Semiconductor Electronics: Materials, Devices and Simple ... · Semiconductor Electronics:...

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Semiconductor Electronics: Materials, Devices and Simple Circuits Prof. G. Vijayendra © G. Vijayendra, Prof. in Physics Prof. G. Vijayendra SBM Jain College, V.V Puram PHYSICS

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Semiconductor Electronics:Materials, Devices and Simple Circuits

Prof. G. VijayendraSBM Jain College, V.V Puram

© G. Vijayendra, Prof. in Physics

Prof. G. VijayendraSBM Jain College, V.V Puram

PHYSICS

Semiconductorshave ρ higher than that of metals andhave negative α i.e., their resistivity decreases withincrease in temperature.

Synopsis

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Semiconductorshave ρ higher than that of metals andhave negative α i.e., their resistivity decreases withincrease in temperature.

CLASSIFICATION OF SEMICONDUCTORS ON THE BASISOF THE COMPOSITION

SEMICONDUCTORSSEMICONDUCTORS

Elementalsemiconductor

SiGe

Elementalsemiconductor

SiGe

CompoundSemiconductor

CompoundSemiconductor

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Elementalsemiconductor

SiGe

Elementalsemiconductor

SiGe

CompoundSemiconductor

CompoundSemiconductor

InorganicCdS, GaAs,CdSe, InP

InorganicCdS, GaAs,CdSe, InP

Organicanthracenepolypyrrolepolyaniline

Organicanthracenepolypyrrolepolyaniline

Metals:

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Insulators:

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Semiconductors:

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SemiconductorsSemiconductors

Intrinsicsemiconductor

Intrinsicsemiconductor

ExtrinsicSemiconductor

ExtrinsicSemiconductor

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Intrinsicsemiconductor

Intrinsicsemiconductor

ExtrinsicSemiconductor

ExtrinsicSemiconductor

n–typesemiconductor

n–typesemiconductor

p–typesemiconductor

p–typesemiconductor

Energy band diagrams of intrinsic semiconductors

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T = 0 K T > 0 K

N-type semiconductor

This is obtained by doping pure semiconductors like Si orGe with a pentavalent dopant like phosphorus.

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P–type semiconductorThis is obtained by doping pure semiconductors like Geor Si with a trivalent impurity like aluminium.

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p-n junction underforward bias

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p-n junction under reverse bias

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The dynamic resistance rd of a diode is defined as the ratio ofsmall change in voltage (V) to the corresponding change incurrent (I)

..............d

Vr

I

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..............d

Vr

I

Rectification

Half wave rectifier (HWR)

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Full wave rectifier (FWR)

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Zener diode

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I-V characteristicsReverse bias

OPTOELECTRONIC JUNCTION DEVICES

Optoelectronics is the study and application of electronicdevices that source, detect and control light. Some of theoptoelectronic devices are photodiodes, light emittingdiodes and solar cells (photovoltaic cells).

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OPTOELECTRONIC JUNCTION DEVICES

Optoelectronics is the study and application of electronicdevices that source, detect and control light. Some of theoptoelectronic devices are photodiodes, light emittingdiodes and solar cells (photovoltaic cells).

Photodiode

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LIGHT EMITTING DIODE (LED)LED is a heavily doped p-n junction whichunder forward bias emits spontaneousradiation.

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Solar Cell (photo voltaic cell)A solar cell is basically a p-n junctionwhich generates emf when solar radiationfalls on the p-n junction.

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TRANSISTORIt has three doped regions namely emitter, base and collector.

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Emitter: It is moderate in size and heavily doped. It supplies largenumber of majority charge carriers.Collector: It is larger in size compared to emitter and ismoderately doped.Base: It is the Central region which is very thin and lightly doped.

Transistor as a switch and amplifier

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Transistor as an oscillatorAn oscillator is an electronic device which produces sustainedelectrical oscillations (ac signal) of constant frequency andamplitude without any external input.

Principle of a transistor oscillatorAn oscillator may be regarded as a self-sustained transistoramplifier with a positive feedback. (In-phase feedback).

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Transistor as an oscillatorAn oscillator is an electronic device which produces sustainedelectrical oscillations (ac signal) of constant frequency andamplitude without any external input.

Principle of a transistor oscillatorAn oscillator may be regarded as a self-sustained transistoramplifier with a positive feedback. (In-phase feedback).

OR gate

Truth Table: OR gate

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Truth Table: OR gateA B y=A+B0 0 00 1 11 0 11 1 1

AND gate:

Truth Table: AND gate

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Truth Table: AND gateA B y=A.B0 0 00 1 01 0 0

1 1 1

NOT gate

Truth Table: NOT gate

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Truth Table: NOT gate

A y=Ᾱ

0 1

1 0

NOR gate:

Truth Table: NOR gate

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Truth Table: NOR gateA B0 0 10 1 01 0 01 1 0

y A B

NAND gate:

Truth table: NAND gate

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Truth table: NAND gateA B0 0 10 1 11 0 11 1 0

.y A B

1. Electrical conductivity in a semiconductor is due to1. electrons only2. free electrons and ion cores.3. free electrons and holes4. ion cores and holes

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Answer: 3both free electrons and holes are charge carriers

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Answer: 1intrinsically generated carriers are e-h pairs. Hence theirnumbers are equal.

3. The movement of a hole is brought about by1. the vacancy being filled by a free electron.2. the vacancy being filled by a valence electron from a

neighbouring atom3. the movement of an atomic core4. the movement of a free electron in the valence band

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3. The movement of a hole is brought about by1. the vacancy being filled by a free electron.2. the vacancy being filled by a valence electron from a

neighbouring atom3. the movement of an atomic core4. the movement of a free electron in the valence band

Answer: 2hole moves opposite to the direction of electron motion.

4. A p-type semiconductor is1. positively charged2. negatively charged3. electrically neutral4. an insulator at room temperature

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Answer: 3Any extrinsic semiconductor is electrically neutral becausewhile doping, only atoms are added.

5. The ratio of the number of host atoms to that of impurityatoms in a doped semiconductor can be1. 1 : 106

2. 106 : 13. 103 : 14. 1 : 108

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5. The ratio of the number of host atoms to that of impurityatoms in a doped semiconductor can be1. 1 : 106

2. 106 : 13. 103 : 14. 1 : 108

Answer: 2106 : 1

6. An n-type and a p-type semiconductor can be obtained bydoping pure silicon respectively with1. arsenic and phosphorus2. indium and aluminium3. phosphorus and indium4. aluminium and boron

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6. An n-type and a p-type semiconductor can be obtained bydoping pure silicon respectively with1. arsenic and phosphorus2. indium and aluminium3. phosphorus and indium4. aluminium and boron

Answer: 3n-type is obtained by doping Si with pentavalent impurity.p-type is obtained by doping Si with trivalent impurity.

7. A piece of copper and a piece of germanium at roomtemperature are cooled to 90K. The resistance of1. both will increase2. both will decrease3. copper increases while that of germanium decreases4. copper decreases while that of germanium increases.

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7. A piece of copper and a piece of germanium at roomtemperature are cooled to 90K. The resistance of1. both will increase2. both will decrease3. copper increases while that of germanium decreases4. copper decreases while that of germanium increases.

8. Identify the incorrect statement1. The forbidden gap in case of silicon is 1.12eV2. The energy gap in germanium is 0.72eV3. The conductivity of silicon will be more than that of

germanium at room temperature4. When silicon is doped with arsenic its conductivity

increases

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8. Identify the incorrect statement1. The forbidden gap in case of silicon is 1.12eV2. The energy gap in germanium is 0.72eV3. The conductivity of silicon will be more than that of

germanium at room temperature4. When silicon is doped with arsenic its conductivity

increases

Answer: 3Eg(Ge) < Eg(Si)

9. The impurity atoms that can produce acceptor energy level inthe energy band diagram of an extrinsic semiconductor cannotbe1. boron2. antimony3. aluminium4. indium

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9. The impurity atoms that can produce acceptor energy level inthe energy band diagram of an extrinsic semiconductor cannotbe1. boron2. antimony3. aluminium4. indium

Answer: 2Acceptor impurity is trivalent-boron, aluminium, indium.

10. A pure semiconductor is doped with a donor impurity.1. The hole concentration decreases2. The electron concentration increases3. The hole concentration increases4. Both (1) and (2) are correct.

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Answer: 4Donor impurity increases free electron number and is alsoresponsible in decreasing hole number due to recombination.

11. A semiconducting device is connected in series with a batteryand a resistance. A current is found to pass through the circuit.If the polarity of the battery is reversed, the current drops toalmost zero. The device may be1. an intrinsic semiconductor2. a p-type semiconductor3. an n-type semiconductor4. a p-n junction

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11. A semiconducting device is connected in series with a batteryand a resistance. A current is found to pass through the circuit.If the polarity of the battery is reversed, the current drops toalmost zero. The device may be1. an intrinsic semiconductor2. a p-type semiconductor3. an n-type semiconductor4. a p-n junction

Answer: 4Forward biased p-n junction conducts, while reverse biasedp-n junction does not conduct.

12. Let H be the effective height of the potential barrier and W bethe width of the depletion layer in a p-n junction.When the p-n junction is1. forward biased, H decreases while W increases2. forward biased, both H and W will decrease3. forward biased, both H and W will increase4. reverse biased, H decreases while W increases

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12. Let H be the effective height of the potential barrier and W bethe width of the depletion layer in a p-n junction.When the p-n junction is1. forward biased, H decreases while W increases2. forward biased, both H and W will decrease3. forward biased, both H and W will increase4. reverse biased, H decreases while W increases

Answer: 2During forward bias barrier height and junction depletionlayer width decreases. During reverse bias they increase.

13. The ratio of the concentration of electrons and holes in asemiconductor is 7:5 and the ratio of their currents is 7:4.Then the ratio of their drift velocities is1. 4:72. 4:53. 5:84. 5:4

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13. The ratio of the concentration of electrons and holes in asemiconductor is 7:5 and the ratio of their currents is 7:4.Then the ratio of their drift velocities is1. 4:72. 4:53. 5:84. 5:4

Answer: 4I = neAv

I 7 5 5v

4 7 4e e h

h h e

v I n

n v I n

14. The depletion layer in the p-n junction region is caused by1. drift of holes2. diffusion of charge carriers3. migration of impurity ions4. drift of electrons

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Answer: 2Diffusion is responsible for the depletion region.

15. The arrangement of gates given below represents

1. AND gate2. OR gate3. NAND gate4. NOR gate

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Answer: 1NAND followed by NOT is equivalent to AND gate

15. The arrangement of gates given below represents

1. AND gate2. OR gate3. NAND gate4. NOR gate

16. The output states X and Y respectively in the fig. shown1. 1,02. 0,13. 0,04. 1,1

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Answer: 2

17. A Zener diode is used for1. rectification in reverse bias mode2. voltage regulation in forward bias mode3. voltage regulation in reverse bias mode4. modulation in forward bias mode

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Answer: 3Zener diode as voltage regulator operates in reverse biascondition in breakdown region.

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19. The dominant mechanisms for the motion of charge carriersin forward and reverse biased silicon p-n junctions are1. drift in forward bias, diffusion in reverse bias2. diffusion in forward bias, drift in reverse bias3. diffusion in both forward and reverse bias4. drift in both forward and reverse bias

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19. The dominant mechanisms for the motion of charge carriersin forward and reverse biased silicon p-n junctions are1. drift in forward bias, diffusion in reverse bias2. diffusion in forward bias, drift in reverse bias3. diffusion in both forward and reverse bias4. drift in both forward and reverse bias

Answer: 2In forward bias - diffusionIn reverse bias - drift

20. When the voltage drop across a p-n junction diode isincreased from 0.65V to 0.7 V, the change in the diodecurrent is 5mA. The dynamic resistance of the diode is1. 20Ω2. 50Ω3. 10Ω4. 5Ω

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20. When the voltage drop across a p-n junction diode isincreased from 0.65V to 0.7 V, the change in the diodecurrent is 5mA. The dynamic resistance of the diode is1. 20Ω2. 50Ω3. 10Ω4. 5Ω

Answer: 3

3

0.7 0.65 0.0510

5 10 0.005f

Vr

I

21. Carbon (C), silicon (Si) and germanium (Ge) have four valenceelectrons each. At room temperature which one of the followingstatements is most appropriate?1. The number of free electrons for conduction is significant

only in Si and Ge but small in C2. The number of free electrons is significant in C but small in Si & Ge3. The number of free electrons is negligibly small in all the

three4. The number of free electrons is significant in all the three

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21. Carbon (C), silicon (Si) and germanium (Ge) have four valenceelectrons each. At room temperature which one of the followingstatements is most appropriate?1. The number of free electrons for conduction is significant

only in Si and Ge but small in C2. The number of free electrons is significant in C but small in Si & Ge3. The number of free electrons is negligibly small in all the

three4. The number of free electrons is significant in all the three

Answer: 1Eg in C is quite large.

22. A diode (p-n junction) is used as a/an1. oscillator2. rectifier3. amplifier4. regulator

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Answer: 2p-n junction is suitable to act as rectifier

23. Of the diodes shown inthe following diagrams,which one is reversebiased?

1. 2.

3. 4.

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Answer: 2negative terminal of battery to p-sidepositive terminal to n-side – amounts to reverse bias

3. 4.

19. The current gain β of a transistor in common-emitter mode is40. To change the collector current by 160mA, the necessarychange in the base current is (at constant VCE)1. 40µA2. 4µA3. 4mA4. 40mA

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19. The current gain β of a transistor in common-emitter mode is40. To change the collector current by 160mA, the necessarychange in the base current is (at constant VCE)1. 40µA2. 4µA3. 4mA4. 40mA

Answer: 3160

440

c cB

B

I I mAI mA

I

26. When a transistor is used as an amplifier1. emitter-base junction is reverse biased while collector-base

junction is forward biased2. emitter-base junction is forward biased while collector-base

junction is reverse biased3. both the emitter-base junction and collector- base junction

are reverse biased4. both the emitter-base junction and collector-base junction

are forward biased

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26. When a transistor is used as an amplifier1. emitter-base junction is reverse biased while collector-base

junction is forward biased2. emitter-base junction is forward biased while collector-base

junction is reverse biased3. both the emitter-base junction and collector- base junction

are reverse biased4. both the emitter-base junction and collector-base junction

are forward biasedAnswer: 2

27. A photodiode1. operates only when it is forward biased2. usually is operated in reverse biased condition3. acts as a source of emf4. is used as a voltage regulator

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Answer: 2Percentage change in current is appreciable in reverse biasedcondition.

28. If De, Db and Dc represent the doping concentration of theemitter, base and collector regions respectively of a transistorthen1. De=Db=Dc

2. De<Db<Dc

3. De>Dc>Db

4. Dc>De>Db

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28. If De, Db and Dc represent the doping concentration of theemitter, base and collector regions respectively of a transistorthen1. De=Db=Dc

2. De<Db<Dc

3. De>Dc>Db

4. Dc>De>Db

Answer: 3

29. The following figure shows a logic gate circuit with two inputsA and B and the output C. The voltage waveforms of A, B and Care as shownThe logic circuit gate X is1. OR gate2. AND gate3. NAND gate4. NOR gate

AB

CXX

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Answer: 2

29. The following figure shows a logic gate circuit with two inputsA and B and the output C. The voltage waveforms of A, B and Care as shownThe logic circuit gate X is1. OR gate2. AND gate3. NAND gate4. NOR gate

30. 68 Two identical capacitors A and B are charged to samepotential ‘V’ and are connected in two circuits at t=0 as shownin the figure. The charges on the capacitor at time t=CR arerespectively (e: exponential)1) VC, VC2) VC, VC/e3) VC/e, VC4) VC/e, VC/e

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30. 68 Two identical capacitors A and B are charged to samepotential ‘V’ and are connected in two circuits at t=0 as shownin the figure. The charges on the capacitor at time t=CR arerespectively (e: exponential)1) VC, VC2) VC, VC/e3) VC/e, VC4) VC/e, VC/e

Thank you

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Thank youProf. G. Vijayendra

SBM Jain College, V.V Puram