Read the passage and answer the following questions :
The physics of semiconductor devices is dependent on the physics of semiconductors itself. The most important semiconductors are Germanium, Silicon and Gallium Arsenide. The GaAs has different properties than Silicon or Germanium. Pure silicon is intrinsic and contains negligibly small amount of impurities. Each silicon atom shares its four valance electrons with the four neighbouring atoms forming covalent bonds. An extrinsic silicon is achieved by introducing the impurities. The band structure of a solid can be obtained by solving a Schrodinger equation of an approximate one electron problem.
Fermi Level Position in N-type Semiconductor
The Fermi level (EF) represents the energy level at which there is a 50% probability of finding an electron at absolute zero temperature. In semiconductors, its position indicates the type and concentration of charge carriers.
N-type Semiconductor Characteristics
An n-type extrinsic semiconductor is created by doping a pure semiconductor with donor impurities. These impurities introduce extra electrons, making electrons the majority charge carriers. Consequently, the electron concentration ($n$) in the conduction band is significantly higher than the hole concentration ($p$) in the valence band.
Fermi Level Shift
The position of the Fermi level is strongly influenced by the majority carrier concentration. Since electrons are the majority carriers in an n-type semiconductor, their higher concentration pushes the Fermi level upwards from the middle of the bandgap.
- In intrinsic semiconductors, the Fermi level lies near the middle of the bandgap.
- In n-type semiconductors, the increased electron concentration causes the Fermi level to rise closer to the conduction band.
Conclusion
Therefore, for an n-type extrinsic semiconductor, the Fermi level lies below the conduction band, but closer to it than to the valence band. The exact position depends on the doping concentration and temperature.
Important Questions from Semiconductor Materials
Which of the following IS a pentavalent impurity?
A bar of Gallium Arsenide (GaAs) is doped with Silicon such that the Silicon atoms occupy Gallium and Arsenic sites in the GaAs crystal. Which one of the following statements is true?
The outermost orbit of a Germanium atom has ________ electrons.
P-type extrinsic semiconductor doped with impurity having how much valence electron?
All semiconductors in their last orbit have
