Effect of surface recombination on the Early voltage in HBTs

摘要

The effect of surface recombination on the Early voltage inheterojunction bipolar transistors (HBTs) is presented. Calculationsare based by invoking the partitioning of the total current intothermionic and tunnelling components. The tunnelling current iscomputed by using an exact quantum mechanical calculation.Narrow-base HBTs are simulated by taking into account non-stationarytransport in the base. Surface recombination degrades the Earlyvoltage in a uniformly doped base. In an exponentially doped base ascaled-down base width modulation results in a higher Early voltage.At high base doping levels, the Early voltage is further degraded byneutral base recombination. Theoretical results are compared withexperimental data and the agreements are excellent.