Study On Switching Characteristics Of 4H-SiC PiN Diodes

SiC PiN diodes, with high switching speed, large controllable power, low loss, are widely used in power switch circuits, amplitude limiter, phase shifter, anttenuator and microwave circuits.Numerical model has been setup with right parameters for 4H-SiC PiN. The DC I-V characteristics and switching characteristics are simulated accurately by ISE-TCAD. The turn-on voltage at a current density of 100A/cm2 is 3.0 V. The reverse breakdown voltage is 1335V. At 300K, when the diode is switched from forward current at 30mA to reverse voltage of 15 V, Qs and switching time are 0.052nC, 9.1ns.The influence of factors on switching characteristics are simulated, such as operational temperature, minority carrier lifetime, input forward current, reverse voltage and anode region doping concentration.With higher operational temperature, bigger input forward current and longer minority carrier life time, the reverse peak current and switching time increase.4H-SiC PiN switching diode with gradual changing doping in n-drift region is proposed in order to improve switching characteristics. The 6μm thick n-type drift region is divided into three regions and the doping concentration is 1×1014cm-3, 7×1015cm-3, 8×1017 cm-3. It is shown that there are about 30% increment in the softness parameters S and 10% shorter in switching time, compared with conventional structure. Simultaneously, as the conductivity modulation effect, the forward I-V characteristics are almost invariant. The reverse I-V characteristics has degenerated and the reverse breakdown voltage reduces by 220V, the reverse I-V characteristics are improved by adjusting the width of heavily doped region. Compared with 2 lays gradual changing doping, 3 lays gradual changing doping in n-drift region have more superior performance.