NCERT Solution Class 12th Physics Chapter – 14 Semiconductor Electronics Materials Devices And Simple Circuits Notes

NCERT Solutions Class 12th Physics Chapter – 14 Semiconductor Electronics Materials Devices And Simple Circuits

NCERT Solutions Class 12th Physics Chapter – 14 Semiconductor Electronics Materials Devices And Simple Circuits

?Chapter -14?

✍Semiconductor Electronics Materials Devices And Simple Circuits✍

?Notes?

A solid behaves like a good conductor if there is no forbidden gap.

A solid behaves as a semiconductor if its forbidden gap is small am behaves as an insulator if its bandgap is large.

In an intrinsic semiconductor, the electrical conductivity is determined only by thermally generated charge carriers. Their number is very small so the thermal conductivity is low.

Doping of semiconductors with a small amount of impurity changes their conductivity highly.

The majority of charge carriers in the p-type and n-type semiconductors are holes and electrons respectively.

Electron mobility is higher than that of holes.

At low temperatures, the free electrons remain in the V.B. of the semiconductor. As the temperature rises, electrons cross over to the conduction band.

Both n and p-semiconductors are neutral.

For an intrinsic semiconductor,
n_e = n_h = n_i

At higher temperatures, the conductivity of the semiconductor increases due to the increase in the number density of the charge carriers.

The potential barrier in the Ge diode is about 0.3 V and that of the Si diode is about 0.7 V.

Potential barrier opposes the forward current and supports the reverse current. ‘

The width of the depletion layer is of the order of 10^-6 m = 1 pm.

The electric field set up across the potential barrier is of the order of 3 × 10⁵ Vm^-1 for Ge and 7 × 10⁵ Vm^-1 for Si.

The current gain for CE configuration (β) ranges from 20 to 200.

For full wave rectifier, the minimum number of d iodes required is two.

The p-n junction can be assumed as a capacitor having the depletion layer acting as a capacitor.

Semiconductor devices are current controlled devices.

The semiconductor devices are temperature sensitive devices.

After the breakdown, the reverse current does not depend on the reverse voltage.

The junction diode has a unidirectional flow of current.

Due to unidirectional current characteristics a junction diode is used as a rectifier.

In a photodiode, light is made to fall on the junction so that current is proportional to the intensity of incident light.

The LED emits light energy due to recombination of electrons and holes at the junction.

In solar cell, sun’s energy is converted into electrical energy.

There are two junctions in a transistor. Emitter-base junction is always forward biased and the base-collector junction is always reverse biased.

The input resistance of the transistor is always lesser than that of
the output (collector) resistance.

α: It is always less than unity.

β > > α.

Common emitter configuration is most commonly used.

The energy in the tank circuit is alternatively stored in the electric field of the capactior and the magnetic field around the inductor.

In a binary number system only two numbers 0 and 1 are used.

Positive or high values are represented by 1 while the low values are represented by 0.

AND, OR and NOT gates are the basic gates.

NAND or NOR gates are called the basic building blocks of the digital circuits.

NAND gate – It is a combination of AND gate followed by a NOT gate.

NOR gate: It is the combination of OR gate followed by the NOT gate.

Dynamic resistance or a.c. resistance of a diode: It is defined as the ratio of the change in applied voltage to the change in the current of the diode.

Current gain – It is defined as the ratio of the output current to the input current.

 α – It is defined as the ratio of change in collector current to the change in emitter current.
β – It is the ratio of change in collector current to the change in base current.

Logic gate is a circuit which has one or more than one inputs and only one output.

AND gate – It is the logic curcuit in which the output is high if both the inputs are high and the output is low if one or both the inputs are low.

OR gate – It is a logic circuit having output high if one or both the inputs are high and the output is low if both the inputs are low.

NOT gate – It has high output if input is low and vice-versa.

Important Formulae

Frequency of L.C. oscillation is given by
v = 12πLC√

Dynamic resistance of junction diode is given by
r_d = ΔVΔI

Current flowing through the semiconductor is given by ”
I = I_e + I_h
= eA (n_e μ_e + n_h μ_h)

The conductivity of the semiconductor is given by
σ = e(n_e μ_e + n_h μ_h)

For intrinsic semiconductor, n_e × n_h = n_i²
where ni = intrinsic carrier concetration, ne, nh are electron and hole carrier density.

Mobility is given by, μ = vdE
I_e = I_b + I_c

β = I_c/I_b = d.c current gain for CE. amplifier.

The α and β are related as
β = α1−α

β_ac = (ΔIcΔIb)Vce=Constant

Voltage gain, AV = ΔVoΔVi = B_ac × Rout Rin 

Resistance gain = RoutRin

Power gain = ΔPoΔPi=ΔVo×IoΔVi×Ii
A_v × current gain

α = d.c. current gain for C.B. amplifier
= IcIe

g_m = Transconductance = ΔIcΔVeb
= βRin 

Input resistance, r_i = (ΔVbeΔIb)Vce=Constant

Output resistance, r₀ = (ΔVceΔIc)Ib=Constant