Emitter size effect on current gain in fully self-aligned AlGaAs/GaAs HBT´s with AlGaAs surface passivation layer

The emitter size effect for fully self-aligned AlGaAs-GaAs heterojunction bipolar transistors (HBTs) with depleted AlGaAs passivation layers, in which the partially thinned AlGaAs emitter is self-aligned by using the dual sidewall process, is investigated. It is demonstrated that drastic improvement in the emitter size effect can be achieved with an AlGaAs passivation layer as small as 0.2 mu m in width, due to the surface recombination current reduction by a factor of 1/40 in the extrinsic base region. It has also been found that the base current is dominated by excess leakage current in the proton-implanted isolation region.<>