A numerical study of performance potential of Si/sub 1-x/Ge/sub x/ pseudomorphic heterojunction bipolar transistors

A two-dimensional drift-diffusion (DD) simulation and a one-dimensional hydrodynamic (HD) simulation are used to analyze the high-frequency performance of advanced Si BJTs and Si/sub 1-x/Ge/sub x/ pseudomorphic HBTs (PHBTs). The results on similar experimental devices are compared, and good agreement is observed for the Si device. Based on this agreement, it is estimated that equivalent Si/sub 1-x/Ge/sub x/ PHBTs should obtain an f/sub T/ of approximately=70 GHz. DD results give a maximum f/sub T/ of 60 GHz, but HD results suggest the higher figure of 70 GHz. Details of device operation are examined and sources of improved performance identified. Improved HD model parameters, most importantly the mobility, are discussed.