PN Junction Diode: Forward Biasing

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18 Questions

What is the result of the transfer of free electrons from the n-type semiconductor into metal near the contact?

Energy band bending

What happens to the potential barrier ΦB across the semiconductor when the Fermi energy of metal becomes lower than the Fermi energy in the semiconductor?

It reduces

What is the direction of the current generated across the MS junction under forward biasing?

From semiconductor to metal

What happens to the depletion region as the applied voltage is continuously increased under forward biasing?

It becomes very thin and finally disappears

What is the direction of the applied bias on the metal in reverse biasing?

Negative

What is the purpose of the LED series resistance in reverse biasing?

To limit the current

What is the primary characteristic of the Schottky barrier?

Surface potential-energy barrier

Where is the built-in-voltage primarily present?

Primarily inside the n-type semiconductor

What is the result of the net loss of electrons at the metal-semiconductor interface?

A depletion region and a growing barrier at the semiconductor surface

What is the energy required for electrons to flow from the n-type semiconductor to the metal?

Greater than the built-in-voltage

What is the width of the region where electrons move into the metal compared to the width inside the n-type semiconductor?

Negligibly thin

What occurs when the Schottky diode is unbiased?

Only a small number of electrons flow from the n-type semiconductor to the metal

What happens to a ferromagnetic substance when it is inserted in a current-carrying coil?

It becomes magnetized

What is the term for the process of demagnetizing a substance by reversing the direction of the current?

Hysteresis

What happens to the magnetic flux density (B) when the magnetic field strength (H) is increased from zero to one?

B increases

What is the point where the value of magnetism remains constant even when the magnetic field is increased?

Saturation point

What is the term for the amount of force required to remove a material's retentivity?

Coercive force

What is the result of hysteresis in electric machines' ferromagnetic cores?

Energy loss

Study Notes

Schottky Barrier

  • The net loss of electrons creates a negative charge in the metal and a positive charge in the semiconductor, resulting in a depletion region and a growing barrier at the semiconductor surface.
  • The equilibrium band structure for a metal and a n-type semiconductor is characterized by the Schottky barrier height, ΦB, which is a function of the metal and the semiconductor: ΦB = ΦM - χ.
  • The built-in-potential or built-in-voltage is primarily present inside the n-type semiconductor, preventing further electron flow from the semiconductor conduction band into the metal.

Forward Biasing

  • Under a forward biasing (VA > 0), the Fermi energy of metal becomes lower than the Fermi energy in the semiconductor, EF, reducing the potential barrier ΦB across the semiconductor.
  • This makes it easier for electrons to pass over the barrier, allowing them to diffuse from semiconductor to metal, resulting in a positive current.
  • As the applied voltage increases, the depletion region becomes thinner and finally disappears.

Reverse Biasing

  • With a negative applied bias on the metal (VA < 0), the potential barrier ΦB increases, making it more difficult for electrons to overcome the surface barrier.
  • The depletion region becomes wider, and the current decreases.

Hysteresis Loop

  • The hysteresis loop is formed by continuously monitoring the magnetic flux released by the ferromagnetic substance as the external magnetizing field is altered.
  • The loop is characterized by the saturation point, retentivity point, and coercive force.
  • The hysteresis loop is a cycle of magnetization and demagnetization, with the material retaining some magnetic retentivity, even when the magnetic field is zero.
  • Hysteresis can cause energy loss in electric machines' ferromagnetic cores.

This quiz covers the concept of forward biasing in Metal-Semiconductor (MS) junctions, including the energy band bending and reduction of potential barrier. It's a fundamental topic in electronics and semiconductor physics. Test your understanding of the PN junction diode operation under forward biasing.

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