Semiconductor Physics

Choose the correct answer

1. In the depletion region of a PN junction diode there is a
shortage of [ ]
a) Acceptor ions b) Holes and electrons c) Donor ions
d) None
2. A PN junction acts as a [ ]
a) Controlled switch c) Bidirectional
switch
b) Unidirectional switch d) None
3. In a PN junction, diode p-side is earthed and n-side is given a
potential -2V. The diode shall
[ ]
a) conduct b) not conduct c) conduct partially d)
break down
4. a PN junction has a thickness of the order of [
]
a) 1 cm b) 1 mm c) 1 μm d) 1 pm
5. in a PN JN diode the motion of majority carriers is due to the
process of [ ]
a) diffusion b) translation c) drift d) rotation
6. in a PN JN diode the motion of minority carriers is due to the
process of [ ]
a) diffusion b) translation c) drift d) rotation
7. in a diode the reverse current is due to drift of free electrons
and holes caused by
[ ]
a) thermal excitation only c) impurity atoms only
b) both a & b d) none
8. in a JN diode the direction of diffusion current is from [
]
a) n-region to p-region c) p-region to n-region
b) p-region to n-region in FB d) None
9. on increasing current in a PN JN diode the potential barrier
will [ ]
a) increases b) decreases c) zero d) does not
changes
10. in a PN JN with no external voltage the electric field
between acceptors and donors is called a
[ ]
a) Peak b) Barrier c) Threshold d) Path
11. PN JN failure below 5V is caused by
[ ]
a) Avalanche break down c) Zener break down
b) break down voltage d) Both a & b
12. the Fermi level in a p-type semiconductor lies close to
[ ]
a) top of the valence band c) bottom of the valence band
b) top of the conduction band d) bottom of the conduction
band
13. if f(ε) is fermi dirac distribution function, then 1- f(ε) is
the probability of [ ]
a) that state is empty < Ef c) That state is filled < Ef
b) that state is empty > Ef d) that state is filled > Ef
14. An intrinsic semiconductor has following properties
[ ]
(i) Its electron concentration = hole concentration
(ii) its carrier density increase with temperature
(iii) its conductivity decreases with temperature
a) (i), (ii) & (iii) b) (ii) & (iii) c) (i) & (iii)
d) (i) & (ii)
15. for P-type SC the dopant is [
]
a) phosphorous b) Antimony c) Bismuth
d) Boron
16. Forbidden energy gap in an atom is the gap between the
[ ]
a) gap between energy levels of valence band
b) gap between energy levels of conduction band
c) gap between valence band and conduction band
d) None of the above
17. The energy which possessed by any electron at 0K is
[ ]
a) valence energy b) Fermi energy c) Conduction energy
d) all the above
18. Drift current is due to [
]
a) applied electric field over a given distance c) Random
motion of electrons
b) Random motion of holes d) Recombination of holes
and electrons
19. Diffusion current is due to [
]
a) applied electric field over a given distance c) Variation in
carrier concentration
b) Random motion of holes d) Recombination of holes
and electrons
20. is the statement diffusion current produces drift current
true [ ]
a) yes b) no c) cannot say d) in
sufficient data
21. In intrinsic semiconductor the carrier concentration
varies as [ ]
3/2
a) 1/T b) T c) T2 d) T
22. At 0 K pure silicon is [
]
a) an intrinsic semiconductor c) extrinsic semiconductor
b) insulator d) a super conductor
23. in an intrinsic semiconductor [
]
a) σ = nμee b) σ = pμhe c) σ = e(nμe+pμh)
d) nμee>pμhe
24. the acceptor levels are expected to be located at ------
above valence band [ ]
a) 0.01 eV b) 0.02 MeV c) 0.01 MeV
d) 0.02 eV
25. Which of the following band are empty at 0K in p-type
semiconductor [ ]
a) valence band b) conduction band c) acceptor levels
d) a & b
26. At temperature > 0 K the number of ionized acceptor
atoms are 10×1014. Then the no of holes are in valence band
[ ]
 a) 5 ×1014 b) 10×1014 c) 20 ×1014 d) 10
7
×10
27. At 0K the fermi energy level EF is =
[ ]
a) Ev-EA/2 b) Ec+Ev/2 c) EA+Ec/2 d)
EV+EA/2
28. Which of the following converts to intrinsic
semiconductor at high temperatures
[ ]
a) Extrinsic b) N-type c) P-type d) b & c
29. In case of semiconductors, recombination is
[ ]
a) Merging of two electrons
b) Merging of two holes
c) Merging of one electron and one hole
d) Merging of outside electron with another semiconductor
electron
30. In semiconductors, the agents which cause electron-hole
pair generation are [ ]
a) Mechanical stress c) Optical illumination
b) Thermal energy d) Both b and c
31. Which one of the following is a correct equation for hall
voltage? [ ]
a)Vh=Rh(1/t * B) b) Vh=Rh(t * B) c) Vh=1/t * B d)
None of the above
32. The hall voltage typical value is around ______volts
[ ]
a)mV b) nano volts c) kilo volts
d) none of the above
33. If metal or semiconductor carrying current is placed in
a magnetic field ┴ to current an electric filed is induced in a
direction ┴ to both current and magnetic field. this
phenomenon is knowns as [ ]
a) chemical effect b) Toxicity c) Halls effect
d) Blister effect
34. Conductivity of n-type semiconductor is ratio of charge
mobility and [ ]
a) current density b) hall coefficient c) current
d) hall voltage
35. The force experienced by a charged particle ‘q’ moving
with velocity ‘v’ through magnetic field ‘B’ and an electric
field ‘E’ is known as [ ]
a) Faraday’s force b) Lorentz force c)Newton’s force
d) Kepler’s force
36. The Hall coefficient is _____ if the number of positive
charges is more than the negative charges.
[ ]
a)Zero b) Negative c) Positive d) Neither b nor
c
37. The density of charge carriers in a pure semiconductor is
proportional to [ ]
−E −2 E −E −E
a) e ( KT ) b) e ( KT ) c) e ( K T ) d) e ( 2 KT )
g g g g
2

38. In N-type semiconductor density of electrons in the

conduction band is given by
[ ]
a) n=2 ¿ c) n=¿
b) n=¿ d) n=¿
39. In an P-type semiconductor the density of holes in
valence band is given by
[ ]
a) p=¿ c) p=¿
b) p=¿ d) p=¿
40. For an N-type semiconductor the Hall coefficient RH is
related to carrier concentration n by
[ ]
a) RH = -ne b) RH = -n/e c) RH = -e/m d) RH
= -1/ne
41. If the Hall coefficient is negative then the semiconductor
is [ ]
a) p-type b) intrinsic c) n-type d) extrinsic
42. Choose the wrong statement
Measuring the hall coefficient one can calculate
[ ]
a) mobility of charge carrier c) Concentration of charge
carrier
 b) type of semiconductor d) energy gap of the
semiconductor
43. The drift velocity of electrons is
[ ]
a) Je/n b) Jn/e c) J/ne d) ne/J
44. The temperature coefficient of semiconductor is
[ ]
a) Zero b) Positive c) Negative d)
None
45. As the temperature increases the resistivity of
semiconductors [ ]
a) increases b) decreases c) unchanged d)
none
46. The sum of probabilities to find an electron and hole is
equal to [ ]
a) one b) zero c) two d) three
47. The energy gap of semiconductor is
[ ]
a) constant c) varies with voltage
b) varies with temperature d) varies with doping
concentration
48. In an intrinsic semiconductor at 0K the Fermi level lies
[ ]
a) at the centre of top of the valence band and bottom of the
conduction band
b) at the centre of donor level and intrinsic fermi level
c) at the centre of donor level and bottom of the conduction
band
d) at the centre of acceptor level and top of the valence band

Fill in the blanks:

1. Majority charge carriers move away from the depletion layer
when the PN JN is ---- biased ( Reverse)
2. PN JN diode is used as a ----------- ( Rectifier)
3. A reverse bias PN JN diode has ---- current ( Zero)
4. In semiconductor Drift current is due to --------- ( applied
electric field)
 ∞

5. The expression ∫ N ( E ) f ( E ) dE gives ---------- ( electron

Ec

concentration in conduction band)

6. The band gap of Si at 300 K is ------(1.12 eV)
7. Majority carriers of P-type material is --------- (holes)
8. The carrier concentration formula in intrinsic semiconductor
is ----------¿)
9. ----- is the average velocity in the direction of the electric field
( Drift velocity)
10. Ease of current drift is ----- (Mobility)
11. The diffusion current in semiconductor is proportional to
--------( concentration gradient of charge carrier)
12. The reason of current flow in PN JN in forward bias is
-------( diffusion of charge carriers)
13. The width of the depletion region in a PN JN diode is
measured in ----- bias ( Reverse)
14. In intrinsic semiconductor the electron concentration is
equal to ----- ( hole concentration)
15. The region in which further increase in temperature
does not produce holes is--------( saturation region)
16. The temperature at which the p-type semiconductor
behave as insulator is ----(0K)
17. At equilibrium the fermi energy level lies ------ of valence
band and acceptor band ( Mid way)
1
f ( ε )=
18. The fermi Dirac distribution function ( E −E
f
)
(1+ e KT )
explains-------- (The probability of energy level to be occupied
by silicon atoms)
19. In a semiconductor after the electron-hole pair
generation the electrons are excited to _________________
(conduction band)
20. When a free electron falls into valance band, it merges
with a hole. This process is called _________________
( Recombination).
21. At higher temperatures the n-type semiconductor
behaves as an _________________ (Intrinsic semiconductor).
22. The level of fermi energy of an N-type semiconductor
when compared to that of intrinsic semiconductor is ----------
(higher)
 23. As the temperature of material increases the top most
completely filled energy level is ----- (Decreases)

Key for MCQ:

1 b 13 a 25 d 37 d
2 b 14 d 26 b 38 b
3 a 15 d 27 d 39 c
4 c 16 c 28 d 40 c
5 a 17 b 29 c 41 d
6 c 18 a 30 d 42 c
7 a 19 c 31 d 43 c
8 b 20 a 32 a 44 b
9 b 21 b 33 c 45 a
10 b 22 b 34 b 46 a
11 c 23 c 35 b 47 a
12 a 24 a 36 c 48 a