Basic Electronics Interview Question Short Question Answer - 2

Explain the term : Forbidden energy gap

Forbidden energy gap
  • The separation gap between valance band and conduction band is known as forbidden energy gap.
  • The forbidden energy gap of the insulator 15eV whereas it is only 1eV for semiconductor.

How covalent bonds are created?

  • The covalent bonds are formed by losing, gaining or sharing electrons with neighboring atoms.

Explain the term : Crystal

  • It is a substance in which atoms or molecules are arranged in proper pattern.

Why the silicon and germanium is most popular semiconductor materials?

  • The energy required to break covalent bonds in the silicon and germanium is very small ( in the silicon 1.1eV and in the germanium 0.7eV ) as compared to other semiconductor material therefore they are the most popular semiconductor material.

What is effect on temperature on the semi-conductor?

Effect of temperature on semi conductor
  • The covalent bonds are very strong in the semiconductor material at absolute zero temperature ( 0 degree Kelvin or -273.15 degree Celsius) resulting no free electrons.
  • Therefore the semiconductor behaves as a perfect insulator.
  • Some of the covalent bonds above absolute zero temperature are breaking result some electrons becomes free for the formation of new covalent bonds. Therefore only few electrons are available for current.

Why the temperature co - efficient of resistance of the semi-conductor is negative?

  • The temperature co - efficient of the semi-conductor is negative because the resistance of the semiconductor decreases with increase in the temperature.

What is hole current?

Hole current
  • The missing electrons in the covalent bonds are called as hole which acts as a positive charge. The flow of current due to positive charge or holes is called as hole current.

Define : Intrinsic semiconductor

Intrinsic semiconductor
  • A pure semiconductor material is known as intrinsic semiconductor.

Define : Extrinsic semiconductor

Extrinsic semiconductor
  • A semiconductor material in which impurities are added is called as extrinsic semiconductor.

Explain the term : P type semiconductor

P – type semiconductor
  • When a small amount of trivalent (Gallium, indium, aluminum, boron etc...) is added to semiconductor material, it is known as P-type semiconductor.

Explain the term : N type semiconductor

N – type semiconductor
  • When a small amount of pentavalent (Arsenic, antimony, phosphorous etc...) is added to semiconductor material, it is known as N-type semiconductor.

Explain the term : Doping

  • The process of adding either pentavalent or trivalent impurities is known as doping.

Explain the term : Depletion layer

Depletion layer
  • The term depletion means empty. When the PN junction is formed a thin layer is set up on both sides of the junction.
  • As there are no free charge carriers in this layer, it is called as depletion layer.

  • The recombination of free and mobile electrons and holes produces narrow layer or region at the junction is called as depletion layer.

Explain the term : Potential barrier

Potential barrier
  • The PN junction diode has large numbers of oppositely charged ions in rows on both sides of depletion layer.
  • Therefore an electrical potential is established across the junction even if the PN junction diode is not connected to the external source of emf. This potential difference is called as potential barrier.

     Potential barrier for Si : 0.7 Volt and Ge :  0.3 Volt

Explain the term : Forward bias

Forward – bias
  • When the external voltage of sufficient magnitude is applied to the PN junction diode in such a direction that it allows the flow of current through the junction, it is called as forward bias.

Explain the term : Reverse bias

Reverse – bias
  • When external voltage is applied to the PN junction diode in such a direction that potential barrier is increased, it is called as reverse biased.

Define : Breakdown voltage

Breakdown voltage
It is minimum reverse voltage at which PN junction breaks down and allows sharp flow of reverse current.

Define : Knee voltage

Knee voltage
  • It is the forward voltage at which current through the PN junction start to increase rapidly. 
  • The knee voltage for the Silicon diode is 0.3V and for the Germanium diode is 0.7 V.

Define : Peak inverse voltage ( PIV )

Peak inverse voltage ( PIV )
  • It is maximum reverse voltage that can be applied to the PN junction diode without damaging it.

Give reason : The P-type and N-type semiconductor material is electrically neutral

Electrically neutral material
  • The conduction of current is the N type semiconductor material is due to excess of electrons whereas in the P type material is due to excess of holes. 
  • We think that ‘The N type material has net negative charge and P type material has net positive charge’ but this statement is absolutely wrong. 
  • The N type material has excess of electrons but these electrons were supplied by donor type impurity and each atom of this donor type impurity is neutral. 
  • The term excess electrons mean that numbers of electrons needed to complete the covalent bonds in the semiconductor material.
  • Therefore we can say that N type semiconductor as well as P type semiconductor is electrically neutral.

Why silicon is mostly preferred as semiconductor device materials as compared to the germanium?

  • The silicon is preferred as semiconductor device material as compared to the germanium due to following reasons
  • The working temperature of the germanium is approx 70 0C whereas it is 150 0C for the silicon. 
  • The variation of the collector leakage current with temperature in the germanium is more than that of silicon. 
  • At room temperature, the collector leakage current in the silicon is much smaller than that of germanium. In the germanium material, the collector leakage current is approx. 10 to 100 times greater than that of silicon type material.

Which are the donor and acceptor type impurity?

Donor Impurity
  • Arsenic, Antimony, Phosphorous

Acceptor Impurity
  • Gallium, indium, Aluminum, Boron

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