Figure 8 shows the equivalent circuit of our structure (based on the equivalent circuit of the p-i-n diode) and a simplified circuit for the forward and reverse bias .
A fundamental property of the p-i-n diode is its i-region ambipolar carrier lifetime [tau], which represents the average time during which an electron-hole pair exists in the i-region of the diode .
Previously, it has been shown that to fabricate diodes with high breakdown voltage (more than 2000 V), highly resistive i-region of SiC p-i-n diodes needs to be created by epitaxial growth of thin SiC layer (free from micropipe defects) [14-16].
Developed SiC p-i-n diodes have fast switching time, and duration of the reverse recovery current is less than 10 ns with a breakdown voltage of 120-140 V.
But in our case, [L.sub.s] can be neglected as this small parasitic element has little effect on p-i-n diode performance below 1 MHz.
Forward biased p-i-n diode is a Current Controlled Resistor  and relationship between [R.sub.s] and [I.sub.f] can be described using
The reverse recovery characteristics of a 4H-SiC p-i-n diode under higher voltage and faster switching are investigated elsewhere  where it is shown that at a room temperature [tau] is -80 ns.
Caption: Figure 6: Equivalent circuit diagram of p-n junction with the intermediate layer of high resistance, constructed on the basis of an equivalent circuit of p-i-n diode .
Hiller, "Distortion in p-i-n Diode
Control Circuits," IEEE Transactions of Microwave Theory and Techniques, Vol.
Control devices and p-i-n diodes
are the subject of Chapter 8.