Transport characteristics of a symmetrically extended bipolar transistor

This work deals with a novel bipolar transistor structure consisting of a δp(B*)-δn(E)-δp(B) planar doping layer sequence embedded between two heavily doped n⁺ collector layers C* and C. Currents flowing in such a n⁺δpδnδpn⁺ structure are investigated under symmetrical bias conditions (V_EB=V_EB *, V_BC=V_B*C*). At V_EB>0 (forward bias), electrons, injected from the E layer over the B(B*) barrier, are collected in the C(C*) layer whereas holes, injected from B and B* over the E barrier, are collected in the respective counter-layer B* and B. In this structure, at V_BC=0, the difference between the total current emitted from E and the current collected in C and C* equals the electron-hole recombination current between E and B (E and B*). Accordingly, the current gain depends linearly on the recombination lifetime in the E-B(E-B*) region. At reasonable lifetimes (τ=1 μs) appreciable current gain values are obtained even at high B(B*) doping levels