Papers by Author: Pavel A. Ivanov

Abstract: Impact of 15 MeV proton irradiation on electrical characteristics and low frequency noise has been studied in high-power vertical 4H-SiC MOSFETs of 1.2 kV-class at doses 10¹² £ F £ 10¹⁴ cm^-2. The maximum value of the field-effect mobility µ_FЕ depends weakly on F up to F = 2×10¹³ cm^-2. At F = 4×10¹³ cm^-2, the character of the µ_FЕ(V_g) dependence changes radically. The maximum µ_FЕ decreases approximately threefold. The dose F_cr corresponding to the complete degradation of the device is about 10¹⁴ cm^-2. It can be estimated as F_cr» h_e/n₀, where h_e is the electron removal rate and n₀ is the initial electron concentration in the drift layer. In the entire frequency range of analysis f, gate voltages, and drain-source biases, the frequency dependence of the current spectral noise density S_I(f) follows the law S_I ~ 1/f. From the data of noise spectroscopy, the density of traps in the gate oxide N_tv has been estimated. In non-irradiated structures, N_tv » 5.4×10¹⁸ cm^-3eV^-1. At Ф = 6×10¹³ cm^-2, the N_tv value increases to N_tv » 7.2×10¹⁹cm^-3eV^-1. The non-monotonic behavior of the output current I_d and the level of low frequency noise on dose F has been demonstrated.

Abstract: The resistance of the BJT collector layer can be sharply reduced by the effective injection of minority carriers (holes) from base to collector. As a result, the voltage drop across the BJT becomes substantially lower. The conditions under which this process can occur are the short rise time and the high amplitude of the base pulse.

Abstract: Mesa-epitaxial 4H-SiC p⁺-p-n_o-n⁺-diodes were fabricated from commercial epitaxial wafers. Reverse recovery characteristics of the diodes were measured in pulse regimes to be relevant to operation of drift step recovery diodes (DSRDs) [1]. When injecting the minority carriers by forward current pulse followed by applying a reverse voltage pulse, the diodes are able to break the reverse current in a subnanosecond time (DSRD-mode). Different regimes of diode operation in DSRD-mode are investigated such as variable reverse voltage amplitude, forward current amplitude and duration, time delay between forward and reverse pulses.

Abstract: The 1/f noise has been investigated for the first time at 300 and 77 K in high-quality 4H-SiC Schottky diodes. It is shown that, that at 77 K, the dependence of the spectral noise density on current, S_I(I), differs fundamentally between the cases of the current flowing through the main part of the diode area with a comparatively high barrier and the current flowing through the nanosized patches with a comparatively low barrier.

Abstract: 4H-SiC MOSFETs with an epitaxial channel and NO postoxidation annealing have Si-like dependencies of noise on gate voltage. Such dependencies indicate that the density of the negatively charged oxide traps responsible for 1/f noise, N_tv, does not depend on the position of the Fermi level. The N_tv was found to be ~ 2×10¹⁹ cm^-3eV^-1. This value is considerably smaller than previously measured for transistors with ion implanted channels.

Abstract: We report on specific features of forward voltage degradation of 4H-SiC p-i-n diodes in the pulse mode. It is shown that pulse stresses with a pulse duration shorter than several milliseconds cause substantially smaller forward voltage drift in comparison with a dc stress with the same charge passed through the diodes and the same distribution of injected carriers. A self-recovery of the forward voltage is observed at room temperature.

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 this paper, very fast switch-off of high voltage 4H–SiC npn Bipolar Junction Transistors (BJTs) driven in deep saturation regime is reported. It is shown that the switch-off time can be as short as 4 ns if a reverse base current pulse is applied that provides forced minority carrier sweep out from the base.

Abstract: Low-frequency noise in 4H-SiC MOSFETs has been measured for the first time. At drain currents varying from deep subthreshold to strong inversion, the 1/f (flicker) noise dominated at frequencies 1 - 105 Hz. The dependence of relative spectral noise density, , on drain current Id (at a constant drain voltage Vd) differs qualitatively from that in Si MOSFETs. In Si MOSFETs, ~ 1/ in strong inversion, whereas tends to saturate in sub-threshold. In 4H-SiC MOSFETs under study, ~ 1/ over the whole range of currents from deep sub-threshold to strong inversion. Similar noise behavior is often observed in poly- or a-Si TFTs. The effective channel mobility in 4H-SiC MOSFETs, 3 - 7 cm2/Vs, is also as low as that in TFTs. Both noise behavior and transport properties of 4H-SiC MOSFETs are explained, analogously to TFTs, by a high density of localized states (bulk and interface) near the conduction band edge in the ion implanted p-well.

Abstract: Forward current-voltage characteristics of non-ideal Ti / 4H-SiC Schottky barriers with ideality factor n = 1.1 - 1.2 have been analyzed. The non-ideality is considered as a result of formation of a thin intermediate dielectric layer between the deposited titanium layer and 4H-SiC. Using experimental current-voltage characteristics, the electro-physical characteristics of Ti contacts such as the energy barrier height, the thickness of the intermediate layer and the energy distribution of the interface trap density are determined.