CBSE Class 12 Physics: p-n Junction Diode Biasing
Step 1 (Circuit Configuration): [1 Mark]
- Forward Biasing: The p-region is connected to the positive terminal and the n-region to the negative terminal of the external DC source. This reduces the depletion layer width.
- Reverse Biasing: The p-region is connected to the negative terminal and the n-region to the positive terminal. This increases the depletion layer width.
Diagrammatic Representation:
Forward Bias: (p-side) ---[+ Battery -]--- (n-side)
Reverse Bias: (p-side) ---[- Battery +]--- (n-side)
Step 2 (I-V Characteristics): [0.5 Mark]
The I-V characteristic curve represents the current $I$ as a function of voltage $V$.
- Forward Bias: Current increases exponentially after the cut-in voltage ($V_{\gamma} \approx 0.3\,\text{V}$ for Ge, $0.7\,\text{V}$ for Si).
- Reverse Bias: A very small constant reverse saturation current ($I_s$) flows due to minority charge carriers, until the breakdown voltage ($V_{BR}$) is reached.
Step 3 (Final Concluded Answer): [0.5 Mark]
The graphical representation is plotted on a Cartesian plane where the x-axis represents Voltage ($V$) and the y-axis represents Current ($I$):
$$I = I_0 \left( e^{\frac{eV}{nkT}} - 1 \right)$$Where $I_0$ is the reverse saturation current, $V$ is the applied bias voltage, and $T$ is the absolute temperature. The graph shows a non-linear, asymmetric behavior confirming the diode acts as a one-way valve for current.
💡 EL10 Concept Insight: Think of a p-n junction like a turnstile at a park: forward biasing pushes the gate open so people (electrons) can walk through easily, while reverse biasing locks the gate tight, letting only a tiny trickle of people sneak through the cracks.