Two-dimensional analysis for emitter ledge thickness of InGaP∕GaAs heterojunction bipolar transistors

In this letter, the influence of various emitter ledge thicknesses on the performances of InGaP∕GaAs heterojunction bipolar transistors is investigated based on the simulation and experimental data. The undesired surface channel phenomenon at the exposed base surface between base contact and emitter ledge is comprehensively analyzed. Moreover, improper thickness of emitter ledge passivations would cause serious surface recombination at the edge of emitter ledge. Therefore, the thickness of emitter ledge is a critical and should be carefully considered. From simulated and experimental results, the optimum emitter ledge thickness of InGaP∕GaAs heterojunction bipolar transistor is 100–200Å.