Chapter 8Unipolar Power Switching Devices
8.1 Junction Field-Effect Transistors (JFETs)
We turn now to the first of the three-terminal power devices, the junction field-effect transistor, or JFET. As discussed in Section 7.1, three-terminal power switching devices emulate ideal switches, that is, they attempt to carry high current with minimal voltage drop in the on state and to block high voltages with minimal leakage current in the off state.
The basic operation of the JFET can be understood by reference to the schematic cross-section in Figure 8.1. The prototype n-channel JFET consists of two 
gate regions on either side of an n-type channel region. Each end of the channel is connected to an ohmic contact, designated the source and the drain. A depletion region exists at each gate-channel 
junction, and the width of this depletion region increases as the square root of the gate-to-channel voltage. Assuming a 
one-sided step junction, the depletion width can be written
where is the voltage difference (or Fermi level splitting) between the gate and the channel, is the channel ...
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