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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits1 Mark
Question
In a semiconductor:
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Answer

  1. There are no free electrons at 0K.
  1. The number of free electrons increases with temperature.
  2. The number of free electrons is less than that in a conductor.
Explanation:
In semiconductors, the valence band is full at 0K, but the conduction band is empty. So, no free electron is available for conduction at 0K.
As the temperature increases, covalent bonds that provide free charge carriers for conduction in a semiconductor break.
As the conduction band in metals is already partially filled at 0K, many free electrons below the Fermi level acquire energy from an external source or temperature, jump to the conduction band and start behaving like free electrons. Hence, metals contain more free electrons than semiconductors.

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