Papers by Author: Oleg Korolkov

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Authors: Alexander A. Lebedev, Klavdia S. Davydovskaya, Vitalii V. Kozlovski, Oleg Korolkov, Natalja Sleptsuk, Jana Toompuu
Abstract: In this paper investigation of degradation 4H SiC Schottky diodes parameters after irradiation by electrons with an energy of 0.9 MeV was doine. It was determined the carrier removal rate (Vd), which amounted to 0.07 - 0.09 cm-1. It is shown that the investigated Schottky diodes retained rectifying current-voltage characteristics of up to doses ~ 1017 cm-2. It is concluded that the radiation resistance of SiC Schottky diodes is much greater than the radiation resistance of Si p-i-n diodes with the same breakdown voltages
Authors: Oleg Korolkov, Toomas Rang, A. Syrkin, V. Dmitriev
Abstract: This paper is devoted to the results of a diffusion welding technique applied to solve the problem of packaging for large area SiC Schottky diodes. To supply low defect density substrates for fabrication of 0.3 cm2 Schottky diodes TDI defect-reducing technology was used. Diodes were fabricated on CVD grown low-doped 4H-SiC single epitaxial layer without edge termination. Double layer Ni-Au and triple layer Ti-Ni-Au sputter metallization were used for Schottky contacts fabrication. Non-rectifying backside contacts were provided by Ni-Au metallization. Diodes were tested on-wafer and delivered for dicing, and packaging. To decrease the parasitic spreading resistance the thickness of initial sputter metallization was increased by diffusion welded 30 μm metal foil. Combined thick and plane metal layers make it possible to perform the clamp mode package used in power electronics. This scheme of packaging ensures current takeoff from the whole contact area and allows operating temperatures up to 600°C. The forward current-voltage characteristics measured at 75 A measured for packaged diodes yields 250 A/cm2 (70A) at 1.9 V forward voltage. Reverse recovery time for packaged diodes was in the range of 29-36 ns.
Authors: Oleg Korolkov, Toomas Rang, Alexander Syrkin, Vladimir Dmitriev
Authors: Pavel A. Ivanov, Oleg Korolkov, Tat'yana P. Samsonova, Natalja Sleptsuk, Alexander S. Potapov, Jana Toompuu, Toomas Rang
Abstract: In the present paper, 4H-SiC JBS diodes with "boron" p–n junctions have been investigated by means of deep-level transient spectroscopy (DLTS). The sign of the DLTS signal for all the 4H-SiC diodes under study, was positive. The "anomaly" of the DLTS spectra measured is apparently connected with the properties of "boron" p–n junctions. In particular, is presented the role of deep D-centers in recompensation of donors in the JBS diodes.
Authors: Oleg Korolkov, Natalja Sleptsuk, Paul Annus, Raul Land, Toomas Rang
Abstract: In the present work we have considered the prototype of the high-voltage diode stack made on the basis of commercial SiC Schottky diodes. Implementation of vertical integration for four diode chips yielded stack with the reverse current of 25 μA under reverse voltage of 6 kV. The capacitance of the stack at zero bias is reduced more than three times in comparison with initial diodes. Reverse recovery time of the stack was 8.0 ns. This paper proposes a convenient analytical approach to the estimation of parameters of modular compositions with vertical architecture.
Authors: János Mizsei, Oleg Korolkov, Natalja Sleptsuk, Jana Toompuu, Toomas Rang
Abstract: This paper is a summary of the experimental study of deep levels in a SiC crystal lattice caused by diffusion welding (DW). Investigations were carried out by DLTS and Kelvin Probe methods. Investigations revealed that DLTS method is not applicable for identification of surface states. Research conducted by the Kelvin Probe method has shown an increase in the density of surface states after the diffusion welding from 2x1015 cm-2 to 3.5x1016 cm-2.
Authors: Oleg Korolkov, Natalja Sleptsuk, Alla A. Sitnikova, Mart Viljus, Toomas Rang
Abstract: In our early analytic reports [1,2] has been made the supposition that during the diffusion welding (DW) in subcontact area of SiC is formed the intermediate amorphous layer. In the present work are given the first results of transmission electron microscopy (TEM) and electron diffraction investigations of subcontact layers in n0-n- 4H-SiC. TEM examinations show that the boundary between aluminium and silicon carbide looks like stripy interface layer of ~ 25 nm thickness. This is the evidence that during diffusion welding in subcontact surface layer of SiC the shear micro deformations have been taking place and due to this process the plane inclusions of small-grained phase have been appeared. The image of contact area obtained in diffracted SiC rays (dark field) apparently confirms that stripy zone belongs to silicon carbide because the aluminium (black zone) fell out of contrast. Diffraction picture obtained from bulk zone of silicon carbide looks like monocrystallin, but the micro diffraction pattern obtained from the subcontact (stripy zone) gives a lot of concentric rings, that makes evidential the fact of existence of small-grained inclusions. Deciphering of this electron-diffraction pattern reveals the presence of such elements as residue SiC, Al, Si, as well as inclusions of graphite.
Authors: Oleg Korolkov, Raul Land, Jana Toompuu, Natalja Sleptsuk, Toomas Rang
Abstract: In the present work, the prototype of a voltage multiplier represented as the diffusion-welded stack is presented. Two options of multiplier prototypes are considered: the scheme with external capacitors and the multiplier of the vertical composition using the diode's own capacitance. Oscillograms of input and output signals for both multiplier composition are presented.
Authors: Oleg Korolkov, Vitalii V. Kozlovski, Alexander A. Lebedev, Raul Land, Natalja Sleptsuk, Jana Toompuu, Toomas Rang
Abstract: We considered the prototype of a SiC Schottky diode Rectifier Bridge made on the basis of commercial SiC Schottky diodes by diffusion welding (DW). Vertical integration for four diode chips in combination with molybdenum electrodes can improve the overall weight and dimensions of the module performance and increase device durability to radiation exposure. Our DW prototype, in contrast to commercial bridges, completely preserved the initial characteristics after irradiation by electrons with an energy of 0.9 MeV and density of 3 x 1016 cm-2
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