Physics M.C.Q (1 Marks)

When an impurity $($either a $p-$type atom or an n-type atom$)$ is doped into an intrinsic semiconductor, it increases the number of charge carriers in the intrinsic semiconductor. As conductivity is directly related to the number of charge carriers, the conductivity of a semiconductor increases with doping.

The valency of semiconductor $(Ge$ or $Si)$ is four, hence it has $4$ valence electrons in the outermost orbit of the $Ge$ or $Si-$atom

Holes are created when a co$-$valent bond is broken due to thermal energy. The removal of one electron leaves a vacancy known as a hole.

Integrated circuits or $I.C's$ are those semi-conductor device with both active and passive electronic elements diffused into a silicon water to form a functional circuit.

$p−n$ junction diode near threshold voltage is used as a square law device for modulation.

1. Depletion region : On account of difference in concentration of charge carrier in the two sections of $P-N$ junction, the electrons from $N-$region diffuse through the junction into $P-$region and the hole from $P$ region diffuse into $N-$region.

• The thickness of depletion layer is $1$ miscron $= 10^{-6} \mathrm{~m}$.
• Width of depletion $\text{layer}\propto\frac{1}{\text{Dopping}}$.
• Depletion is directly proportional to temperature.
• The $P-N$ junction diode is equivalent to capacitor in which the depletion layer acts as a dielectric.

2. Potential barrier: The potential difference created across the $P-N$ junction due to the diffusion of electron and holes is called potential barrier.