By going through these CBSE Class 12 Physics Notes Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits, students can recall all the concepts quickly.

## Semiconductor Electronics: Materials, Devices and Simple Circuits Notes Class 12 Physics Chapter 14

→ 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,
ne = nh = ni

→ 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 = $$\frac{1}{2 \pi \sqrt{\mathrm{LC}}}$$

→ Dynamic resistance of junction diode is given by
rd = $$\frac{\Delta \mathrm{V}}{\Delta \mathrm{I}}$$

→ Current flowing through the semiconductor is given by ”
I = Ie + Ih
= eA (ne μe + nh μh)

→ The conductivity of the semiconductor is given by
σ = e(ne μe + nh μh)

→ For intrinsic semiconductor, ne × nh = ni2
where ni = intrinsic carrier concetration, ne, nh are electron and hole carrier density.

→ Mobility is given by, μ = $$\frac{v_{\mathrm{d}}}{\mathrm{E}}$$
Ie = Ib + Ic

→ β = Ic/Ib = d.c current gain for CE. amplifier.

→ The α and β are related as
β = $$\frac{\alpha}{1-\alpha}$$

→ βac = $$\left(\frac{\Delta \mathrm{I}_{c}}{\Delta \mathrm{I}_{\mathrm{b}}}\right)_{\mathrm{V}_{\mathrm{ce}}=\mathrm{Constant}}$$

→ Voltage gain, AV = $$\frac{\Delta \mathrm{V}_{\mathrm{o}}}{\Delta \mathrm{V}_{\mathrm{i}}}$$ = Bac × $$\frac{\mathrm{R}_{\text {out }}}{\mathrm{R}_{\text {in }}}$$

→ Resistance gain = $$\frac{\mathrm{R}_{\mathrm{out}}}{\mathrm{R}_{\mathrm{in}}}$$

→ Power gain = $$\frac{\Delta P_{\mathrm{o}}}{\Delta \mathrm{P}_{\mathrm{i}}}=\frac{\Delta \mathrm{V}_{\mathrm{o}} \times \mathrm{I}_{\mathrm{o}}}{\Delta \mathrm{V}_{\mathrm{i}} \times \mathrm{I}_{\mathrm{i}}}$$
= Av × current gain

→ α = d.c. current gain for C.B. amplifier
= $$\frac{\mathrm{I}_{\mathrm{c}}}{\mathrm{I}_{\mathrm{e}}}$$

→ gm = Transconductance = $$\frac{\Delta \mathrm{I}_{\mathrm{c}}}{\Delta \mathrm{V}_{\mathrm{eb}}}$$
= $$\frac{\beta}{R_{\text {in }}}$$

→ Input resistance, ri = $$\left(\frac{\Delta V_{\mathrm{be}}}{\Delta \mathrm{I}_{\mathrm{b}}}\right)_{\mathrm{V}_{\mathrm{ce}}=\mathrm{Constant}}$$

→ Output resistance, r0 = $$\left(\frac{\Delta \mathrm{V}_{\mathrm{ce}}}{\Delta \mathrm{I}_{\mathrm{c}}}\right)_{\mathrm{I}_{\mathrm{b}}=\mathrm{Constant}}$$