In a diode, what process occurs when electrons recombine with holes?

When electrons recombine with holes in a diode, the process generates energy that is often emitted in the form of light. This phenomenon is particularly significant in light-emitting diodes (LEDs), where the recombination process is designed to produce visible light as a byproduct.

In a semiconductor diode, when an electron from the conduction band falls into a hole in the valence band, it transitions to a lower energy state. The energy difference between the two states is released, and depending on the material and the bandgap energy, this energy can manifest itself as light. This is known as electroluminescence.

While recombination can also produce heat as a secondary effect due to non-radiative recombination processes (where energy is lost as thermal energy instead of light), the primary and most notable outcome in many applications is the emission of light. Consequently, this makes the emission of light the defining characteristic of recombination in specific diode applications like LEDs, making it the correct response to the question.