What happens to energy when electrons fall back down in a semiconductor?

When electrons in a semiconductor transition from a higher energy state in the conduction band back to a lower energy state in the valence band, they release energy. This energy release is approximately equal to the bandgap energy (Eg) of the semiconductor material involved. The bandgap energy represents the energy difference between the conduction band and the valence band.

During this process, the energy lost by the electrons can be emitted in the form of light (photons) in cases such as light-emitting diodes (LEDs) or laser diodes, or it can be dissipated as heat to the lattice of the semiconductor. The energy emitted corresponds closely to the bandgap energy, which is a fundamental property of the semiconductor material.

This understanding is critical when considering the behavior of semiconductors in devices, particularly in optics and electronics, where the bandgap energy directly influences the wavelengths of light emitted or absorbed.