#semiconductor devices

p-n Junction, Depletion Region and Diode Characteristics

The reverse bias resistance of a p-n junction diode is typically:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. In reverse bias, the diode allows only a small reverse saturation current ( μ A ), resulting in a very high resistance compared to the low resistance in forward bias. Substituting values gives High, which matches expected behaviour for this semiconductor device configurat

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p-n Junction, Depletion Region and Diode Characteristics

In forward bias, the resistance of a p-n junction diode is:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. In forward bias, the barrier height decreases, allowing significant current (mA) to flow, resulting in low resistance compared to reverse bias, where resistance is high due to minimal curr

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p-n Junction, Depletion Region and Diode Characteristics

The minority carrier injection in a forward-biased diode refers to:

**p-n junction formation** diffusion of holes from p to n and electrons from n to p leaves ionized donors positive on n-side and acceptors negative on p-side, forming space-charge depletion region with electric field directed from n to p (positive to negative), barrier potential V_b ≈0.3 V Ge, 0.7 V Si, opposes further diffusion, drift current due to minority carriers swept by field balances diffusion at equilibrium net current zero. In forward bias, electrons from the n-side cross to the p-side (where they are minority carriers) and holes from the p-side to the n-side, contributing to the dif

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p-n Junction, Depletion Region and Diode Characteristics

The reverse saturation current in a diode is:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. The reverse saturation current is nearly constant with voltage (until breakdown), determined by the minority carrier concentration, not the applied reverse voltage magnitude. Substituting

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