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Question
Explain why does conductivity of germanium crystals increase on doping with galium.
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Solution
- When Ge is doped with group 13 elements, for example, gallium, the structure of crystal lattice does not change.
- 3 valence electrons of gallium are used up in the normal covalent bond.
- For one dopant atom, one hole is created because the place where fourth electron is missing is called vacancy or hole and is responsible for conduction of germanium doped with gallium.
Electron from neighbouring atom comes and fills the hole, thereby creating a hole in its original position. Under the influence of electric field electrons move towards positively charged plates through these and conduct electricity. The holes appear to move towards negatively charged plates.
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