Final answer:
Radiation recombination occurs when a photon is emitted, while nonradiative recombination involves the dissipation of energy as heat. Direct recombination is known as band-to-band recombination, typically found in direct-bandgap semiconductors where radiative recombination is dominant.
Step-by-step explanation:
The process is called radiation recombination when C. a photon is emitted. This occurs when, for example, protons and electrons recombine, resulting in the emission of radiation of different frequencies, which can be predicted by quantum mechanics.
The process is called nonradiative recombination when D. energy is dissipated as heat to the lattice. This is when the recombining charge carriers (electrons and holes) release their energy to the semiconductor lattice instead of emitting a photon.
Direct recombination is also called A. band-to-band recombination, and it is the transition of an electron from the conduction band directly into a hole in the valence band, emitting a photon in the process.
The kind of recombination that dominates in direct-bandgap semiconductors is radiative recombination due to the more efficient emission of photons.