e., the SI5 center = CSiVC −) in n-type and semi-insulating 4H-SiC, and yet, its presence has not been shown in p-type SiC. In this report, we present the first EPR observation on positively charged CSiVC pairs in p-type 4H-SiC. By carefully examining p-type samples after electron irradiation, we found a pair of new defects with C3v and C1h symmetries. They correspond to “c-axial” pairs (C3v) and “basal” pairs (C1h) of CSiVC +, respectively. The positively charged pairs are characterized by a strong 13C hyperfine interaction due to a dangling bond on a carbon antisite (CSi), which is successfully resolved for the c-axial pairs.
Authors: L. Storasta, Tetsuya Miyazawa, Hidekazu Tsuchida
Abstract: We have studied annealing of the main lifetime limiting defect Z1/2 in thick 4H-SiC epilayers by the application of carbon-implantation/annealing method. Examination of different implantation doses and annealing temperatures showed that finding the optimum conditions is crucial for obtaining carrier trap concentration below 1011 cm-3 in the whole 100 μm epilayer. The carrier lifetime increased from under 200 ns to over 1 μs at room temperature in the samples prepared by optimized carbon-implantation/annealing technique. Fabrication of pin diodes from the improved thick 4H-SiC epilayers confirmed the enhanced conductivity modulation and suitability of this technique for high-voltage bipolar SiC devices.
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