Where should incident optical energy be directed in a photo diode?

In a photodiode, incident optical energy should ideally be directed toward the base-collector region. This is because the base-collector junction is where the photogenerated carriers (electrons and holes) are collected, leading to an electric current when light strikes the device.

When light hits the photodiode, it generates electron-hole pairs in the depletion region between the p-type and n-type semiconductor materials. These charge carriers are then swept into the base-collector region due to the electric field present in the depletion zone. By directing the optical energy toward this area, it maximizes the conversion of light into electrical signals, thus enhancing the photodiode’s sensitivity and performance.

In contrast to the choices, other areas such as the emitter region or substrate do not play a significant role in the collection of charge carriers from incident optical energy and may not effectively contribute to the photodiode's functionality.