Gain enhancement in InAlAs/InGaAs heterojunction bipolar transistors using an emitter ledge

Improved gain was observed at low currents when a thin emitter ledge was incorporated into npn In0.52Al0.48As/In0.53Ga0.47As heterojunction bipolar transistors. A 40‐nm‐thick n‐In0.52Al0.48As emitter ledge resulted in over four times higher gain at low biases due to reduced surface recombination.