Insulated gate bipolar transistor or IGBT, is a solid state devices primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching.
The insulated gate bipolar transistor (IGBT) is a three terminal semiconductor device combines the benefits of both MOSFET and BJT.
So, an insulated gate bipolar transistor (IGBT) has input impedance like that of a MOSFET and low ON state power loss as in a BJT.
It is also called as metal oxide semiconductor insulated gate transistor (MOSIGT) and other name to this device are insulated gate transistor (IGT), conductivity modulated field effect transistor (COMFET).
Its constructed is similarly to a n-channel vertical construction power MOSFET except the n+ drain is replaced with a p+ collector layer, thus forming a vertical PNP bipolar junction transistor. This addition p+ region creates a cascade connection of a PNP bipolar junction transistor with the surface n channel MOSFET.