(a) Majority and Minority Charge Carriers: [1 Mark]
- n-type semiconductor: Electrons are the majority charge carriers, and holes are the minority charge carriers.
- p-type semiconductor: Holes are the majority charge carriers, and electrons are the minority charge carriers.
(b) Movement of Charge Carriers in Forward Bias: [1 Mark]
When a p-n junction is forward biased (p-side connected to positive terminal, n-side to negative terminal):
- The applied electric field opposes the internal barrier potential, reducing the depletion region width.
- Holes from the p-region are pushed towards the junction into the n-region, and electrons from the n-region are pushed towards the junction into the p-region.
- This injection of charge carriers across the junction constitutes the forward current.
(c) Estimation of Dynamic Resistance: [1 Mark]
Step 1 (Formula / Governing Law): [1/3 Mark]
The dynamic resistance ($r_d$) of a p-n junction diode is defined as the reciprocal of the slope of the $I-V$ characteristic curve:
$$r_d = \frac{\Delta V}{\Delta I}$$Step 2 (Step-by-Step Mathematical Working): [1/3 Mark]
To estimate the dynamic resistance at $V = -0.6\text{ V}$ (assuming the provided graph shows a typical reverse saturation region or a specific point on the curve):
Identify two points $(V_1, I_1)$ and $(V_2, I_2)$ very close to $V = -0.6\text{ V}$ on the tangent of the curve.
Assuming the change in voltage $\Delta V = V_2 - V_1$ and the corresponding change in current $\Delta I = I_2 - I_1$:
$$r_d = \frac{V_2 - V_1}{I_2 - I_1}$$*(Note: In a standard examination context, students must read the values directly from the provided graph coordinates at the specified voltage point).*
Step 3 (Final Concluded Answer): [1/3 Mark]
After substituting the values from the graph, the dynamic resistance is expressed in Ohms ($\Omega$).
$$r_d = \text{Calculated Value } \Omega$$💡 EL10 Concept Insight:
Think of dynamic resistance like a "traffic flow" gauge; just as it's harder to push through a crowded hallway than an empty one, the diode's resistance changes depending on how much voltage you apply, which is why we measure the slope of the graph rather than just dividing one number by another.