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Solids and Semi Conductor Devices
High Yield Facts

1. The solids in which the atoms are arranged i
a definite, regular and long range order are said t
be crystalline, otherwise if the atoms are arrange
in indefinite, irregular and short range order, the
are called amorphous.
2. Amorphous substances are termed as glass
substances, since glass is an amorphous solid.
3. Crystalline solids are bounded by flat surface
and possess uniform chemical composition whil
the distribution of atoms or molecules in amorphou
solids are random and chaotic and they are no
bounded by flat surface.
4. Crystalline solids are anisotropic i.e. the physica
properties like thermal conductivity, electrica
conductivity, compressibility etc have different value
in different directions, while amorphous solids ar
isotropic.
5. Crystalline solids have a sharp melting poin
i.e. change of solid state occurs suddenly whil
the amorphous solids do not have this.
6. Below the temperature of crystallisation, th
crystalline solids are in a stable state, since a stabl
state is the state of minimum energy, such a materia
acquires a state of minimum energy on crystallisation
7. The infinite array of atoms or molecules in spac
such that each of the atom or molecule possesse
identical surroundings is called crystal lattice.
8. The smallest geometrical block consisting o
one or more atoms from which whole of the crysta
lattice may be built by translating the block, paralle
to itself in all directions is called the unit cell.
9. Mono crystal is a crystal in which the ordere
arrangements of the atoms or molecules extend
throughout the piece of solid, irrespective of it
size.
10. Poly crystal is a crystalline solid in which eac
piece of the solid has a number of mono crystal
with will developed faces joined together.
11. Some organic crystalline solids, when heate
acquire fluidity but retain their anisotropic properties
They are called liquid crystal.

12. Some liquid crystals like cyanobiphenyl can
change the plane of polarisation of light and such
liquid crystal displays (LCD) are used in watches
and micro calculator.
13. The polycrystal ceramic made from PbO, ZnO
2
and TiO are used in gas lighter, and telephone
2
receiver.
14. The cubic crystals may be of the form, simple
cubic lattice (Sc), the body centred lattice (bcc),
the face centred lattice (fcc).
15. The number of atoms in a crystal which surrounds
a particular atom as its nearest neighbours is called
co-ordination number.
16. The atomic radius is the distance between the
centres of two neighbouring atoms.
17. Atomic packing factor is the ratio of the volume
occupied by the atoms in a unit cell to the volume
of the unit cell.
18. Density of a crystalline solid is defined as the
ratio of the mass of the unit cell to the volume of
the unit cell.
19. The minimum amount of energy which must
be given to an electron so that it may escape from
the metallic surface is called the work function of
that surface.
20. When a very intense electric field, say
6
volt/cm is applied such as to make a metal
10
surface negative with respect to the space around
it, then some of the free electrons are accelerated
away from the surface. This is known as field emission
or cold emission.
21. Photo electric emission occurs when electrons
are emitted from metal surface on irradiating them
with radiation of suitable frequency.
22. When a highly energetic electron strikes the
surface of a metallic plate it usually causes the
emission of other electrons from the surface. The
electron striking the surface is called primary electron,
while those emitted from the surface are called
secondary electrons. This phenomenon is known
as secondary emission.

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