Papers by Author: Michael E. Levinshtein

Abstract: In this paper, the radiation resistance of GaN and SiC is compared. The effect of the irradiation temperature on the carrier removal rate in both semiconductors during proton irradiation is considered. It was found that in GaN, as well as in SiC, the rate of carrier removal decreases with increasing irradiation temperature. The dependence of the GaN sample resistance on the radiation dose was also calculated based on a model previously proposed to describe a similar dependence for SiC. Based on the experimental data obtained, it is concluded that the processes of radiation compensation in GaN and SiC are similar.

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: In this paper, for the first time, we report 12 kV, 1 cm² SiC GTOs demonstrated with a novel negative bevel termination, which improves the breakdown voltage by >3.5 kV compared to the conventional multiple-zone Junction Termination Extension (JTE). The significant improvement in the blocking voltage was attributed to the elimination of the electrical field crowding in the periphery of the mesa with conventional JTE termination. This new termination has been used in both electrically and optically triggered SiC GTOs. An ultrafast turn-on speed of 70 ns has been measured on 12 kV, 1 cm² SiC light triggered GTOs.

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 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: Self-heating in high-voltage 4H-SiC PiN diodes has been studied experimentally and theoretically in dc and 8-ms single pulse modes. To simulate the self-heating, an electro-thermal model was used to calculate non-isothermal current-voltage characteristics at dc and current-time dependences at pulsed measurements. The dynamic instability of N-type was observed: the current decreases in spite of increasing of bias applied to the structure. At dc, irreversible diode degradation was found to occur at a current density of about 1700 A/cm2. Under a single current surge 8-ms pulse, the loss of thermal stability has been found at a current density of approximately 9000 A/cm2. Comparison of experimental data and simulations showed that the local temperature in the diode base at the end of the 8-ms, 9000-A/cm2 pulse reaches 2000 – 2300 K.

Abstract: Forward current-voltage (I-V) characteristics and non-equilibrium carrier lifetime, τ were measured in 4H-SiC pin diodes (10-kV rated, 100 μm base width). The τ value was found to be 3.7 μs at room temperature by measurements of open circuit voltage decay. To the best of the authors' knowledge, the above lifetime value is the highest reported for 4H-SiC. The forward voltage drops were measured to be 3.44 V at current density of 100 A/cm2 and 5.45 V at 1000 A/cm2 showing a very deep modulation of the blocking base by injected carriers. Diodes operated well at elevated temperatures up to 400oC. No essential forward degradation was detected after 300- A×min current stress at 400oC.

Abstract: Steady-state and transient characteristics of packaged 6-kV 4H-SiC junction diodes have been investigated in the temperature range Т = 300 – 773 К. Analysis of the forward current-voltage characteristics and reverse current recovery waveforms shows that the lifetimeτ of non-equilibrium carriers in the base of the diodes steadily increases with temperature across the entire temperature interval. The rise in τ and decrease in carrier mobilities and diffusion coefficients with increasing temperature nearly compensate each other as regards their effect on the differential resistance of the diode, Rd. As a result, Rd is virtually temperature independent. An appreciable modulation of the base resistance takes place at room temperature even at a relatively small current density j of 20 A/cm2. At T = 800 K and j = 20 A/cm2, a very deep level of the base modulation has been observed. The bulk reverse current is governed by carrier generation in the space-charge region via a trap with activation energy of 1.62 eV. The surface leakage current of packaged structures does not exceed 2×10-6 А at T = 773 K and a reverse bias of 300 V.