IGBT Modules - Technologies, Driver and Application (Second Edition) - page 47

, the greater the space-charge region will be and the smaller the resulting current
through the JFET.
Fig. 1.24
Layer design and circuit symbols of a JFET (not to scale) Metal oxide semiconductor field effect transistors
The most commonly used field effect transistor in power electronics applications is the
shows the circuit symbol and layer sequence of an n-channel
enhancement MOSFET
as it is typically used
. In addition to the vertical structure
shown here, there are lateral MOSFETs, but these are seldom found in power
applicationswith high blocking voltages.
In a self-blocking n-channel enhancement MOSFET, positive voltage at the gate
terminal in reference to the source terminal increases the conductivity of the p-doped
channel. This channel is located directly below the gate and connects the n-doped
source with the drain terminal. Due to the positive electrical field that forms at the gate,
the positive charge carriers below the gate in the p-doped zone are displaced, or in
other words the number of free electrons is increased, forming an n-conducting
inversion layer that creates the conducting channel between the source and drain
shows the channel with its specific range. Below, the creation of the
inversion channel is illustratedbyway of aMOS-capacitor.
As well as the vertical structure as an n-channel MOSFET, there are also p-channel MOSFETs. In theory, only
the doping is reversed.
TheMOSFET shownhere is also called vertical diffusedMOSFET (VDMOS) in the literature.
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