5 Frequency Properties

As mentioned in the Introduction, a high breakdown electric field allows the design of SiC thyristors with thinner and higher doped base layers than identically rated Si or GaAs structures. One can expect that the thinner base layers ensure much higher operating frequency of SiC thyristors. Indeed a very high operation frequency up to 600 kHz (at current density 30 A/cm ²) was realized in Ref. ^[54] for 6H-SiC thyristor. Prom practical point of view, however, the combination of high frequency and high current density is very important.

An operation frequency f ₀ of 1000 kHz for 400 V 4H-SiC thyristors at a current density j = 2700 A/cm ² and f ₀ = 500 kHz at j = 14000 A/cm ² were observed in Ref. ^[88]. For a 700 V SiC thyristor, f ₀ was 1000 kHz at j =480 A/cm ² and f ₀ was 500 kHz at j = 750 A/cm ^{2 [88]}. The frequency properties of the thyristors were investigated in a circuit of simple linear modulator (Fig. 29).

Fig. 29: Schematic of the experimental setup for high-frequency measurements ^[88]. C ₀ = 10 nF, R _L = 1 ? (ultra low-inductive resistor). The total pulse duration is about 100 ns

In this circuit the capacitor C ₀ is charged from an external bias source. The thyristor Th is switched-on by a gate...