A self-consistent model for temperature and current distribution in abrupt heterojunction bipolar transistors

The thermal behavior of abrupt heterojunction bipolar transistors (HBTs) has been studied by coupling the thermionic-field-emission injection mechanism at the emitter-base heterojunction with the thermal-electric feedback phenomenon. The exact quantum mechanical injection mechanism rather than semiclassical WKB approximation is used in the present calculation to self-consistently calculate thermionic and tunneling components of current. Moreover, the total current and temperature are self-consistently evaluated by testing the convergence on both current and temperature. The calculation shows correctly that the degree of the partitioning between the thermionic and tunneling components are bias- as well as temperature-dependent. It is shown that even a single emitter finger can have a highly nonuniform temperature and current distribution across it, leading to current collapse phenomenon. At high power levels, this may give rise to current collapse phenomenon similar to that observed for the multifinger HBTs.