🔍 Key Concepts

• Photodiode operation – how light energy creates charge carriers in a semiconductor junction • Relationship between light intensity and photocurrent in a photodiode • Effect of diode polarity/bias on whether the device is acting as a regular rectifier or a light sensor

💭 Think About

• Think about what happens inside the diode when more photons hit the junction: do we get more or fewer charge carriers available to move? • If a photodiode is wired correctly as a sensor, is its current mainly controlled by the applied voltage, or by the amount of light? • Ask yourself: in a typical light sensor circuit, when the light level increases, does the measuring instrument usually see the current go up, go down, or stay the same?

✅ Before You Answer

• Confirm that in normal photodiode mode the device is reverse-biased and behaves differently than an ordinary rectifying diode. • Recall that photocurrent is proportional to light intensity over a useful range of operation. • Make sure you are not confusing the photodiode with a photoresistor (LDR); think specifically about current through a diode junction.