What is a photodiode?

• A. A device that stores energy
• B. A resistor used in circuits
• C. A semiconductor diode that, when exposed to light, generates a potential difference or changes its resistance
• D. A device that measures temperature

Answer: (C)

A photodiode is a semiconductor diode that responds to light by producing an electrical signal. When light shines on the PN junction, photons create electron-hole pairs. In reverse-bias operation, these carriers are quickly swept across the junction, generating a photocurrent that is proportional to the light intensity. Some photodiodes can also operate in photovoltaic mode, producing a small voltage with light without external bias. This light sensitivity and fast, linear response make it a detector, not a device that stores energy, a simple resistor, or a temperature sensor. So the description of a semiconductor diode that, when exposed to light, generates a potential difference or changes its resistance best matches a photodiode.