Aa. Grinberg et S. Luryi, ON THE THERMIONIC-DIFFUSION THEORY OF MINORITY TRANSPORT IN HETEROSTRUCTURE BIPOLAR-TRANSISTORS, I.E.E.E. transactions on electron devices, 40(5), 1993, pp. 859-866
Theory of the minority-carrier transport in heterostructure bipolar tr
ansistors (HBT) is reconsidered with a particular emphasis on the diff
erence between the cases of abrupt and graded emitter-base junctions a
nd the role in the former case of the quasi-Fermi level discontinuity
at the interface. Exact analytical formulas are derived for the curren
t-voltage characteristics of a double-heterojunction HBT, valid for ar
bitrary levels of injection and base doping, including the degenerate
case. The theory is applied to the static characterization of HBT whic
h compares the forward and reverse dependences I(C)(V(EB)) and I(E)(V(
CB)). It is shown that these characteristics coincide in the low-injec
tion limit, if both the emitter-base and the collector-base diodes hav
e ideality factors close to unity. The ratio of base cur rents in the
reverse and forward modes of operation can be used to determine the ab
rupt emitter-base conduction band discontinuity and estimate the scatt
ering length in the base.