Base doping profile effect in SiGe heterojunction bipolar transistors

The current gain and cut-off frequency performance in NPN Si/SiGe/Si double-heterojunction bipolar transistors (SiGe DHBTs) with two different base doping profiles (N_B) has been analyzed. The simulation results for conventional uniform-N_B SiGe DHBT are compared with the proposed SiGe drift-DHBT (DrDHBT) having N_B-ramp, while base Gummel number is kept constant in both the devices. The N_B ramp is controlled such that it minimizes the decelerating field component and a net accelerating field in quasi-neutral base of DrDHBT for minority electrons could be achieved. This increases the drift component of electron current in the quasi-neutral base, which gives rise to an increased current gain and improved cut-off frequency in DrDHBT depending on the value of drift-field parameter. Therefore, an optimized base doping profile could be implemented in place of uniform base doping for further improvement over uniform-N_B SiGe DHBTs.