Impact of surface traps on downscaled InP/InGaAs DHBTs

The impact of surface traps on downscaled InP/InGaAs(P) double heterojunction bipolar transistors (DHBTs) is analyzed using accurate hydrodynamic 2D simulations, which are in good agreement with measurements. Traps on the surface of the base generate surface recombination reducing strongly the current gain. Traps on the emitter surface deplete this surface decreasing the effective active emitter area and consequently lowering the unity gain frequency f_T and the maximum oscillation frequency f_max for DHBTs with very small emitter widths of i.e. 200nm. This depletion length can be reduced by increasing the emitter doping. Traps on both surfaces induce a surface electron channel, which leads to leakage current. We show furthermore, that the influence of surface traps on the CML inverter gate delay is very small.