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Prepared by: Kenneth Joachim LlantoLast Updated: 22/06/11

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Conductors, Insulators and SemiconductorsExtrinsic SemiconductorsIntrinsic Semiconductors

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A material that allows the flow of current upon application of a small voltage

Materials with high electron mobility (manyfree electrons)

Best conductors have one valence electron

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silvercoppergold

aluminumironsteelbrassbronzemercury

graphitedirty waterconcrete

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The nucleus (neutrons and protons) and theinner orbits Valence (outer orbit) controls electricalpropertiesCopper atom core has net charge of +1

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A material that restricts the flow of current upon application of a voltage

materials with low electron mobility (few orno free electrons)

Commonly called dielectric materials

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glassrubberoil

asphaltfiberglassporcelainceramicquartz(dry) cotton

(dry) paper(dry) woodplastic

airdiamondpure water

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A material whose electrical properties fall between an insulator and a conductor

Three most frequently used semiconductorsare (Ge)Germanium, (Si)Silicon and (GaAs) Gallium Arsenide

Ge and SI have 4 valence electrons; Ga has 3 and As has 5 valence electrons

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Used during the first few decades of thediodes (1939) and transistors(1947)

Relatively easy to find and available in large quantities

Low reliability primarily due to sensitivity

changes in temperature

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Improved temperature sensitivity , but hard torefine to high purity levels at that time

1954, the first silicon transistor wasintroduced

One of the most abundant material on earth,

removing any problems with availability

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First transistor was developed in the 1970s

Provided a higher speed of operation , about 5times of Si

Hard to manufacture at high levels of purity ,hence was more expensive

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the band of energy occupied by the valence electrons. Hereelectrons are still bounded to the atomic structure

o Next higher permitted energy band. Electrons can move freely in this energy band

Gap between the valence band and conduction

band

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By thermal energy , some free electrons and holes are created

While other free electrons and holesrecombine.

The time between creation and recombination

of a free electron and a hole is called the life time .

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Intrinsic Semiconductors Semiconductors in their purest forms , free of

impurities

Extrinsic Semiconductors Semiconductors added with impurities called

dopant or doping agents

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Process of adding other materials calledimpurities to the silicon or germanium crystalto change its characteristicsThis is done to alter the electrical conductivity of the intrinsic semiconductor

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- Pentavalent materials :Antimony (Sb),Arsenic (As),Phosphorus (P)

PAsSb Has a valence of 5

Called donor atoms

Makes a n-typesemiconductor

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The addition of the pentavalent material creates afree electron which can be used for conduction

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- Trivalent materials :Boron (B), Gallium(Ga), Indium (In)

GaBIn Has a valence of 3

Called acceptor Atoms

Makes a p-type semiconductor

The addition of the trivalent material creates ahole in the structure, similar to that of a free electron

just in the opposite polarity

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N type Obtained when a pentavalent material is added

to pure silicon crystal. Has excess negative charge carriers Majority carriers are electrons and minority

carriers are holes

P type Obtained when traces of a trivalent material is

added to a pure silicon crystal. Has excess of positive charge carriers Majority carriers are holes and minority carriers

are electrons

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Conductors

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A. pure waterB. graphiteC. oilD.

fiberglassE. ceramicF. quartzG. air

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a. The nucleus

b. Neutrons and Protons

c. Inner orbits

d. Valence

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A. Silicon (Si)B. Gallium Nitride (GaN)C. Gallium Arsenide (GaAs)D.

Cadmium Sulfide (Cds)E. Germanium (Ge)

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N - type

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Holes

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Intrinsic Semiconductors in purest forms

ExtrinsicSemiconductors added with impurities called

dopants

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Doping

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Antimony (Sb)

Arsenic (As)

Phosphorus (P)Boron (B)Gallium (Ga)

Indium (In)

Pentavalent Trivalent

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