8 Most VSAQ’s of Semiconductor Electronics: Materials, Devices and Simple Circuits Chapter in Inter 2nd Year Physics (TS/AP)
2 Marks
VSAQ-1 : What are intrinsic and extrinsic semiconductors?
Intrinsic Semiconductor
- Intrinsic semiconductors are pure semiconducting materials with no intentional impurities.
- They contain a single-element crystalline structure, such as silicon or germanium.
- Intrinsic semiconductors generate charge carriers (electrons and holes) through thermal excitation.
- Their conductivity increases with temperature as more charge carriers are created.
- At absolute zero, they act as insulators, and at higher temperatures, they become conductive.
Extrinsic Semiconductor
- Extrinsic semiconductors are intentionally doped with specific impurities to modify their electrical properties.
- Doping introduces foreign atoms, either donors (e.g., phosphorus) or acceptors (e.g., boron), into the semiconductor lattice.
- Extrinsic semiconductors have a controlled concentration of charge carriers, making them more conductive than intrinsic semiconductors.
- They can be n-type (donor-doped) or p-type (acceptor-doped), depending on the dopant used.
- Doping allows tailoring the electrical behavior of semiconductors for various electronic applications.
VSAQ-2 : What is a p-type semiconductor ? What are the majority and minority charge carriers in it?
A p-type semiconductor is created by adding trivalent impurities like boron to an intrinsic semiconductor. This process generates “holes” in the crystal lattice, which are areas lacking valence electrons. Holes act as the majority charge carriers, carrying a positive charge, while electrons become minority charge carriers. Holes’ movement, driven by an electric field, contributes to the semiconductor’s conductivity. P-type semiconductors are vital in electronic devices and the formation of p-n junctions in components like diodes and transistors, enabling control of current flow.
VSAQ-3 : Draw the circuit symbols for p – n – p and n – p – n transistors.
These symbols represent the common emitter configuration of bipolar junction transistors (BJTs), where the arrow indicates the direction of current flow and the orientation of the arrowhead distinguishes between p-n-p and n-p-n transistors.
VSAQ-4 : In which bias, can a zener diode be used as voltage regulator?
A zener diode is used in reverse bias as a voltage regulator. In this biasing condition, the zener diode operates in the breakdown region, and it maintains a constant voltage across its terminals, even if there are variations in the supply voltage or the load current. This makes it ideal for voltage regulation in electronic circuits. The zener diode will continue to regulate the voltage as long as the current through it remains above the minimum specified value (IZmin) in the reverse breakdown region.
VSAQ-5 : What is p-n junction diode? Define depletion layer.
A p-n junction diode is a semiconductor device formed by joining a p-type semiconductor and an n-type semiconductor together. The contact surface between the two halves is called a p-n junction.
The depletion layer is a thin region on both sides of the p-n junction where the mobile charge carriers (electrons and holes) are depleted, leaving only immobile ions. This depletion of charge carriers creates a potential barrier, preventing further flow of current in the reverse bias direction. It plays a crucial role in the functioning of the p-n junction diode.
VSAQ-6 : Which gates are called universal gates?
NAND and NOR gates are known as universal gates because any Boolean function can be implemented using only these gates. Both NAND and NOR gates can be used to create all other basic logic gates, such as AND, OR, and NOT gates, making them versatile in digital circuit design.
VSAQ-7 : Give example of “photosensitive substances”. Why are they called so?
Photosensitive substances include metals like cadmium, zinc, magnesium, and alkali metals like lithium, sodium, and caesium, which respond to visible light. Photosensitive materials are called so because they can emit photoelectrons when exposed to electromagnetic waves of appropriate wavelengths. The interaction between light and these materials results in the release of electrons, making them sensitive to light. This property finds various applications in fields like photography, solar cells, and optical sensors.
VSAQ-8 : What happens to the width of the depletion layer in a p-n junction diode when it is i) forward biased and ii) reverse biased?
When a p-n junction diode is forward biased, the width of the depletion layer decreases. This is because the positive terminal of the battery is connected to the p-side of the junction, and the negative terminal is connected to the n-side. This causes the free electrons from the n-region and the holes from the p-region to move towards the depletion region, reducing its width.
In the case of reverse biasing, the width of the depletion layer in a p-n junction diode increases. The negative terminal of the battery is connected to the p-side of the junction, and the positive terminal is connected to the n-side. This causes the free electrons from the n-region and the holes from the p-region to move away from the depletion region, resulting in an expansion of its width.