Blocking Operation:

The on/off state of the device is controlled, as in a MOSFET, through the gate voltage V_G. If the voltage is applied to the gate contact, w.r.t. the emitter is less than the threshold voltage Vth then no MOSFET inversion layer is created and the device is turned off. While this is the case, any applied forward voltage shall fall across reversed biased junction J₂. The only current to flow will be a small leakage current. The breakdown voltage of this junction, therefore, finds out the forward breakdown voltage. It is an important factor, specifically for power devices where large voltages and currents are being dealt with. The breakdown voltage of one-sided junction is based on the doping of the lower-doped side of the junction that means the n- side. It is because the lower doping results in a wider depletion region and, therefore, a lower maximum electric field in the depletion region. This is for this reason that the n- drift region is doped much lighter than the p-type body region. The device which is being modelled is designed to have a breakdown voltage of 600V. The n+ buffer layer is frequently present to prevent the depletion region of junction J₂ from extending right to the p bipolar collector. The inclusion of this layer, though, drastically dropped the reverse blocking capability of the device as it is dependent on the breakdown voltage of junction J₃, that is reverse biased under reverse voltage conditions. The benefit of this buffer layer is            that it permits the thickness of the drift region to be dropped, therefore reducing on-state losses.