Energy required for creation of photoelectron

[paweld]

I found in one book that the energy required for creation of one photoelectron in silicon
is 1.14eV (that's the energy gap between vallence and conduction band). So only photons
with energy higher than 1.14eV can create one free electron. It's understandable for me.

But when the energy is higher (above 3.65 eV - energy required to create electron-hole pair)
two electrns are created. One can explain this in the following way: photons contributes to creation of only one electron (and of course because of it ceases to exist) but this electon
has enough energy to induce another electron.

But why a photon needs only 1.14eV to create and electron when electron needs as much as 3.65 (In order to move an electron from vallence band to conduction band one always needs the same amount of energy?). What the difference between these phenomena?

 

[agtee]

well, for the distinction between creation of a photoelectron and a electron-hole pair is that when photon is imparted on an electron and its removing electron out of silicon, it was an electron which was in conduction band earlier... while for the creation of ele-hole pair is done by moving electron from valance band to conduction band.