Silicon has a band gap of $1.12 eV$ . Using $h c = 1240 eV nm$ , calculate the longest wavelength of light, in nm, that can excite an electron from the valence band to the conduction band (nearest integer).

Numerical answer type, answer in nm, tolerance 1.

Answer: 1107 nm

A photon must supply at least the band-gap energy,

E = h c / λ \geq E_{g}

. Thus

λ_{ma x} = \frac{h c}{E _{g}} = \frac{1240}{1.12} = 1107.1 nm

, about 1107 nm.