JEE Main & Advanced Physics Semiconducting Devices Electron Emission from Metal

(1) Free electron in metal experiences a barrier on surface due to attractive Coulombian force.

(2) When kinetic energy of electron becomes greater than barrier potential energy (or binding energy\[{{E}_{b}}\]) then electron can come out of the surface of metal.

(3) Fermi energy \[({{E}_{f}})\]: Is the maximum possible energy possessed by free electron in metal at 0K temperature

(i) In this energy level, probability of finding electron is 50%.

(ii) This is a reference level and it is different for different metals.

(4) Threshold energy (or work function \[{{W}_{0}}\]) : Is the minimum energy required to take out an electron from the surface of metal. Also \[{{W}_{0}}={{E}_{b}}{{E}_{f}}\]

Work function for different materials \[{{({{W}_{0}})}_{\text{Pure tungsten}}}\text{ }\!\!~\!\!\text{ }~=\text{ }4.5eV\]

\[{{({{W}_{0}})}_{\text{Throated tungsten}}}~=\text{ }2.6eV\] \[{{({{W}_{0}})}_{\text{Oxide coated tungsten}}}=\text{ }1eV\]

(5) Four processes of electron emission from a metal are

(i) Thermionic emission        

(ii) Photoelectric emission 

(iii) Field emission 

(iv) Secondary emission