TRANSPORT CHARACTERISTICS OF A SYMMETRICALLY EXTENDED BIPOLAR-TRANSISTOR

This work deals with a novel bipolar transistor structure consisting of a deltap(B*) - deltan(E) - deltap(B) planar doping layer sequence embedded between two heavily doped n+ collector layers C* and C. Currents flowing in such a n+ deltapdeltandeltapn+ 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 (tau = 1 mus) appreciable current gain values are obtained even at high B (B*) doping levels.