The energy gaps between the valence and conduction bands are called band gaps. for silicon, the band gap is 1.1 ev; for fused silica glass, it is 9.3 ev.
what is the wavelength λ of a photon that has energy 1.1ev?
the cut off between visible and infrared light is usually said to be somewhere between 700 and 800nm. why is silicon transparent to most infrared light but opaque to visible light?
a) visible photons have greater energy than the gap, so they can be absorbed whereas infrared photons pass through.
b) visible photons have greater energy than the gap, so they can’t interact with the silicon as the infrared photons can.
c) infrared photons have less energy than the gap, and so, unlike visible photons, they can be absorbed and reemitted from the material.
d) infrared photons have less energy than the gap, and so they are only partially absorbed whereas visible photons are fully absorbed.