Si/SiGe heterojunction collector for low loss operation of Trench IGBT

A new concept of Insulated Gate Bipolar Transistor (IGBT) which uses a SiGe layer for the collector is proposed to suppress the tail-current which is a major cause of the power loss and limits the operation speed of the device. By using p ⁺ -SiGe layer for the collector of a n ⁺ pn ^- -type IGBTs, holes injected from the collector into the n ^- drift region during the on-state can be easily swept away to the SiGe collector when the device is cut-off. Two dimensional device simulation has been carried out for IGBTs which have trench gates. The device is assumed to be thined from the backside of the wafer to about 100μm and the SiGe collector layer is deposited on the back surface. Simulation results indicated that, the turn-off time is reduced from a few microseconds of the conventional Si collector device to a few hundred nanoseconds of the newly proposed SiGe collector device. Preliminary experiments using SiGe/Si diodes verify the fast reverse recovery. On the other hand, turn-on voltage loss is increased by the use of SiGe collector. We also demonstrate that this drawback can be minimized by adjusting the composition of SiGe and employing a Si-SiGe stripe-shaped collector.