Papers by Author: Natalja Sleptsuk

Abstract: In the present work, the kinetics of low-temperature annealing (400 °C) of 4H-SiC JBS diodes irradiated by electrons with an energy of 0.9 MeV and with a dose of 1E16 cm^-2 was studied. The dynamics of changes in I-V, C-V characteristics, as well as DLTS spectra are shown. In the course of the work, a thermal cycling effect was discovered, i.e., effect of multiple rapid cooling to the temperature of liquid nitrogen and heating of the samples. As a result of thermal cycling, the barrier capacity increases and the on-resistance (Rs) decreases. In the DLTS spectrum, a level of - 0.38 eV appears, absent in the as-irradiated diodes.

Abstract: The influence of 15 MeV proton irradiation temperatures (room temperature (RT) - 700 ° C) on the processes of defect formation in commercially available 4H-SiC JBS structures has been studied. It has been shown that the carrier removal rate does not depend on the irradiation temperature. At the same time, the irradiation temperature affected on the spectrum of introduced radiation defects. The conclusion about the possible influence of SiC crystal lattice structural defects on the processes of radiation defect formation has been made.

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.

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

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

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.

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.

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.

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.

Abstract: For more authentic comparison of Schottky parameters between combined sputter (Ti/Ni/Au) and diffusion welded (DW) Al contact and direct DW Al contact to SiC the forward current-voltage characteristics were measured at the temperature range 293-473 K on full-packed 0.3 cm2 Schottky diodes. Surprising fact was discovered that the temperature behaviour of parameters remains of the same character for both kind of contacts but for the combined sputter- DW samples the values of parameters is much closer in magnitude to sputter contacts. Apparently, chemical treatment before the DW process preserves untouched the contact surface layer formed by annealing of initial sputter metallization of the chips (e.g. Ni2Si, Ti3SiC2), and this layer serves as barrier during diffusion welding. In the second part of the work we give the results on long-term reliability testing where through the SiC Schottky diode with the DW Al contacts during 300 hr has been passed constant forward stabilized current of 100 A/cm2 density. The primary and final values of Uf for DW Schottky contact have not changed during the test.