Question 3
- Define the term doping with respect to semiconductors.
- State two advantages of transistors over triodes.
- Figure 2 is a schematic diagram of a p-n junction diode.
- Redraw Figure 2, and connect a battery to forward bias the junction.
- State the effect of connecting in 3(c)(i) on the junction width (w).
- Draw and label a circuit symbol of a p-n junction diode.
The expected responses were:
(a) Definition of the term doping
This is the introduction of impurities into an intrinsic semiconductor to modify or change
its electrical properties.
(b) Advantages of transistors over diodes
- Faster response time
- Less heat generation
- More robust
- Portability/less bulky
- Miniature in size/compactness
- Better efficiency
- Lower power consumption
- Cheaper to manufacture
(c) (i) Forward biasing a p-n Junction diode
(ii) Effect of forward biasing the p-n junction on the junction width(w)is:
The width (w) gets thinner/narrower.
(iii) Circuit symbol of a p-n junction diode
The Chief Examiner reported that virtually all the candidates that attempted this question gave the correct definition of doping and majority showed the desired battery connection for forward-biased diode. However, only a few showed understanding of the consequence of the forward bias on depletion layer.