Semiconductor Physics PDF

Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions Unit IV Solid State Physics 1 At absolute zero, Si acts as?...

Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions Unit IV Solid State Physics 1 At absolute zero, Si acts as? d) Diamond < silicon < germanium a) non-metal b) metal 9 Energy band formation is prominent in ……. c) insulator d) none of these a) Solids b) Liquids 2 Carbon, Silicon and Germanium atoms have four c) Gases valence electrons each. Their valence and d) All the above conduction bands are separated by energy band gaps represented by (Eg)C, (Eg)Si and (Eg)Ge 10 Elements in gaseous state give rise to ………. respectively. Which one of the following spectrum. relationship is true in their case? a) band a) (Eg)C> (Eg)Si b) (Eg)C 4 13 ………… band contains free electrons. 6 Energy band gap size for insulators is in the a) Valence range ________ eV. b) Conduction a) 1-2 b) 2-3 c) Forbidden c) 3-4 d) 3-6 d) Both valence and conduction 7 Not an example for intrinsic semiconductor 14 ………… band contains valence electrons. a) Si b) Al a) Valence c) Ge d) Sn b) Conduction c) Forbidden 8 Which is the correct ordering of the band gaps d) Both valence and conduction within the group 14 elements? e) a) Diamond > silicon < germanium 15 ………… band does not contain electrons. b) Diamond > silicon > germanium a) Valence c) Diamond < silicon > germanium b) Conduction Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 1  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions c) Forbidden c) good conductor d) Both valence and conduction d) any of the above 16 Electrons exist in ………. 23 An energy band is …………. a) Valence band a) a set of continuous energies b) Conduction band b) a set of closely spaced allowed energy levels c) Forbidden band c) a set of widely spaced allowed energy levels d) Both valence and conduction band d) none of the above e) 17 If N atoms are brought close together to form a 24 What is the origin of energy bands in solids? solid, the s energy band can accommodate a) Atomic mass ………… electrons. b) Temperature a) N b) 2 N c) 6 N d) 8 N c) Closely packed periodic structure of solid d) Atomic number of atoms in solid 18 If N atoms are brought close together to form a solid, the p energy band can accommodate 25 Which of the following decides electrical ………… electrons. properties of a solid? a) N b) 2 N c) 6 N d) 8 N a) Electronic configuration b) Interatomic distance 19 If the outermost energy band in a solid is c) Both Electronic configuration and partially filled, the solid will be ………….. Interatomic distance a) insulator d) Neither Electronic configuration nor b) semiconductor Interatomic distance c) good conductor e) d) any of the above 26 Valence band in a metal contains ……….. a) free electrons 20 If the outermost energy band in a solid is b) holes completely filled, the solid will be ……….. c) valence electrons a) insulator d) both holes and valence electrons b) semiconductor c) good conductor 27 Valence band in a semiconductor contains d) either insulator or semiconductor ……………..Free electrons a) Holes 21 If the outermost energy band in a solid is b) Valence electrons completely filled and the energy difference with c) Both holes and valence electrons the next energy band is small, the solid will be …………….. a) insulator 28 Conduction band in a metal contains…….. b) semiconductor a) free electrons c) good conductor b) holes d) any of the above c) valence electrons d) both holes and valence electrons 22 If the outermost energy band in a solid is completely filled and the energy difference with 29 Conduction band in a semiconductor contains the next energy band is large, the solid will be …………….. …………….. a) Free electrons a) insulator b) Holes b) semiconductor c) Valence electrons Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 2  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions d) Both holes and valence electrons 39 There is no forbidden band in ……… 30 The energy gap in good conductors is …… a) good conductor a) 0 b) ~ 1 eV c) ~ 5 eV b) semiconductor d) none of th above c) insulators d) both semiconductors and insulators 31 The energy gap in insulators is …………… e) a) 0 b) ~ 1 eV c) ~ 5 eV d) 40 The band gap energy in Silicon is……….. none of th above a) 0 b) 0.7 eV 32 The energy gap in semiconductors is …… c) 1.1 eV a) 0 b) ~ 1 eV d) 5 Ev c) ~ 5 eV d) none of the above 41 The band gap energy in Germanium is….. 33 Which of the following has maximum band gap a) 0 energy ? b) 0.7 eV a) Tin b) Silicon c) 1.1 eV c) Germanium d) Carbon in diamond form d) 5 eV 34 Which of the following has minimum band gap 42 Which of the following is not a semiconductor? energy ? a) Silicon a) Tin b) Silicon c) Germanium b) Germanium b) Carbon in diamond form c) GaAs c) d) Carbon 35 Pure semiconductors are known as ………….. a) intrinsic 43 Valence band of a semiconductor at 0 K will be b) doped ……………… c) extrinsic a) completely filled d) compound b) partially filled c) completely empty 36 Impure semiconductors are known as ………….. d) either completely filled or completely empty a) intrinsic b) doped 44 Valence band of a semiconductor at c) extrinsic temperatures above 0 K will be ……… d) compound a) completely filled b) partially filled 37 The donor impurity levels lie ………. c) completely empty a) just above the valence band d) either completely filled or completely empty b) just below the conduction band c) at the centre of forbidden band 45 Conduction band of a semiconductor at 0 K will d) just above the conduction band be ……………… a) completely filled 38 The acceptor impurity levels lie ………. b) partially filled a) just above the valence band c) completely empty b) just below the conduction band d) either completely filled or completely empty c) at the centre of forbidden band d) just above the conduction band 46 Conduction band of a semiconductor at Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 3  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions temperatures above 0 K will be ………… b) Maxwell-Boltzmann a) completely filled c) Fermi-Dirac b) partially filled d) Bose-Einstein c) completely empty d) either completely filled or completely empty 53 Identical particles for which the spin is an odd integer multiple of half which can not be 47 The classical free electron theory of metals was distinguished from one another obey …………….. initiated by ………………… distribution for energy. a) Pauli b) Summerfield c) Lorentz a) Binomial and Drude d) Fermi-Dirac b) Maxwell-Boltzmann c) Fermi-Dirac 48 According to classical free electron theory the d) Bose-Einstein electrons follow ……… distribution of energy. a) Binomial 54 According to classical free electron theory the b) Maxwell-Boltzmann electrons …………… in absence of external electric c) Fermi-Dirac field. d) Bose-Einstein a) remain at rest b) move randomly 49 According to quantum free electron theory the c) have drift velocity electrons follow ……… distribution of energy. d) none of the above a) binomial b) Maxwell-Boltzmann c) Fermi-Dirac 55 ( ) Average kinetic energy E0 of a free electron d) Bose-Einstein gas at 0 K is 2 5 3 a) EF b) EF c) EF 50 According to classical free electron theory the 5 3 5 electrons …………… in absence of external electric d) EF field. a) remain at rest 56 Which of the following, when added as an b) move randomly impurity, into the Silicon, produces n-type semi c) have drift velocity conductor d) none of the above a) Phosphorous b) Aluminum c) Magnesium d) both ‘b’ and ‘c’ 51 Identical particles which are so far apart that they can be distinguished and their wave 57 When arsenic is added as an impurity to Silicon, functions do not overlap obey …………….. the resulting material is distribution for energy. a) n-type semiconductor a) Binomial b) p-type semiconductor b) Maxwell-Boltzmann c) n-type conductor c) Fermi-Dirac e) Insulator d) Bose-Einstein f) 58 To obtain a p-type germanium semiconductor, it 52 Identical particles with zero or integer spins with must be doped with? overlapping wavefunctions which can not be a) Arsenic b) Antimony distinguished obey …………….. distribution for energy. c) Indium d) Phosphorus a) Binomial 59 Which of the following when added acts as an Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 4  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions impurity into silicon produced n-type c) Produced when phosphorous is added as an semi conductor? impurity to silicon a) P b) Al c) B d) Mg d) None of the above 60 A semiconductor is doped with donor impurity is a) p type b) n type 68 A long specimen of p-type semiconductor c)npn type d)pnp type material: a) Is positively charged 61 One serious drawback of semiconductors is b) Is electrically neutral a) they are costly c) Has an electric field directed along its length b) they pollute the environment d) None of the above c) they do not last for long time d) they can’t withstand high voltage 69 When N-type semiconductor is heated, a) number of free electrons increases while that 62 in a p type semiconductor, the acceptor valence of holes decreases band is b) number of holes increases while that of a) above the conduction band of the host crystal electrons decreases b) below the conduction band of the crystal c) number of electrons and holes remain same c) above the valence band of the crystal d) number of electron and holes increases d) below the conduction band of the crystal equally 63 In intrinsic semiconductors, number of free 70 A piece of copper and other of germanium are electrons is __________ number of holes. cooled from the room temperature to 80K, then a) Equal to b) Greater than c) Less than a) resistance of each will increase d) Can not define b) resistance of copper will decrease c) the resistance of copper will increase while 64 In n-type semiconductors, number of holes is that of germanium will decrease __________ number of free electrons. d) the resistance of copper will decrease while a) Equal to b) Greater than c) Less than that of germanium will increase d) Can not define 71 At low temperature, the resistivity of a metal is 65 In p-type semiconductors, number of holes is proportional to ……………… __________ number of free electrons. a) T 2 b) T c) T 5 d) T 12 a) Equal to b) Greater than c) Less than d) Twice 72 The intrinsic semiconductor becomes an insulator at 66 n-type semiconductors are: a) 0°C b) 0K c) 300K a) Negatively charged d) —100°C b) Produced when Indium is added as an impurity to Germanium 73 In semiconductors at a room temperature c) Produced when phosphorous is added as an a) the conduction band is completely empty impurity to silicon b) the valence band is partially empty and the d) None of the above conduction band is partially filled c) the valence band is completely filled and the 67 p-type semiconductors are: conduction band is partially filled a) Negatively charged d) the valence band is completely filled b) Produced when Indium is added as an impurity to Germanium 74 Choose the only false statement from the Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 5  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions following. c) 10-10(Ω-m)-1 a) in conductors the valence and conduction d) 10-8(Ω-m)-1 bands may overlap. b) Substances with energy gap of the order of 5 81 Unit for electric field strength is eV are insulators. a) A/cm2 b) mho/meter c) The resistivity of a semiconductor increases c) cm2/V.s d) V/cm with increase in temperature. d) The conductivity of a semiconductor increases 82 Flow of electrons is affected by the following with increase in temperature. a) Thermal vibrations b) Impurity atoms c) Crystal defects d) all 75 What is the conductivity of semiconductor if free electron density = 5x1012/cm3 and hole density = 83 Mobility of holes is ___________ mobility of 8x1013/cm3? [μe = 2.3 and μh = 0.01 in SI units] electrons in intrinsic semiconductors. a) 5.634 b) 1.968 c) 3.421 d) 8.964 a) Equal to b) Greater than c) Less than d) Can not define The76 Difference in the variation of resistance with 84 The conductivity of an intrinsic semiconductor is temperature in a metal arises essentially due to given by (symbols have the usual meanings): the difference in a) σi = eni2 (µn – µp) a. type of bonding b) σi = eni (µn – µp) b. crystal structure c) σi = eni (µn + µp) c. scattering mechanism with temperature d) None of the above d. number of charge carriers with temperature 85 In an intrinsic semiconductor, the mobility of 77 The difference in the variation of resistance with electrons in the conduction band is: temperature in semiconductor arises essentially a) Less than the mobility of holes in the valence due to the difference in band a) type of bonding b) Zero b) crystal structure c) Greater than the mobility of holes in the c) scattering mechanism with temperature valence band d)number of charge carriers with temperature d) None of the above 78 Resistance of a semiconductor 86 If the drift velocity of holes under a field gradient a) increases with temperature of 100 V/m is 5m/s, the mobility (in the same SI b) decreases with temperature units)is ……… c) remains unaffected with temperature a) 0.05 d) none of these b) 0.55 c) 500 79 The temperature coefficient of the resistance of d) None of the above semiconductors is always a) positive b) negative 87 The electron and hole concentrations in a c) zero d) infinite intrinsic semiconductor are ni and pi respectively. When doped with a p-type 80 Electrical conductivity of insulators is of the material, these change to n and p, respectively. order of _____________. Then: a) 10-10(Ω-mm)-1 a) n + p = ni + pi b) 10-10(Ω-cm)-1 b) n + ni = p + pi Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 6  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions c) np = nipi d) Both semiconductors and insulators d) None of the above 94 Resistivity increases with increase in 88 If the temperature of an extrinsic semiconductor temperature for ………………… is increased so that the intrinsic carrier a) Good conductors concentration is doubled, then: b) Semiconductors a) The minority carrier density doubles c) Insulators b) The majority carrier density doubles d) Both semiconductors and insulators c) Both majority and minority carrier densities double 95 Resistivity decreases with increase in d) None of the above temperature for ………………… a) Good conductors 89 At room temperature, the current in an intrinsic b) Semiconductors semiconductor is due to c) Insulators a) Holes d) Both semiconductors and insulators b) Electrons c) Holes and electrons 96 If a semiconductor is transparent to light of d) None of the above wavelength greater than λ, the band gap energy will be…………. 90 The mobility is given by (notations have their hl hc h lc usual meaning): a) b) c) d) c l l h a) µ = v0/E0 b) µ = v0/E02 97 If the band gap energy of a semiconductor is Eg c) µ = v02/E0 ,the material will be ……… d) None of the above hc a) transparent to wavelength greater than 91 In a p-type semiconductor, the conductivity due Eg to holes (σp) is equal to (e is the charge of hole, hc µp is the hole mobility, p0 is the hole b) opaque to wavelength greater than Eg concentration): a) p0.e/µp hc c) transparent to wavelength less than b) µp/p0.e Eg c) p0.e.µp d) none of the above d) None of the above 98 Which of the following have a positive 92 Near room temperature, resistivity is maximum temperature coefficient of resistance? for………………… a) Good conductor a) Good conductors b) Semiconductor b) Semiconductors c) Insulators c) Insulators d) Both semiconductors and insulators d) Both semiconductors and insulators 99 Which of the following have a negative 93 Near room temperature, resistivity is minimum temperature coefficient of resistance? for………………… a) Good conductor a) Good conductors b) Semiconductor b) Semiconductors c) Insulators c) Insulators d) Both semiconductors and insulators Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 7  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions c) both free electrons and holes 100 Conduction in intrinsic semiconductors is due to d) neither free electrons nor holes ……….. a) only free electrons 107 The charge carriers in p - type semiconductors b) only holes are ………….. c) both free electrons and holes a) free electrons d) positive and negative ions b) holes c) both free electrons and holes 101 If a free electron moves towards right and d) neither free electrons nor holes combines with a hole, the hole ……… a) moves towards right 108 The charge carriers in n - type semiconductors b) moves towards left are ………….. c) remains at the same place a) free electrons d) is neutralized b) holes c) both free electrons and holes 102 If a bound electron moves towards right and d) neither free electrons nor holes combines with a hole, the hole ……… a) moves towards right 109 The majority charge carriers in p - type b) moves towards left semiconductors are ………….. c) remains at the same place a) free electrons d) is neutralized b) holes c) both free electrons and holes 103 In an electric field, an electron initially at rest will d) neither free electrons nor holes move ……… a) in the direction of electric field 110 The majority charge carriers in n - type b) opposite to the direction of electric field semiconductors are ………….. c) perpendicular to the direction of electric a) free electrons field b) holes d) none of the above c) both free electrons and holes 104 In an electric field, a hole initially at rest will d) neither free electrons nor holes move ……… a) in the direction of electric field 111 The resistance of a conductor of unit length and b) opposite to the direction of electric field unit cross section area is known as …………. c) perpendicular to the direction of electric a) resistivity field b) conductivity d) none of the above c) resistance d) conductance 105 Mobility of holes is ………. that of free electrons. a) more than 112 The reciprocal of resistivity is …………. b) less than a) resistivity c) equal to b) conductivity d) can be more or less than c) resistance d) conductance 106 The charge carriers in intrinsic semiconductors are ………….. 113 The reciprocal of resistance is …………. a) free electrons a) resistivity b) holes b) conductivity Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 8  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions c) resistance current due to holes in a semiconductor under d) conductance the influence of an external electric field, the total current is ………….. 114 The amount of charge flowing through unit cross I I section area per unit time is known as ………… a) I e + I h b) I e - I h c) e d) h Ih Ie a) current b) current density 121 The equation for current density is J = c) conductance d) resistance a) nevd b) neavd c) nea d) none of the above 115 The amount of charge flowing through any cross section area per unit time is known as ………… 122 The equation for current is I = a) current b)current density a) nevd b) neavd c) nea d) none c) conductance d) resistance of the above 116 Current in a semiconductor can be due to 123 If an electric field of 10 V / m is applied to n-type a) electric field Germanium in which the mobility of free b) density gradient of charge carriers electrons is 3800 cm2 / V-s, the drift velocity of c) both electric field and density gradient electrons will be ………….. m/s. of charge carriers a) 38000 b) 38 c) 3.8 d) 0.38 d) either electric field or density gradient of charge carriers 124 If an electric field of 10 V / m applied to p-type Germanium gives rise to a drift velocity of 1.7 m 117 The unit for resistivity is ……………. / s for the holes, the mobility of holes is ………….. a) ohm cm2 / V-s. b) ohm / m a) 1.7 b) 17 c) 170 c) ohm-m d) 1700 d) mho / m 125 A small concentration of minority carriers is 118 The unit for conductivity is ……………. injected into a homogeneous semiconductor a) ohm crystal at one point. An electric field of 10 V/cm b) ohm / m is applied across the crystal and this moves the c) ohm-m minority carrier a distance of 1 cm in 20 µsec. d) mho / m The mobility (in cm2/volt.sec) is: a) 10000 b) 20000 c) 50 d) 100 119 Which of the following equations for mobility is correct? 126 If the electrical resistivity of Ti is 4.3 × 10–7 Ω m, vd what is the resistance of a 0.85 m long piece of a) m= E wire of cross section 2.0 × 10–6 m2? s a) 0.18 Ω b) 5.47 Ω c) 0.25 Ω d) 3.95 Ω b) m = ne 1 127 The effective mass of an electron is negative c) m = ……………. ner a) near the bottom of conduction band d) All the above b) near the top of valence band c) in the valence band 120 If Ie is the current due to electrons and Ih is the d) in the forbidden band Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 9  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions a) E > EF b) E < EF c) E = E F 128 The effective mass is same as its mass for d) E >> EF a) near the bottom of conduction band b) near the top of valence band 136 Fermi energy level for intrinsic semiconductors c) in the valence band lies d) in the forbidden band a) At middle of the band gap b) Close to conduction band 129 The effective mass of an electron is positive c) Close to valence band ……………. d) None a) near the bottom of conduction band b) near the top of valence band 137 Fermi energy level for p-type extrinsic c) in the valence band semiconductors lies d) in the forbidden band a) At middle of the band gap b) Close to conduction band 130 The Fermi-Dirac probability distribution function c) Close to valence band is ……………… d) None 1 a) P (E) = ( E- E F ) /kT 1+ e 138 Fermi energy level for n-type extrinsic 1 semiconductors lies b) P (E) = ( EF - E ) /kT a) At middle of the band gap 1+ e b) Close to conduction band 1 c) P ( E ) = ( E- EF ) /kT c) Close to valence band e d) None 1 d) P ( E ) = 1- e ( E- EF ) /kT 139 Fermi level for extrinsic semiconductor depends on 131 The value of Fermi Function at 0K for E < EF is a) Donor element …………. b) Impurity concentration a) 0 b) 1 c) 0.5 d) 0.75 c) Temperature d) All 132 The value of Fermi Function at 0K for E > EF is …………. 140 The density states of electrons between the a) 0 b) 1 c) 0.5 d) 0.75 energy range E and E + dE is proportional to a) E b) E c) E d) E 12 2 32 133 The value of Fermi Function at T > 0K for E = EF is …………. 141 When we increase the temperature of extrinsic a) 0 b) 1 c) 0.5 d) 0.75 semiconductor, after a certain temperature it behaves like …… 134 The probability that an electron in a metal a) an insulator occupies the Fermi-level, at any temperature (>0 b) an intrinsic semiconductor K) is: c) a conductor a) 0 b) 1 c) 0.5 d) a superconductor d) none of the above 142 In a n-type semiconductor, the Fermi level at 0K 135 The value of Fermi-distribution function at is …………… absolute zero ( T = 0K ) is 1, i.e. F(E) = 1, under a) between valence band and acceptor levels the condition ……………. b) between acceptor levels and intrinsic Fermi Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 10  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions level d) none of the above c) between intrinsic Fermi level and donor level d) between donor level and conduction band 149 The Fermi level shifts …………. in n-type semiconductor with increase in impurity 143 In a p-type semiconductor, the Fermi level at 0K concentration. is …………… a) upwards a) between valence band and acceptor levels b) downwards b) between acceptor levels and intrinsic Fermi c) neither upward nor downward level d) none of the above c) between intrinsic Fermi level and donor level d) between donor level and conduction band 150 The Fermi level shifts …………. in p-type semiconductor with increase in impurity 144 In a n-type semiconductor, the Fermi level at T > concentration. 0K is …………… a) Upwards b) downwards a) between valence band and acceptor levels c) neither upward nor downward b) between acceptor levels and intrinsic Fermi d) none of the above level c) between intrinsic Fermi level and donor level 151 A p-n junction is said to be forward biased, d) between donor level and conduction band when a) the positive pole of the battery is joined to the 145 In a p-type semiconductor, the Fermi level at T > p-semiconductor and negative pole to the n- 0K is …………… semiconductor a) between valence band and acceptor levels b) the positive pole of the battery is joined to b) between acceptor levels and intrinsic Fermi the n-semiconductor and negative pole of the level battery is joined to the p-semiconductor c) between intrinsic Fermi level and donor level c) the positive pole of the battery is connected d) between donor level and conduction band to n- semiconductor and p- semiconductor d) a mechanical force is applied in the forward 146 The Fermi level shifts …………. in p-type direction semiconductor with increase in temperature. a) upwards 152 The depletion layer in the P-N junction region b) downwards is caused by? c) neither upward nor downward a) drift of holes d) none of the above b) diffusion of charge carriers c) migration of impurity ions 147 The Fermi level shifts …………. in n-type d) drift of electrons semiconductor with increase in temperature. a) upwards 153 A semi-conducting device is connected in a b) downwards series circuit with a battery and a resistance. A c) neither upward nor downward current is found to pass through the circuit. If d) none of the above the polarity of the battery is reversed, the current drops to almost zero. The device may be 148 The Fermi level shifts …………. in intrinsic a) A p-n junction semiconductor with increase in temperature. b) An intrinsic semi-conductor a) upwards c) A p-type semi-conductor b) downwards d) An n-type semi-conductor c) neither upward nor downward Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 11  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions 154 The cause of the potential barrier in a p-n diode b) lowers the potential barrier is ? c) raises the potential barrier a) Depletion of positive charges near the d) increases the majority carrier current junction b) Concentration of positive charges near the 162 Application of a forward bias to a p—n junction junction a) widens the depletion zone. c) Depletion of negative charges near the b) increases the potential difference across the junction depletion zone. d) Concentration of positive and negative c) increases the number of donors on the n charges near the junction side. d) increases the electric field in the depletion 155 In forward bias, the width of potential barrier in zone. a p-n junction diode? a) increases b) decreases 163 On increasing the reverse bias to a large value in c) remains constant pn junction diode the current: d) first increases then decreases a) Increases slowly b) remains fixed 156 A depletion layer consists of? c) Suddenly increases a)electrons b) protons d) decreases slowly c)mobile ions d) immobile ions 164 The number of …………….. charge carriers 157 The part of depletion layer in the p-type contains increases with increase in temperature in n-type ……….. semiconductor. a) holes b) positive ions a) minority c) free electrons d) negative ions b) majority c) both minority and majority 158 The part of depletion layer in the n-type contains d) neither minority nor majority ……….. a) holes b) positive ions 165 The number of …………….. charge carriers c) free electrons d) negative ions increases with increase in temperature in p-type semiconductor. 159 In a junction diode, the holes are due to a) minority a) protons b) extra electrons b) majority c) neutrons d) missing electrons c) both minority and majority d) neither minority nor majority 160 In an unbiased p-n junction a) The potential of the p and n sides becomes 166 The electrical resistance of depletion layer is higher alternately large because: b) The p side is at higher electrical potential a) it has no charge carriers than the n side b) it has large number of charge carriers c) The n side is at higher electrical potential c) it contains electrons as charge carriers than the p side d) it has holes as charge carriers d) Both the p and n sides are at the same potential 167 In forward biased p-n junction the current is of the order of 161 Reverse bias applied to a junction diode a) ampere b)milliampere a) increases the minority carrier current c) microampere d)nanoampere Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 12  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions a) more in n-type 168 When p-n junction diode is reverse biased the b) more in p-type flow of current across the junction is mainly due c) same in both to d) none of the above a) diffusion of charges b) depends on nature of material 175 The potential difference across an open circuited c) drift of charges p-n junction is known as …………….. d) both drift and diffusion of charges a) knee voltage b) cut-in-voltage 169 The number of …………….. charge carriers c) potential barrier increases with increase in light incident on n- d) none of the above type semiconductor. a) minority 176 The dominant mechanism for motion of charge b) majority carriers in forward and reverse biased silicon p-n c) both minority and majority junction are d) neither minority nor majority a) drift in both forward and reverse bias b) diffusion in both forward and reverse 170 The number of …………….. charge carriers c) diffusion in forward and drift in reverse increases with increase in in light incident on p- d) drift in forward and diffusion in reverse type semiconductor. a) minority 177 If VB is the barrier potential, the energy b) majority difference between the conduction bands of n- c) both minority and majority type and p-type in open circuited p-n junction d) neither minority nor majority diode is ……………… V 171 Application of forward bias to the p-n junction a) eVB b) B c) e + VB e a) increases the number of donors on n side d) e - VB b) increases electric field in depletion region c) increases potential difference across the depletion region 178 If VB is the barrier potential and V is the d) widens the depletion zone applied voltage, the energy difference between e) the conduction bands of n-type and p-type in 172 Within depletion region of the p-n junction forward biased p-n junction diode is ……………… diode a) eVB b) eVB + eV a) p side is positive and n side is negative c) eVB - eV d) V - VB b) p side is negative and n side is positive c) both sides are either positive or negative 179 If VB is the barrier potential and V is the d) both sides are neutral applied voltage, the energy difference between the conduction bands of n-type and p-type in 173 Barrier potential of p-n junction does not reverse biased p-n junction diode is ……………… depend on a) eVB b) eVB + eV a) temperature b) forward bias c) eVB - eV d) V - VB c) reverse bias d) diode design 174 For the same electric field and density of doping 180 Under equilibrium conditions in a p-n junction, in two identical semiconductors, one p-type and the Fermi level in n-type is at ………… level the other n-type, the current will be …………….. than/as that in p-type. a) higher Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 13  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions b) lower c) electrons in p-type and holes in n-type c) same d) holes in p-type and electrons in n-type d) none of the above 187 the recombination of electron hole pairs in a 181 When forward bias is applied to a p-n junction forward biased GaAs diode gives rise to diode, the Fermi level in n-type ………….. with …………….. radiation. respect to the Fermi level in p-type. a) visible a) rises b) infra red b) falls c) ultra violet c) remains at the same level d) microwave d) initially rises and then falls 188 The depletion layer opposes the flow of.. 182 When reverse bias is applied to a p-n junction a) majority charge carriers diode, the Fermi level in n-type ………….. with b) minority charge carriers respect to the Fermi level in p-type. c) both minority and majority charge carriers a) rises d) neither minority nor majority charge carriers b) falls c) remains at the same level 189 The part of a transistor, which is heavily doped d) initially rises and then falls to produce large number of majority carriers, i a) emitter b) base 183 When forward bias voltage is applied to a p-n c) collector d) any of the above junction diode, the width of the depletion depending upon the nature of transistor layer………….. a) increases 190 When a n-p-n transistor is used as an amplifier b) decreases then? c) remains constant a) the electrons flow from emitter to collector d) initially increases and then decreases b) the holes flow from emitter to collector c) the electrons flow from collector to emitter 184 When reverse bias voltage is applied to a p-n d) the electrons flow from battery to emitter junction diode, the width of the depletion layer………….. 191 If a transistor is to work as an amplifier, the a) increases emitter-base junction must be ………….. b) decreases a) forward biased c) remains constant b) reversed biased d) initially increases and then decreases c) not be biased d) any of the above 185 In a forward biased diode, the conduction is mainly due to …………….. 192 If a transistor is to work as an amplifier, the a) electrons collector-base junction must be ………….. b) holes a) forward biased c) electrons in p-type and holes in n-type b) reversed biased d) holes in p-type and electrons in n-type c) not be biased d) any of the above 186 In a reverse biased diode, the conduction is mainly due to …………….. 193 In an n-p-n transistor, …………..electrons from a) electrons emitter get neutralized in base. b) holes a) a large number of Government College of Engineering & Research, Awasari, MCQ’s by Smt. 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Chaudhari Page 14  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions b) very few a) in the direction of current c) all b) opposite to direction of current d) none of the c) either in or opposite to direction of current 194 The concentration of impurities in a transistor : d) perpendicular to direction of current a) equal for emitter, base and collector b) least for emitter region 201 In Hall effect voltage is developed …………….. c) largest for emitter region a) in the direction of current d) largest for collector region b) opposite to direction of current c) either in or opposite to direction of current 195 In an n-p-n transistor, …………..electrons from d) perpendicular to direction of current emitter cross over to collector. a) a large number of 202 If an electron moves along positive x axis and a b) very few magnetic field is applied in positive y direction, c) all the electron will experience a force along d) none of the ……………….. a) positive z b)negative z 196 In a biased n-p-n transistor, the Fermi level of x x emitter ………..with respect to that in base. c) positive d)negative a) remains at the same level b) shifts upwards 203 If a hole moves along positive x axis and a c) shifts downwards magnetic field is applied in positive y direction, d) first shifts up and then down the hole will experience a force along ……………….. 197 In a biased n-p-n transistor, the Fermi level of a) positive z collector ………..with respect to that in base. b) negative z a) remains at the same level c) positive x b) shifts upwards d) negative x c) shifts downwards d) first shifts up and then down 204 The Hall voltage is given by VH = … IBd Bd IqBd 198 The base of transistor is made thin and lightly a) b) c) doped because nqa Inqa na a) about 95% of the charge carriers may cross IBad d) b) about 100% of the charge carriers may cross nq c) the transistors can be saved from large currents 205 The Hall coefficient is given by RH = … d) none of these 1 n q a) nq b) c) d) 199 The Hall Effect voltage in intrinsic silicon is: nq q n a) Positive b) Zero 206 The Hall effect is used to determine ….. c) None of the above a) polarity of majority charge carriers d) Negative b) density of charge carriers c) mobility of charge carriers 200 In Hall effect, the magnetic field is applied d) all the above …………….. Government College of Engineering & Research, Awasari, MCQ’s by Smt. Y. N. Chaudhari Page 15  Engineering Physics UNIT 4: Semiconductor Physics Multiple Choice Questions 207 The Hall coefficient of an intrinsic semiconductor 213 The Hall coefficient of (A) at room temperature is: is 4×10–4 m3 coulomb–1. The carrier concentration a) Positive under all conditions in sample A at room temperature is: b) Negative under all conditions a) ~ 1021 m–3 c) Zero under all conditions b) ~ 1020 m–3 d) None of the above c) ~ 1022 m–3 d) None of the above -11 208 If the Hall coefficient of a material is 1.25 × 10 m3 / C and charge of an electron is 1.6× 10-19 C, 214 The generation of an e.m.f. across an open the density of electron is …………… per m3. circuited p-n junction when light is made a) 2×1029 b) 4×1029 c) 5×1029 incident on it is known as ………………effect. d) 2×1024 a) photoemissive b) photoconductive 209 Hall effect is observed in a specimen when it c) photovoltaic (metal or a semiconductor) is carrying current d) none of the above and is placed in a magnetic field. The resultant electric field inside the specimen will be in: 215 The output from a solar cell is …………… a) A direction normal to both current and a) a.c. magnetic field b) d.c. b) The direction of current c) can be either a.c. or d.c. c) A direction anti parallel to magnetic field d) none of the above d) None of the above 216 A solar cell consists of ……………. 210 When ne and nh are electron and hole densities, a) alkali metal and µe and µn are the carrier mobilities, the Hall b) pure semiconductor coefficient is positive when c) an extrinsic semiconductor a) nh µh >neµe d) p-n junction b) nh µh2> neµe2 c) nhµh