Effect of surface recombination on the Early voltage in HBTs

摘要

The effect of surface recombination on the Early voltage in heterojunction bipolar transistors (HBTs) is presented. Calculations are based by invoking the partitioning of the total current into thermionic and tunnelling components. The tunnelling current is computed by using an exact quantum mechanical calculation. Narrow-base HBTs are simulated by taking into account non-stationary transport in the base. Surface recombination degrades the Early voltage in a uniformly doped base. In an exponentially doped base a scaled-down base width modulation results in a higher Early voltage. At high base doping levels, the Early voltage is further degraded by neutral base recombination. Theoretical results are compared with experimental data and the agreements are excellent.