The output of the AND gate is Y = A.B consequently the input of the OR gate are A and A.B . Then the final Y = A + A.B

For faster action NPN Transistor is used. In an NPN transistor, current conduction is mainly by free electron, whereas in PNP type transistor. It is mainly holes Since electron are more mobile than holes we prefer NPN for faster action as well as high conduction current.

Mobility of an electron is defined as the drift velocity of electron per unit electric field
i.e \({ \mu }_{ e }={ V }_{ e }/E\)
Mobility of a hole is defined as the drift velocity of hole per unit electric field,
i.e,  \({ \mu }_{ h }={ V }_{ h/E }\)
The electrical conductivity \(\sigma \) =1.p =e \(\left( { n }_{ e }{ \mu }_{ e }+{ \mu }_{ h }{ \mu }_{ h } \right) \) where ne & n_h are free electron density & hole density respectively

(i) Main use of photodiode In demodulation optical signal and detection of optical signal. In light operated switches, electronic counters.
(ii) Main use of Zener diode As DC voltage regulator.

Zener diode
Alternatively


After the breakdown voltage, there is an insignificant change in the (reverse) bias voltage across the Zener diode (and hence the load) even for large changes in current.

As, car enters in the gate, any one or both are opened. The device is shown below:

So, OR gate gives the desired output

As, semiconductor A is doped with indium, so it behaves as p-type semiconductor and B is doped with arsenic so, it behaves as n-type semiconductor. Thus, the figure shows that it is forward bias condition.

The circuit resembles AND gate. The BOOLEAN expression of this circuit is, V₀ = A.B i.e. V₀ equals A AND B. The truth table of this gate is as given below:

When  \(p-n\) junction is reversed biased, the positive terminal of the external battery is connected to \(n-\)-side of  \(p-n\) junction and its negative terminal to  \(p\)-side  of  \(p-n\) junction. The positive terminal of the external battery attracts the majority carrier electrons from the \(n\)-region and its negative terminal attracts the majority carrier holes from \(p\)-region. Due to it, the majority charge carriers move away from the junction. This increases the width of the depletion layer.

When the temperature of the semiconductor is raised, more covalent bonds are broken in the given semiconductor. Due to it, there is a large increase in the charge carrier concentration in semiconductor. The fraction \((f)\) of the number of electrons raised from valence band to conduction band at temperature TK in intrinsic semiconductor is given by
\(f\propto e^{ -E_{ g }/2kT }\)
where \(E_{ g }\) is the value of forbidden energy gap. If means, if T increases, \(f\) also increases, i.e., with the increase in temperature, the number of electrons in conduction band increases. This leads to increase in conductivity of intrinsic semiconductor. As resistivity of pure semiconductor decreases with increase in temperature.

Here,\(E=1.14 \ eV=1.14\times 1.6\times 10^{ -19 } \ J\)
\(\\ \lambda =\frac { hc }{ E } =\frac { 6.62\times 10^{ -34 }\times 3\times 10^{ 8 } }{ 1.6\times 10^{ -19 }\times 1.14 } =10,888 \ A°\)