MESFET drain current

In a MESFET, a Schottky gate contact is used to modulate the source-drain current. As shown in Figure 14-6b, in an //-channel MESFET, two n+ source and drain regions are connected to an //-type channel. The width of the depletion layer, and hence that of the channel, is modulated by the voltage applied to the Schottky gate. In a normally off device (Fig. 14-9 a), the channel is totally depleted at zero gate bias, whereas it is only partially depleted in a normally on device (Fig. 14-9 b). 

Figure 8.24 Typical output current—voltage characteristics of an arbitrary MESFET with an external pinch-off voltage of 2V. In two-piece models applicable to the cases where velocity saturation occurs, it is assumed that the mobility is constant in certain region of the channel under the gate toward the source and velocity is saturated in the rest. The boundary depends on the drain voltage and the gate dimension.

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