Semiconductor Materials
Tunneling
Solved Example: 9962-01
Tunnel diode is a p-n diode with: (ISRO (VSSC) Tech Asst Electronics 2018)
A. Very high doping in p region
B. Very high doping in n region
C. Very high doping in both p and n regions
D. Low doping in both p and n regions
Correct Answer: C
Solved Example: 9962-02
Which of the following options about tunnel diodes is INCORRECT? (PGCIL DT Electrical Aug 2021)
A. The width of depletion region is high compared to the P-N junction.
B. Impurity concentration is high as compared to P-N junction.
C. The V-I characteristics show the negative resistance region.
D. Carrier velocities are very high.
Correct Answer: A
Solved Example: 9962-03
The V-I characteristics of a tunnel diode exhibit: (ESE Electronics 2012)
A. Current-controlled negative resistance
B. Voltage-controlled negative resistance
C. Temperature-controlled positive resistance
D. Current-controlled positive resistance
Correct Answer: B
Solved Example: 9962-04
In the tunnel diode, the Fermi level lies: (ESE Electronics 2018)
A. Inside valence band of p-type and inside conduction band of n-type semiconductors
B. In the energy band gap but closer to the conduction band of n-type semiconductors
C. In the energy band gap but closer to the valence band of = p-type semiconductors
D. In the energy band gap but above valence band of p-type and below conduction band of n-type semiconductors
Correct Answer: A
Diffusion-Drift Current
- Diffusion is the movement of particles in a solid from an area of high concentration to an area of low concentration, resulting in the uniform distribution of the substance.
- Diffusion is cause by Concentration Gradient.
- There are two principle mechanisms by which charge move in a particular direction, thus creating an electric current.
- Drift
- Diffusion
Solved Example: 9928-01
In a semiconductor, Drift current is due to: (DFCCIL Executive Electrical 2016)
A. Volume gradient
B. Diffusion of charge
C. Concentration gradient
D. Applied electric field
Correct Answer: D
Solved Example: 9928-02
Drift current in semiconductors depends upon: (GATE EC 2011)
A. Only the electric field
B. Only the carrier concentration gradient
C. Both the electric field and carrier concentration
D. Both the electric field and carrier concentration gradient
Correct Answer: C
Solved Example: 9928-03
Charge velocity is defined as the: (DFCCIL Executive Electrical Sept 2021)
A. Holes moving at the Fermi speed
B. Electrons moving at the Fermi speed
C. Speed with which the effect of EMF is experienced at all parts of the conductor resulting in the flow of current
D. Speed with which charge drifts in a conductor
Correct Answer: D
Solved Example: 9928-04
If the drift velocity of holes under a field gradient of 200 V/m is 100 m/s, their mobility is SI units is: (ESE Electronics 2012 Paper I)
A. 0.5
B. 0.05
C. 50
D. 500
Correct Answer: A
Energy Bands
Solved Example: 9929-01
In terms of energy bands, semiconductors can be defined as those materials that have: (UPPCL JE Nov 2019 Shift I)
A. Almost an empty conduction band and almost filled valence band with a very narrow energy gap between the conduction and valence band.
B. Almost an empty conduction band and almost filled valence band with a very high energy gap between the conduction and valence band.
C. Almost and empty conduction band and low filled valence band with a very narrow energy gap between the conduction and valence band.
D. Almost full conduction band and almost filled valence band with a very narrow energy gap between the conduction and valence band.
Correct Answer: A
Solved Example: 9929-02
Which of the following is correctly ordered according to the ascending order of band gap energy? (PGCIL Diploma Trainee EE Nov 2018)
A. Silicon, Graphite, Diamond
B. Graphite, Silicon, Diamond
C. Silicon, Diamond, Graphite
D. Diamond, Graphite, Silicon
Correct Answer: B
Solved Example: 9929-03
The energy which any electron possesses at 0 K is: (DFCCIL Executive Electrical 2016)
A. Fermi level
B. Valence energy
C. Exergy
D. Conduction energy
Correct Answer: A
Solved Example: 9929-04
For elements having energy gap more than 5 ev, act as: (DFCCIL Executive Electrical 2016)
A. Semiconductors
B. Insulators
C. Superconductors
D. Conductors
Correct Answer: B
Solved Example: 9929-05
Forbidden energy gap in an atom is the gap between the: (PGCIL Diploma Trainee EE Sep 2018)
A. Second and valence band
B. Valence band and conduction band
C. First and Second band
D. First and valence band
Correct Answer: B
Doping Bands
Solved Example: 121212
A p-type semiconductor is obtained if we dope ________. (SSC Scientific Asst Nov 2017 Shift II)
A. Silicon with a pentavalent element
B. Silicon with a trivalent element
C. A pentavalent element with Silicon
D. A trivalent element with Silicon
Correct Answer: B
Solved Example: 23232
In an n-type doped semiconductor, the Fermi level is: (ISRO VSSC SA Physics Aug 2017)
A. Closer to the conduction band edge
B. Closer to the valence band edge
C. Exactly at the middle of the bandgap
D. Within the conduction band
Correct Answer: A
Solved Example: 3434
In an extrinsic semiconductor doped with trivalent impurity: (SSC Scientific Asst Physics Nov 2017 Shift I)
A. Both electrons and holes become majority carriers
B. Both electrons and holes become minority carriers
C. Electrons become the minority carriers and holes the majority carriers
D. Electrons become the majority carriers and holes the minority carriers
Correct Answer: C
P-N Theory
Solved Example: 1212
A forward biased PN junction diode has a resistance of the order of: (URSC ISRO Tech Asst Electronics Nov 2016)
A. $\Omega$
B. k$\Omega$
C. M$\Omega$
D. None of the above
Correct Answer: A
Solved Example: 23232
For every 10$^\circ$C increase in temperature, the reverse saturation current of a p-n junction will be increased by: (ISRO VSSC Tech Asst Electronics 2018)
A. 10 times
B. 2 times
C. 4 times
D. remains same
Correct Answer: B
Solved Example: 34343
Which of the following is a characteristic of a reverse-biased p-n junction? (PGCIL Diploma Trainee EE Dec 2020)
A. Very narrow depletion region
B. Large current flow
C. Almost no current
D. Very low resistance
Correct Answer: C
Solved Example: 45454
Breakdown of a P-N diode may occur due to: (MPSC AMVI Paper II: Set A/2013)
A. Thermal instability
B. Tunneling effect
C. Avalanche multiplication
D. All the above
Correct Answer: D
Solved Example: 5656
The dynamic resistance of diode varies as: (ISRO Scientist EC 2016)
A. $\dfrac{1}{I^2}$
B. $\dfrac{1}{I}$
C. I
D. $I^2$
Correct Answer: B
Solved Example: 67676
Choose the INCORRECT statement with regard to a forward biased P-N diode. (SSC JE EE Oct 2020 Evening)
A. The junction offer low resistance to current flow
B. The potential barrier is constant irrespective of magnitude of the applied voltage
C. Current flows in the circuit due to the establishment of low resistance path
D. The potential barrier is reduced and at some forward voltage, it is eliminated
Correct Answer: B
Solved Example: 78787
A simple PN junction diode is fabricated using _______ semiconductor and can be used as a _________. (HPCL Engineer Instrumentation Aug 2021)
A. Intrinsic, unidirectional switch
B. Extrinsic, unidirectional switch
C. Extrinsic, bidirectional switch
D. Intrinsic, bidirectional switch
Correct Answer: B