Distinguish between intrinsic and extrinsic semiconductors, and explain the biasing of a diode and its effects.

Here are the answers to the questions from the image:

1. (a) (i) Distinguish between intrinsic and extrinsic semiconductors.

• Intrinsic semiconductors are pure semiconductor materials (e.g., silicon or germanium) with no added impurities. Their conductivity is low and depends solely on thermally generated electron-hole pairs.
• Extrinsic semiconductors are intrinsic semiconductors that have been doped with impurities to increase their conductivity. They can be n-type (doped with donor impurities, having excess electrons) or p-type (doped with acceptor impurities, having excess holes).

1. (a) (ii) What do you understand by biasing a diode? Explain the effect of this process on the diode.

• Biasing a diode refers to applying an external voltage across the diode to control the width of its depletion region and thus its conductivity.
• Effect of biasing:
  • Forward bias: When the positive terminal of the voltage source is connected to the p-type material and the negative terminal to the n-type material, the depletion region narrows. This allows current to flow easily through the diode once the forward voltage exceeds the diode's threshold voltage (e.g., $0.7 \text{ V}$ for silicon).
  • Reverse bias: When the positive terminal of the voltage source is connected to the n-type material and the negative terminal to the p-type material, the depletion region widens. This significantly increases the resistance, preventing current flow (except for a very small leakage current) until the breakdown voltage is reached.

1. (b) (i) State in words and in form of a truth table the action of a NAND Logic gate.

• In words: A NAND gate produces an output of 0 (LOW) only if all of its inputs are 1 (HIGH). If any input is 0 (LOW), the output will be 1 (HIGH). It is the inverse of an AND gate.
• Truth Table for a 2-input NAND gate: $$\begin{array}{|c|c|c|} \hline \text{Input A} & \text{Input B} & \text{Output Y} \\ \hline 0 & 0 & 1 \\ 0 & 1 & 1 \\ 1 & 0 & 1 \\ 1 & 1 & 0 \\ \hline \end{array}$$

1. (b) (ii) Draw a circuit diagram with two switches as input and a bulb as the output to illustrate the action of an AND gate.
An AND gate requires all inputs to be HIGH (ON) for the output to be HIGH (ON). This can be illustrated by two switches connected in series with a bulb and a power source.

• Circuit Diagram:

  +V ----[Switch A]----[Switch B]----(Bulb)---- GND
  

  Copy

  (Imagine a battery or power supply connected across +V and GND)

• Explanation:

  • If Switch A is OFF (0) and Switch B is OFF (0), the circuit is open, and the bulb is OFF (0).
  • If Switch A is OFF (0) and Switch B is ON (1), the circuit is open, and the bulb is OFF (0).
  • If Switch A is ON (1) and Switch B is OFF (0), the circuit is open, and the bulb is OFF (0).
  • If Switch A is ON (1) and Switch B is ON (1), the circuit is closed, and the bulb is ON (1).

This demonstrates that the bulb (output) will only light up (be ON) if both Switch A AND Switch B are ON.