What is the process responsible for producing photons in a diode laser?

This is the process wherein the electron that has become overly excited is brought back to the valence band but this time in an empty spot. This empty spot is known as the hole. Take note that this can happen to all elements that contain electrons although the reason why it would happen may differ.

Do take note that the holes can be passed on by the atoms that make up the various molecules. Chemistry can be complicated but a proper understanding of this will give people better information about why some chemicals react that way or why some bonds cannot form.