2. • A solid atom ions or molecule packed closely and the
force that hold them in place give rise to distinctive
properties of various kind of solid.
• Most of solids are crystalline and Amorphous.
3. BAND THEORY
Band theory is the theoritical model explaing the state of electron in solid
material, that have value of energy only within certain specfic range.
Electron in an atom are presentbin different energy levels. When we
assemble a lattice of solid with N atom, then each level of an atom split
up into N levels in solid. This splitting up of sharp and tightly packed
energy level form Energy Band. The gap brtween adjacent bands
representing a range of energies that posses no electron called Band Gap.
4. Semiconductors.
Semiconductors are the material which have a conductivity between
conductors and non-conductors.
Gallium arsenide, germanium and silicon are some commonly used
semiconductor. Silicon is used in electronics circuit fabrication and
gallium arsenide used in solar cells, laser diodes etc.
5. INTRINSIC SEMICONDCTOR
Iemiconductor in which magnitude of the energy gap Eg is very small.
Some of the electron lying on the top of valence band gain efficient thermal energy even
at moderate temperature and get excited into conduction band leaving behind equal
number of holes in the valence band.These free electron and holes contributes to the
conduction of electricity.
To maintain a constant concentration of pairs rate of combination is proportional to rate of
generation.
B
Where k is proportionality constant takes into account the charge densities and properties of
the semicinductor material.
Now for pair generation
6. Conductivity of intrinsic semiconductors.
The electrical conductivity of a pure or perfect semiconductor crystal at any
temperature is due to intrinsic charge carriers, i e electrin and hole.
Substituting value of ni
If scattering dominated by phonon,
7. EXTRISIC SEMICONDUCTORS.
When a small quality of suitable impurity from group 5 of the periodic table is
added to pure material n-type semiconductor formed, where electron act as
majority charge carriers. Addition of group 3 element produce p- type
semiconductor, where holes are the majority charge carrier
The density of conduction electron Np can be assumed equal to density of
donar impurity atom.
The density of holes in the valance band NA is equal to the density of
acceptor atom.
Overall charge neutrality equation,
Bbbbbbbbbbb
By suitable simplification and substituion
8. These are the general equation for charge densities
Case 1 n- type semiconductor
Hole density,
10. CONDUCTIVITY EXTRINSIC
In an extrinsic either n or p type imuprity is present. Let us consider, n type
semiconductor the carrier concentration is expressed.
11. HALL EFFECT IN SEMICONDUCTORS.
IF a metal or semiconductor carrying a curren I is placed in a transverse
magnetic feild B, an electric feild E induced in the direction perpendicular
to both the direction of current and magnetic feild. This phenomenon is
called as Hall Effect. The electic feild produced is called as Hall Feild (Eh).
12. In an intrinsic semiconductor simultaneoualy both electron and holes are present.
These charges are differnt they move in the opposite direction in an electric feild.
Hall effect developed by the deflection of electron in the opposite direction to the
hall feild devwloped by the deflection of holes. Two charge fkow in the x direction
under the electric feild Ex, the current due to them,
(1)
Along y direction, the charges experience more than one feilds.
* Lorentz feild experienced by electron
* Lorentz feild experienced by holes
* Hall feild by both.
13. Since charge are not allowed to flow along the y direction, the current
Jy vanishes, ie Jy=0 in (2),-›ing Vex and Vbx from (3),
Further substituting the value of Ex,
15. Hall mobility,
Importance
• To determine carrier concentration (n)
• To determine type of semiconductor.
• To determine mobility of the charge carrier if conductivity of
of semiconductor is known
18. IMPORTANCE OF SEMICONDUCTORS
They are highly portable due to the smaller size.
Require less input power.
Longer life span.
Noise free while operating.
19. APPLICATION OF SEMICONDUCTOR.
Temperature sensors are made with semiconductor devices.
They are used in 3D printing machines.
Used in microchips and self driving cars.
Used in calculators, solar plates, computer and other electronic devices.
Transistor and MOSFET used as a switch in electrical circuits
Used as microcontroller, photo sensors, integrated chips.
