A semiconductor has a band gap of 1.5 eV. What is the minimum wavelength in nm required to promote an electron from the valence to the conduction band?

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Answer 1 · 2018-05-14T14:08:55

# lambda = 827.5 nm#

To raise an electron from valence to conduction band , the energy required is

equal to the band gap in eV which has a value 1.5 eV as given

If a photon of energy E is absorbed by an electron then for the transfer

E = 1.5 eV = h. #nu# where h is plank's constant and

#nu# is the frequency.

as frequency # nu = c/ lambda # ,therefore

#h.c /lambda #= 1.5 eV or

#lambda = h.c / (1.5 eV) #

substituting the values of h and c and eV in Joules we get

#lambda # = #{ (6.62 . 10^-34) J-s .(3 . 10^8 m/s)} /{(1.5) . 1.60 . 10^-19 J}#

#lambda = 827.5 nm#