Doping
- The conductivity of metal is increased by adding an appropriate amount of suitable impurity.
- This process is known as doping.
- It can be performed with an impurity which is electron rich or electron deficient than the intrinsic semiconductor silicon or germanium.
Fig. Doping electron rich impurity into an intrinsic conductor
- Such impurities introduce electronic defects in them.
- If NaCl is doped with 10-3mol % of SrCl2, what is the concentration of cation vacancies?
- 1 Cation of Sr2+ = 1 cation vacancy in NaCl.
Number of cation vacancies in lattice of NaCl = Number of divalent Sr2+ ions added.
Concentration of cation vacancy on doping with 10-3 mol% of SrCl2. = 10-3 mol% = 10-3 / 100 = 10-5 mol.
Number of Sr2+ ion in 10-5 mol = 10-5 x 6.023 x 1023 = 6.023 x 1018
Hence number of cationic vacancies = 6.023 x 1018
