The Frequency Characteristics Of The Sige Hbt For High Current Analytical Model

The high-frequency performance of SiGe base heterojunction bipolar transistors (HBT) at high current densities is studied in this thesis. A new one-dimensional analytic model of heterojunction barrier effect (HBE) in SiGe base HBT with an extended Ge into collector is proposed. Based on this model, the electron transit time, the current gain and the cutoff frequency are calculated. It shows that the onset of HBE can be delayed to higher current density when Ge is extended into collector. In addition, the onset current density of HBE increases when the depth of extended Ge increases. As a result, higher current gain and cutoff frequency at high current densities can be obtained in our model compared to the case of SiGe HBT without Ge into collector. It is also found that the collector current density at constant Base-Emitter Bias increases when Ge is extended into collector.The conclusions of this thesis are helpful to the design of SiGe base HBT at high current injection.