DECOUPLED ABSORPTION/GAIN REGION BIPOLAR PHOTOTRANSISTOR

摘要

A phototransistor capable of exhibiting a high gain-bandwidth product as well as fast carrier collection is presented. Phototransistors in accordance with the present invention include a transistor region whose base/ collector junction also serves as the PIN region of an integrated photodiode formed in a photodiode region of the device. The base layer is common to both the transistor region and the photodiode region; however, in the transistor region, the thickness of the base layer is thinner than in the photodiode region. By providing a base layer that is thinner in the transistor region than in the photodiode region, the base/collector junction depth is kept thin in the transistor region while remaining much deeper in the photodiode region. As a result, the transistor region is characterized by a short transit time, ensuring high ft, while the photodiode region is characterized by a large depleted carrier collection region having low capacitance.