What is the main connection between electrical and optical processes in semiconductors?

The main connection between electrical and optical processes in semiconductors lies in the phenomenon of recombination and spontaneous emission. In semiconductors, when electrons from the conduction band recombine with holes in the valence band, they release energy. This energy can be emitted in the form of light, which is known as spontaneous emission. This process is fundamental to the operation of light-emitting diodes (LEDs) and semiconductor lasers, where the optical output is directly related to the electrical injection of charge carriers.

Recombination may occur due to thermal excitement or the injection of carriers through an external current. As these carriers recombine, they transition from a higher energy state to a lower energy state while emitting photons, thus bridging the gap between electrical energy (from current) and optical energy (light).

Other connections in the context of semiconductors focus on different mechanisms like absorption (which can lead to bandgap excitation) but do not directly link to the fundamental process of light generation as recombination does. The connections of diffusion to drift or transmission to reflection focus on transport or boundary phenomena rather than the interplay between electrical input and optical output, which is core to understanding semiconductor devices designed for opto-electronic applications.