CHAPTER 1 [Compatibility Mode]

CHAPTER 1INTRODUCTION

TO SEMICONDUCTORS

2/5/20131

EE201 SEMICONDUCTOR DEVICES

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OBJECTIVES

1. The basic structure of an atom2. Atomic structure affects the flow of

material.3. Features and electrical properties of

semiconductors.4. What type of semiconductor material-N

and P-type produced

FIRST OBJECTIVES :-

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Struktur asas bagi atomThe basic structure of an atom

ATOMIC STRUCTURE

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Jirim terdiri daripada atom.

Each atom consists ofi. protonii. electroniii. neutron

ATOMIC STRUCTURE

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• The properties of electrons, protons and neutrons: -i. Electron- Electrons are particles of the lightest and smallest.- Each electron has a negative charge of equal size.- Always move at high speed around neukleus

ATOMIC STRUCTURE

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The properties of electrons, protons and neutrons: -ii. Proton - Proton is estimated to be 1800 times greater than the electron- Bringing positive charge equal

ATOMIC STRUCTURE

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The properties of electrons, protons and neutrons: -iii. Neutron -The mass of a neutron approximately equal to the mass of a

proton- No lead no charge- neutral charge

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ATOMIC STRUCTURE

NukleusAwan elektron+

+ +

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ATOMIC STRUCTURE HYDROGEN

Contains only one proton

+proton

electron

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Neucleus atom: - carbon - 6 proton 6 neutron copper - 29 protons, 29 neutronsAluminium - 13 protons, 13 neutrons Silicon - 14 protons, 14 neutronsGermanium - 32 protons, 32 neutrons

ANOTHER ATOMIC STRUCTURE

Atomic Structure

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In the atom there is a maximum of 7 layers orbit (shell)

Each layer is known as the layer K, L, M, N, O, P and Q

The maximum number of electrons in an orbit determined by the formula:

2 x n² n is the number of layers position

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Maximum number for each layer are:Shell K (1) : 2n x 1² = 2Shell L (2) : 2n x 2² = 8Shell M (3) : 2n x 3² = 18Shell N (4) : 2n x 4² = 32Shell O (5) : 2n x 5² = 50Shell P (6) : 2n x 6² = 72Shell Q (7) : 2n x 7² = 98

Method to determine the number of electrons in each shell

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Examples of Atom Structure

+13 2 + 8 + 3 = 13

Layer K = 2 electron

Layer L =

8 elektron

Layer M = 3elektron

Aluminium = 13 electron

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The outermost layer of atoms for something - valence shell

shell is not more than 8 valence electrons

Electrons in this shell - valence electron

Numbers valence electrons determine the electrical properties of the material things

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Trivalent atom.

Has 3 valence electronsExample: -

Indium, Boron and Aluminum

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Pentavalent atom.

Has 5 valence electrons

Example: -Antimony (Sb), arsenic (As)

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Neutral atoms: -

Total number of protons in the nucleus equals the number of electrons in the electron cloud. .

SECOND OBJECTIVES :-

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Atomic structure affects the flow of material

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Materials that allow the flow of charge / current when a voltage

source for many specific magnitude applied between the

two terminals

i.i. CONDUCTORCONDUCTOR

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1. Can conduct electricity2. Low resistance - easy current flow3. Atomic valence electrons are more likely to release4. Become free electrons move from one atom to

another.

Have one to three valence electrons

ii. Conductor Characteristics

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Material that does not allow any current flow

through

ii.ii. INSULATIONINSULATION

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1. Electric current can not flow2. Have high resistivity3. Receiving atomic valence electrons of atoms to

fill the other valence layer and make it stable & capable atom Set as escape from any electrical activity @ chemical

Have 5 to 8 valence electrons

ii. Insulation Characteristics

iii. SEMICONDUCTOR

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A material with a level of extreme thermal insulators

and conductors

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Has 4 valence electrons

1. The situation is intermediate conductor and insulator

2. Not easy to remove / receive valence electrons of other atoms

iii. Semiconductor Characteristics

Silicon and Germanium as an example of semiconductor

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1432

Layer (M) –

Valens Layer = 4

Layer (N) –

Layer Valens = 4

Layer (K) = 2 x 1 = 2

Layer (L)

2 x 4 = 8

Layer (M)

2 x 9 = 18

No. atom Germanium = 32

2 + 8 + 18 + 4 = 32No.atom silikon = 14

2 + 8 + 4 = 14

Bond Covalent

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Sharing of valence electrons of an atom with valence electrons of neighboring atoms makes an atom is in a stable condition

Si Si

Si Si Si

Si

Si Si Si

Figure of Bond Covalent

THIRD OBJECTIVES :-

FEATURES SEMICONDUCTOR TYPE - N and Type - P

MATERIAL N

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When semicondutor @ Silicon Germanium doped with impurities pentavalent (Arsenic), occurring over one electron.Semiconductor becomes more electronThis material is call material N

Si Si

Si As Si

Si

Si Si Si

Figure of Bounded Convalent

Excess of 1 electron

MATERIAL P

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When semicondutor @ Silicon Germanium doped with impurities trivalent (Indium) shortage, 1 pair.Holes exist charged + veThis becomes more holes

Semiconductor This material is call material P

Si Si

Si In Si

Si

Si Si Si

Figure of Bounded Convalent

Less than 1 pair of electrons

Characteristics of Material P

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Semiconductor doped with impurities that have 3 electrons ValenceMajority current carriers are holesMinority current carriers are

electrons

Material p

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Semiconductor doped with impurities that have five electrons ValenceMajority current carriers are electronsMinority current carriers are holes

Material N

Characteristics of Material N

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The sequence of events when the junction is formed

Material N

Material P

Characteristics of Material P-N Junction

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Depletion Region

Barrier voltagei. Germanium = 0.3Vii. Silicon = 0.7V

N-type P-type


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Electrons in the N material are attracted to fill the holes, holes in P type material

Crossings occur electrons from N-type material to the P-type material



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This combination makes the electron-holes near grafting atoms become neutral.

After some time existed an area that no longer have current carriers.



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Electron crossing stop.

The area around it is known as the depletion area.



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There is little resistance between two materials together due to the formation of depletion region

Resistance small value



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Also there is a difference in potential between the two materials - known as Voltage Barrier.

Barrier voltage for: -- Germanium = 0.3V- Silicon = 0.7V

Characteristics of Material P-N JunctionThe sequence of events when the

junction is formed

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1. Bias Voltage

Define :-

Bias voltage is applied voltage across combination of P-N

There are two types of bias: -i)Forward biasii)Reverse bias

i. Forward bias

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Define :- Negative source is connected to the N-type

material and Positive causes connected to the P-type material

1. Bias Voltage

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i. The losses become narrow area.ii. low resistivityiii. Current can flow through it

BENDA N BENDA P

1. Bias Voltage

i. Forward bias

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Define :-

N-type material to get the supply voltage is + ve and P type of

material gets voltage - ve

ii. Reverse bias

1. Bias Voltage

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i. The losses become wider area.ii. Resistivity is highiii. Not allow current to flow through it

BENDA N BENDA P

1. Bias Voltage

ii. Reverse bias

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Minority current within the material.

Exists when the PN grafts given bias voltage inverting.

The electrons in the p-type material will be rejected by the bias voltage to the grafts, and crosses

2. LEAKAGE CURRENT

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Resulting value of the current flow is very small. This current is referred to as Leakage current or

reverse current Its value depends on the temperature. The lower the

temperature, the lower the value, and vice versa.

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2. LEAKAGE CURRENT

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If the PN grafts reverse bias voltage applied is too high, it will disrupt the stability of the covalent bond.

Elektrons will be attracted to the positive ability and free as current carriers.

3. Point Breakdown

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This liberated electrons would violate the ties of others.

Ensued a reverse current flow is very high value

Extent of the increase in current which suddenly is called breakdown point

3. Point Breakdown

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It can cause burns grafting P-N.

Voltage at the point of breakdown or (breakdown voltage) to a maximum voltage that can be biased inverse grafting.

3. Point Breakdown

Documents

CHAPTER 1 [Compatibility Mode]