Phototransistors are either tri-terminal (emitter, base and collector) or bi-terminal (emitter and collector) semiconductor devices which have a light-sensitive base region. Phototransistors and photodiodes can both be used for sensing light, but the phototransistor is more sensitive in view of the gain provided by the transistor. This makes phototransistors more suitable in a number of applications.
Phototransistors provide lower capacitance, high-speed response and low noise and low dark current along with excellent sensitivity. They are ideal for high-speed data transfer, light barriers, alarm systems, linear light measurement and more.