Revision: Electronic Components/ Study of Components and Circuits Computer Science 2 HSC Science (Computer Science) 11th Standard Maharashtra State Board

• When n-type and p-type semiconductor materials are fused together, the junction formed is called a p-n junction.
• The device obtained by growing a p-type semiconductor over an n-type semiconductor or vice versa is called a p-n junction.

A p-n junction when provided with metallic connectors on each side is called a junction diode.

• The formation of a narrow region on either side of the junction which becomes free from mobile charge carriers is called depletion region.
• The small charge-free region formed near the junction where electrons combine with holes is known as the depletion region.

The difference in potential that prevents charge carriers from moving across the p-n junction is called the potential barrier.

The current flowing from p-side to n-side due to diffusion of electrons and holes because of concentration difference is called diffusion current.

The current flowing from n-side to p-side due to holes and electrons created in the depletion region is called drift current.

When a semiconducting material such as silicon or germanium is doped with a trivalent impurity on one side and pentavalent impurity on the other side, a p-n junction is obtained. The plane separating the two regions is called a junction.

The resistance offered by a p-n junction diode when it is in forward biased condition is called static (DC) resistance.

The resistance of a diode at a particular applied voltage is called dynamic (AC) resistance.

When a high reverse voltage causes a sudden and uncontrollable increase in current, the phenomenon is called avalanche breakdown.

• A rectifier that consists of one p-n junction diode in which alternate pulses of AC input are rectified, having a maximum efficiency of 40.6% and output frequency the same as that of input, is called a Half-Wave Rectifier.
• A rectifier which rectifies only one-half of each AC input supply cycle is called a half-wave rectifier.

\[E=\frac{V_b}{d}\]

Where:

• \[V_b\]​ = potential barrier
• d = width of the depletion layer
• E = electric field intensity

r_a = \[\frac {ΔV}{ΔI}\]

It is the reciprocal of the slope of the I-V characteristics at that point.

• Size & Weight: Semiconductor devices are smaller in size and lightweight, which also enables faster speed of operation.
• Power Consumption: They operate at small voltages (few mV) and require very less current (µA or mA), hence consume lesser power and produce almost no heating effects — making them thermally stable.
• Controllability: The electronic properties of semiconductors can be controlled to suit our requirement, and fabrication of ICs is possible.
• Sensitivity: They are sensitive to electrostatic charges, radiation, and fluctuations in temperature — making them fragile in harsh environments.
• Limitations: They are not useful for controlling high power, require controlled conditions for manufacturing, and very few materials are semiconductors.

• At a p-n junction, donor impurity atoms become positively charged ions and acceptor atoms become negatively charged ions — these act like two electrodes forming a p-n junction diode.
• A strong electric field, directed from the n-type to the p-type semiconductor, exists at the junction.
• Within the depletion layer, only immobile positive and negative ions are present; material outside remains neutral.
• The potential barrier is influenced by the type of semiconductor crystal, temperature, and the level of doping.
• If the diode is ON, it has no voltage across it and acts as a short circuit; if OFF, current is zero and acts as an open circuit.
• A diode is a two-terminal device — unlike capacitors (current related to the derivative of voltage) or inductors (derivative of current related to voltage), current in a diode is not linearly related to voltage.
• In a p-n junction, there is a transfer of charge through the junction due to the concentration gradient of charge carriers with the barrier potential.

• A half-wave rectifier uses a single diode, allowing current to flow in one direction, with an AC power source\[V_{ac}\] connected to the diode and a resistor in series.
• Output is discontinuous and pulsating DC - only positive half cycles appear across the load.
• Alternative (negative) half cycles of the AC supply go to waste, making efficiency very low.
• The output waveform shows only the positive side of the sinusoidal cycle, clamping off the negative side.
• Circuit components: transformer (primary & secondary), single diode, and load resistor \[R_L\].
• A transformer is used to step up or step down the AC voltage before rectification.