My book states,
" At absolute zero temperature, the electrons are tightly bound by the atoms. At this temperature, the covalent bonds between silicon atoms remain very strong and all the valence electrons are engaged in forming covalent bonds. So, no free electrons are available. The valence band of the semiconductor crystal is completely filled, and the energy gap between the valence and conduction band becomes large.
Now, how does the energy gap increase? My intuition is that as the energy bands (energy ranges) become narrower due to the temperature decreasing, the book states the gap between the bands also increases. Am I correct?