Correct Answer

Concept & PrincipleElectricalElectronics

Option C

Is decreased

Quick Summary: Increasing the doping concentration in a semiconductor diode reduces the width of the depletion region. This high doping level increases the intensity of the electric field within the depletion layer, which leads to a lower breakdown voltage.

💡 Explanation

Increasing the doping concentration in a semiconductor diode reduces the width of the depletion region. This high doping level increases the intensity of the electric field within the depletion layer, which leads to a lower breakdown voltage.

🔢 Key Formulas

$W = \sqrt{\frac{2\epsilon}{q} \left( \frac{N_a + N_d}{N_a N_d} \right) V_{bi}}$ — Depletion layer width formula

$E_{max} = \frac{2V}{W}$ — Electric field intensity at the junction

⚙️ Working Principle

The breakdown voltage is inversely related to the doping density. When doping is increased, the width of the depletion layer $W$ decreases according to $W \propto \frac{1}{\sqrt{N_d + N_a}}$ . As the depletion layer narrows, the electric field intensity $E = \frac{V}{W}$ increases for a given reverse bias voltage, causing Zener breakdown to occur at a significantly lower potential.

📌 Key Points

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Heavily doped diodes exhibit Zener breakdown at low voltages.
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Lightly doped diodes (like standard rectifiers) typically undergo Avalanche breakdown at higher voltages.
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The depletion width narrows as doping levels rise, facilitating easier tunneling of charge carriers.
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Breakdown voltage is highly dependent on the net impurity concentration on both sides of the junction.

✅ Advantages

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Allows for precise voltage regulation (Zener Diodes).
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Enables compact circuit design for surge protection.

❌ Disadvantages / Limitations

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Increased doping can lead to higher reverse leakage currents.
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High temperature sensitivity in breakdown performance.

🛠️ Applications / Uses

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Voltage regulators
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Voltage reference circuits
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Surge protection devices

📄 Additional Information

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For typical Zener diodes, doping is very high to ensure a sharp, low-voltage breakdown characteristic.
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Option B is incorrect because increasing doping restricts the space-charge region, causing breakdown to occur sooner (at lower voltage), not later.

📊 Diagram / Illustration

✅

C is correct — Increasing the doping concentration narrows the depletion layer, which enhances the electric field and lowers the reverse breakdown voltage.

Core Concepts Used

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Semiconductor Doping Depletion Region Zener vs Avalanche Breakdown Electric Field Intensity

💡 EXAM TIP

Remember that $V_{br} \propto \frac{1}{N}$ ; always correlate depletion width with doping density to solve any junction-related breakdown questions.

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