Semiconductor Electronics: Materials, Devices and Simple Circuits

Prof. G. Vijayendra SBM Jain College, V.V Puram

© G. Vijayendra, Prof. in Physics

Prof. G. Vijayendra SBM Jain College, V.V Puram

PHYSICS

Semiconductors have ρ higher than that of metals and have negative α i.e., their resistivity decreases with increase in temperature.

Synopsis

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Semiconductors have ρ higher than that of metals and have negative α i.e., their resistivity decreases with increase in temperature.

CLASSIFICATION OF SEMICONDUCTORS ON THE BASIS OF THE COMPOSITION

SEMICONDUCTORSSEMICONDUCTORS

Elemental semiconductor

Si Ge

Elemental semiconductor

Si Ge

Compound Semiconductor

Compound Semiconductor

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Elemental semiconductor

Si Ge

Elemental semiconductor

Si Ge

Compound Semiconductor

Compound Semiconductor

Inorganic CdS, GaAs, CdSe, InP

Inorganic CdS, GaAs, CdSe, InP

Organic anthracene polypyrrole polyaniline

Organic anthracene polypyrrole polyaniline

Metals:

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Insulators:

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Semiconductors:

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SemiconductorsSemiconductors

Intrinsic semiconductor

Intrinsic semiconductor

Extrinsic Semiconductor

Extrinsic Semiconductor

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Intrinsic semiconductor

Intrinsic semiconductor

Extrinsic Semiconductor

Extrinsic Semiconductor

n–type semiconductor

n–type semiconductor

p–type semiconductor

p–type semiconductor

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 or Ge with a pentavalent dopant like phosphorus.

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P–type semiconductor This is obtained by doping pure semiconductors like Ge or Si with a trivalent impurity like aluminium.

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p-n junction under forward 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 of small change in voltage (V) to the corresponding change in current (I)

..............d V

r I

   

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..............d V

r 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 characteristics Reverse bias

OPTOELECTRONIC JUNCTION DEVICES

Optoelectronics is the study and application of electronic devices that source, detect and control light. Some of the optoelectronic devices are photodiodes, light emitting diodes and solar cells (photovoltaic cells).

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OPTOELECTRONIC JUNCTION DEVICES

Optoelectronics is the study and application of electronic devices that source, detect and control light. Some of the optoelectronic devices are photodiodes, light emitting diodes and solar cells (photovoltaic cells).

Photodiode

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LIGHT EMITTING DIODE (LED) LED is a heavily doped p-n junction which under forward bias emits spontaneous radiation.

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

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TRANSISTOR It has three doped regions namely emitter, base and collector.

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Emitter: It is moderate in size and heavily doped. It supplies large number of majority charge carriers. Collector: It is larger in size compared to emitter and is moderately 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 oscillator An oscillator is an electronic device which produces sustained electrical oscillations (ac signal) of constant frequency and amplitude without any external input.

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

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Transistor as an oscillator An oscillator is an electronic device which produces sustained electrical oscillations (ac signal) of constant frequency and amplitude without any external input.

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

OR gate

Truth Table: OR gate

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Truth Table: OR gate A B y=A+B 0 0 0 0 1 1 1 0 1 1 1 1

AND gate:

Truth Table: AND gate

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Truth Table: AND gate A B y=A.B 0 0 0 0 1 0 1 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 gate A B 0 0 1 0 1 0 1 0 0 1 1 0

y A B 

NAND gate:

Truth table: NAND gate

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Truth table: NAND gate A B 0 0 1 0 1 1 1 0 1 1 1 0

.y A B

1. Electrical conductivity in a semiconductor is due to 1. electrons only 2. free electrons and ion cores. 3. free electrons and holes 4. ion cores and holes

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Answer: 3 both free electrons and holes are charge carriers

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

3. The movement of a hole is brought about by 1. the vacancy being filled by a free electron. 2. the vacancy being filled by a valence electron from a

neighbouring atom 3. the movement of an atomic core 4. the movement of a free electron in the valence band

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3. The movement of a hole is brought about by 1. the vacancy being filled by a free electron. 2. the vacancy being filled by a valence electron from a

neighbouring atom 3. the movement of an atomic core 4. the movement of a free electron in the valence band

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

4. A p-type semiconductor is 1. positively charged 2. negatively charged 3. electrically neutral 4. an insulator at room temperature

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

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

2. 106 : 1 3. 103 : 1 4. 1 : 108

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

2. 106 : 1 3. 103 : 1 4. 1 : 108

Answer: 2 106 : 1

6. An n-type and a p-type semiconductor can be obtained by doping pure silicon respectively with 1. arsenic and phosphorus 2. indium and aluminium 3. phosphorus and indium 4. aluminium and boron

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6. An n-type and a p-type semiconductor can be obtained by doping pure silicon respectively with 1. arsenic and phosphorus 2. indium and aluminium 3. phosphorus and indium 4. aluminium and boron

Answer: 3 n-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 room temperature are cooled to 90K. The resistance of 1. both will increase 2. both will decrease 3. copper increases while that of germanium decreases 4. copper decreases while that of germanium increases.

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7. A piece of copper and a piece of germanium at room temperature are cooled to 90K. The resistance of 1. both will increase 2. both will decrease 3. copper increases while that of germanium decreases 4. copper decreases while that of germanium increases.

8. Identify the incorrect statement 1. The forbidden gap in case of silicon is 1.12eV 2. The energy gap in germanium is 0.72eV 3. The conductivity of silicon will be more than that of

germanium at room temperature 4. When silicon is doped with