Forward current-voltage characteristics of silicon carbide thyristors and diodes at high current densities

The lifetimes of minority carriers tau(n) have been measured for 4H-SiC n-p-n-p thyristors with breakover voltages of 400 V and 700 V at T = 300 K and T = 500 K. For structures of both types tau(n) approximate to 80 ns at T = 300 K, and tau(n) approximate to 280 ns at T = 500 K. The W/L ratios estimated from these data agree reasonably well with the values and temperature dependences of the critical charge densities measured in these structures earlier. (W is the width of the blocking p-base, L is the ambipolar diffusion length). With known tau(n) and contact resistivity R-c, forward current-voltage characteristics of the thyristors were calculated in the framework of a theory which takes into account the decrease of the emitter injection coefficient. The calculated and experimental results agree well over a wide range of current densities and temperatures. The related contributions of contact resistivity and non-ideality of the emitter junctions to the voltage drop across the thyristor structures are considered.