The branch-cut method and its application in two-dimensional device simulation

In the 2-D BJT simulation, the BJT device can be treated as two parts. One is the intrinsic (internal) BJT and the other is the extrinsic (parasitic) BJT. The extrinsic BJT effect is the factor that affects the current gain of the 2-D BJT model. To study the extrinsic BJT effect, we propose the branch-cut method to define and calculate the current components of the intrinsic and extrinsic BJTs. The current gain of the 2-D BJT model (β) will depend on the intrinsic base current ratio (I_B1/I_B), the current gain of the intrinsic BJT (β₁), and the current gain of the extrinsic BJT (<2). When the extrinsic BJT effect becomes stronger in the 2-D BJT simulation, IB₁/I_B will become smaller, and therefore β will decrease. In this paper, wo will study the 2-D BJT simulation with the different geometric parameters and the recessed-base structure. According to those simulation results, we can verify that β will decrease by the extrinsic BJT effect.