InP-based double-heterostructure phototransistors with 135 GHz optical-gain cutoff frequency

A high-speed layer and process compatible phototransistor based on the authorsʹ InP-based double-heterostructure bipolar transistor technology is presented. By using only the base and a thin base-collector spacer as absorption layer, slow drifting holes in the collector layer are avoided. This results in record optical-gain cutoff frequencies of up to 135 GHz at the expense of intrinsic photodiode responsivity in a top-illuminated configuration.