Semiconductor Devices

Q: The dominant mechanisms for motion of charge carriers in forward and reverse biased silicon P-N junctions are –

(A) Drift in forward bias, diffusion in reverse bias

(B) Diffusion in forward bias, drift in reverse bias

(C) Diffusion in both forward and reverse bias

(D) Drift in both forward and reverse bias

Solution : The dominant mechanisms for motion of charge carriers in forward and reverse biased silicon P-N junctions are Diffusion in forward bias, drift in reverse bias .

Correct option is (B)

Q: The approximate ratio of resistances in the forward and reverse bias of the PN-junction diode is –

(A) 10² : 1

(B) 10^–2 : 1

(C) 1 : 10^–4

(D) 1 : 10⁴

Solution : The approximate ratio of resistances in the forward and reverse bias of the PN-junction diode is $\large \frac{R_f}{R_r} = \frac{1}{10000}$

Correct option is (D)

Q: A semiconductor device is connected in a series circuit with a battery and resistance. A current is found to pass through the circuit. If the polarity of the battery is reversed, the current drops almost to zero. The device may be –

(A) A P-type semiconductor

(B) An N-type semiconductor

(C) A P N-junction

(D) An intrinsic semiconductor

Solution : A P-N junction diode conducts when it is reverse biased and does not conduct when it is reversed .

The correct option is (C)

Q: When reverse bias in a junction diode is increased the width of depletion layer –

(A) increase

(B) decreases

(C) does not change

(D) fluctuate

Solution : In reverse biasing width of depletion layer of junction diode increases and resistance of junction diode increases .

Q: Which of the following statements is correct ?

(A) The depletion region of P-N junction diode increases with forward biasing

(B) The depletion region of P-N junction diode decreases with reverse biasing

(C) The depletion region of P-N junction diode does not change with biasing

(D) The depletion region of P-N junction diode decreases with forward biasing

Solution : The depletion region of P-N junction diode decreases with forward biasing & increases with reverse biasing .Hence resistance of junction diode becomes low in forward biasing and becomes high in reverse biasing .

Correct option is (D)

Q: The main cause of Zener breakdown is

(A) the base semiconductor being germanium

(B) production of electron-hole pair due to electric field

(C) low doping

(D) high doping

Solution : The main cause of Zener breakdown is production of electron-hole pair due to electric field .

Correct option is (B)

Q: The main cause of avalanche breakdown is –

(A) collision ionization

(B) high doping

(C) recombination of electron and holes

(D) none of these

Solution : The main cause of avalanche breakdown is collision ionization .

Correct option is (A)

Q: Just before the reverse breakdown in a semiconductor diode :

(A) The forward current is much larger then the reverse current

(B) The forward current is much less then the reverse current

(C) The forward current is equal to the reverse current

(D) The reverse current is much large than the forward current

Solution : Just before reverse breakdown the forward current is much larger than reverse current .

Correct option is (A)

Q: No bias is applied to a P-N junction, then the current –

(A) Is zero because the number of charge carriers flowing on both sides is same .

(B) Is zero because the charge carriers do not move

(C) Is non-zero

(D) None of these

Solution : If no biasing is applied then number of charge carriers flowing on both the sides will be same and hence current will be zero .

Correct option is (A)

Q: If no external voltage is applied across P-N junction ,there would be –

(A) No electric field across the junction

(B) An electric field pointing from N-type to P-type side across the junction

(C) An electric field pointing from P-type to N-type side across the junction

(D) A temporary electric field during formation of P-N junction that would subsequently disappear

Solution : Without an external bias, an electric field exists which points from n to p side and opposes any diffusion of electrons .

Correct option is (B)