P-N-Junction and Diodes

THE P-N JUNCTION

Is the region in which p – type and n – type semiconductors are joined.

THE OPERATION OF P-N JUNCTION

As soon as p-n junction is made electrons cross over the boundary from the n- type material to holes in the p- type, to recombine with the holes. At the same – time holes cross over from p -side to the n – type and capture electrons.

The movements of holes and electrons cause the n- side to become positively charged and p -side to become negatively charged hence creates a Potential difference (Pd) across the barrier. The Potential difference created also creates a barrier and stops the flow of electrons and holes.

DEPLETION LAYER

Is the region near the boundary fairly free of majority charge carriers.

  

JUNCTION VOLTAGE

Is the potential difference across the depletion layer. The junction voltage of silicon is about 0.7 V and 0.3 V for germanium.

FORWARD BIASED OF A P – N JUNCTION

This occurs when the P – type block of p-n junction is connected to the positive terminal of a battery and n-type block is connected to the negative terminal.

The positive charge applied to the p – type repels the holes at the same times the negative charges repels the electrons, hence the width of the depletion layer become reduced and lower potential barrier.

-          With the increase of bias voltage, the non – conducting depletion layer eventually becomes so thin that the charge carriers can pass across the barrier.

-          The electrons which pass the junction barrier inter the p – type region makes the flow of an electric current possible.

REVERSE BIAS OF A P – N – JUNCTION

Occurs when p – type block is connected to the negative terminal of the battery and n – type block of p-n junction is connected to positive terminal of the battery.

The negative charges applied to the p-type attracts the holes at the same time the positive charges applied to the n-type attracts the electrons in the n-type and hence depletion layer become more wide and increases the electrical resistance against the flow of charge carriers. For this reason there will be Minimum or no electrical current flowing due to minority charge carries across the junction.

BREAKDOWN VOLTAGE

Is the voltage at which the p-n junction breaks down.

DIODES

Is an electrical device that allows current flowing through it in one direction only.

OR

Is an electrical device that permits currents to flow in only one direction.

Note: -

The Magnitude of electrical current through the diode depends on the current in the external circuit.

TYPES OF DIODES

The most common types of diodes are.

1.       Semiconductor diode.
2.       Metal semiconductor diode.
3.        Light emitting diodes.
4.       Zener diode.