semiconductor Flashcards
Define energy gap or band gap. Write the unit in which band gap is
measured.
The energy difference between the top of the valence band and bottom of
the conduction band is called the energy band gap (Energy gap Eg ).
It is measured in electron volt
What are Intrinsic Semiconductors?
Pure semiconductors are called ‘intrinsic semiconductors’.
ne = nh = ni
.What are Extrinsic Semiconductor?
When a small amount of a suitable impurity is added to the pure
semiconductor, the conductivity of the semiconductor is increased . Such
materials are known as extrinsic semiconductors or impurity
semiconductors. There are two types of extrinsic semiconductors –
(i) n-type semiconductor
(ii) p-type semiconductor
What is doping and dopants?
The deliberate addition of a desirable impurity is called doping and the
impurity atoms are called dopants. Such a material is also called a doped
semiconductor
What are n-type semiconductors?
n-type semiconductor is obtained by doping Si or Ge with pentavalent
atoms (donors) like Arsenic (As), Antimony (Sb), Phosphorous (P),etc.
For n-type semiconductors, ne»_space; nh
What are p-type semiconductors?
p-type semiconductor is obtained when Si or Ge is doped with a trivalent
impurity like Indium (In), Boron (B), Aluminium (Al), etc.
For p-type semiconductors, nh»_space; ne
How a p-n junction is formed?
.
A p-n junction can be formed by adding a small quantity of pentavalent
impurity to a p-type semiconductor or by adding a small quantity of
trivalent impurity to an n-type semiconductor
What is Diffusion current?
The holes diffuse from p-side to n-side (p → n) and electrons diffuse from nside to p-side (n → p). This motion of charge carriers give rise to Diffusion
current across the junction.
.What is drift?
The motion of minority charge carriers across p-n junction due to
electric field is called called drift
What is Depletion region (Depletion layer)
The space-charge region on either side of the junction together is known as
depletion region. The depletion layer consist of immobile ion-cores and no
free electrons or holes. This is responsible for a junction potential barrier.
Barrier Potential
The loss of electrons from the n-region and the gain of electron by the pregion causes a difference of potential across the junction of the two
regions. Since this potential tends to prevent the movement of electron
from the n region into the p region, it is called a barrier potential.
The barrier potential of a Ge diode is 0.2Vand that of a Si diode is 0.7V.
What is forward biasing of a p-n junction diode ?
If p-side of the diode is connected to the positive terminal and n-side to the
negative terminal of the battery, it is said to be forward biased.
Write specific features of forward biased p-n junction diode.
▪ The depletion layer width decreases and the barrier height is reduced.
▪ The effective barrier height is (V0 – V ).
▪ The motion of majority carriers on either side gives rise to diffusion
current.
▪ The magnitude of this current is usually in mA
What is reverse biasing of a p-n junction diode ?
If n-side of the diode is connected to the positive terminal and p-side to the
negative terminal of the battery, it is said to be reverse biased.
Write specific features of reverse biased p-n junction diode.
▪ The depletion layer width increases and the barrier height is
increased.
▪ The effective barrier height is (V0 + V )..
▪ The drift of minority carriers gives rise to drift current.
▪ The drift current is of the order of a few μA.
