SOLUTION

Electron-hole pairs are produced by recombination.

Detailed Explanation

⇒ An intrinsic semiconductor is a semiconductor crystal in which electrical conduction arises due to thermally excited electrons and holes.

⇒  In semiconductors, a single event of covalent bond breaking leads to the generation of two charge carriers, an electron in the conduction band and a hole in the valence band. The process may be represented as

Covalent Bond + Thermal Energy ⇒ (Electron + Hole)Pairs

⇒  As electron and hole are produced simultaneously, the process is called electron-hole pair generation.

⇒ In the process of generation, a covalent bond is broken and a bound electron is transformed into a free electron. Thermal energy is one of the agents which causes pair generation.

⇒ It is likely that the electron in the conduction band may lose its energy due to collision with other particles in the lattice and fall into the valence band. 

⇒ When a free electron falls into a valence band, it merges with a hole. This process is called recombination.