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Solid State Materials and Devices

Text Books

• Solid state Electronic Devices(7th edition - 2014)

By Ben G. Streetman & Sanajay Banerjee

• Semiconductor device fundamentals(2nd edition – 1996)

By Robert F. Pierette

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Matter

Solids • Rigid and incompressible

• Definite shape

• Definite mass

• Definite volume

• High density.

• Strong intermolecular forces

• Short inter nuclear distance due to close packing of constituent particles.

• Atoms vibrate about their fixed position

• No translator motion but oscillate only around their mean position

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Classification of Solids

• Crystalline Solids

• Amorphous Solids

Crystalline Solids • ion, molecule or atoms are arranged in definite geometric pattern

in the three dimensional network • arrangement repeats periodically over the entire crystal bounded by PLANES or FACES • Planes intersect at particular angles • Have characteristic geometrical shape • properties like electrical conductance, refractive index, thermal

expansion, etc., have different values in different directions • give a clean surface after cleaving it with a knife rather than an

irregular breakage • have sharp melting and boiling points • Examples: • Copper Sulphate (CuSO4), NiSO4, Diamond, Graphite, Si,NaCl, Sugar

etc

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Basic crystal structures

Classification of crystalline solids

• Classified on the basis of type of constituent particles and the nature of

intermolecular forces between them.

– Ionic solid

– Molecular Solids

– Covalent or Network Solids

– Metallic Solids

• Ionic Solids

• constituent particles are anions and cations-Each participating ion is

surrounded by a typical number of opposite charges

• high melting point and boiling point due to strong electrostatic force of

attraction

• behave like insulator but in an aqueous solution, they are good conductors

of electricity because the ions become free.

• They are hard and brittle because their stability depends upon the

preservation of their geometric pattern.

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• Example, in NaCl crystal,

– each Na+ ion is surrounded by 6 Cl- ions and each Cl- ion is

surrounded by 6 Na+ ions.

– the coordination number of Na+ and Cl- is 6.

– These ions are held together with strong electrostatic force of attraction.

• Molecular Solids

• particles are molecules

• Depending upon the nature of the molecules they are further divided into three types.

• Due to this weak force, they have low melting and boiling points, are soft in nature and non-conductors of electricity (no ions are present).

• They are generally gaseous or liquid in nature at room temperature and pressure.

– Non Polar Molecular Solids

– Polar Molecular Solids

– Hydrogen-bonded molecular solids

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Covalent or Network Solids

• constituent particles are atoms of the same or different elements connected to each other by covalent bond.

• a network of covalent bonds is formed throughout the crystal and they form a giant molecule.

• Due to strong covalent bonds, they are hard and brittle

• high melting and boiling points

• Example is diamond, silicon carbide (SiC) and graphite, etc.

• They are insulators but graphite is exception in this case because of the free fourth electron of each carbon atom where each carbon atom is linked to three neighboring carbon atoms. So graphite is good conductor of electricity.

• Metallic Solids

• contain metal atoms as constituent particles

• have a good tendency to lose their valence electron and change in to positively charged metal ions

• Their electrons can easily move throughout the whole crystal and form the sea of free electrons

• attractive force between the ions and mobile valence electrons is termed as metallic bond.

• Because of these strong metallic bonds, metals can maintain a regular structure and usually have high melting and boiling points.

• Metals have high electrical and thermal conductivity because the free electrons flow with a charge or heat energy through the metal

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Two distinct Classes of Solids

• Amorphous Solids

– non-crystalline solid

– lacks the long-range order characteristic of a crystal

– particles are randomly arranged in three dimension

– don’t have a definite geometrical shape

– don’t have sharp melting points.

– formed due to sudden cooling of liquid.

– melt over a wide range of temperature

– Coal, Coke, Glass, Plastic, rubber etc

Insulators, conductors, Semiconductors

• Insulators

– Do not permit electrons to flow freely from particle to particle

– Do not permit charge to be transferred across the entire surface of the object

– Offer very resistance to the flow of current

Material Resistivity (ohm m)

Glass 1012

Mica 9 x 1013

Quartz (fused) 5 x 1016

copper 1.8 x 10-8

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Insulators, conductors, Semiconductors

• Conductors

– permit electrons to flow freely from particle to particle

– permit charge to be transferred across the entire surface of the object

– Charge transport via hopping of carriers

Insulators, conductors, Semiconductors

• Semicondutor

– can conduct electricity under some conditions but not under others

– make a good medium for the control of electrical current

– Conductivity varies depending

• Temperature

• Doping

• Applied voltage

• Intensity of irradiation i.e. infrared , visible light, ultraviolet , or X rays

– Can absorb light

– Can emit light

– Current transfer can be via

• Hopping of carriers

• Tunneling of carriers

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Periodic Table of the Elements

Semiconductors

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Compound Semiconductors

Elemental and Compound Semiconductors

• Elemental – Silicon, Germanium

• Compound

– Binary AlAs, GaN, InP,GaAs, GaP, InP

– Ternary AlGaAs, GaAsP

– Quaternary InGaAsP, AlGaAsSb