Diode or p-n Junction - Forward Bias

When an external voltage V is applied across a semiconductor diode such that the p-type is connected to +ve terminal and n-type to -ve terminal of battery (in general p-type to high voltage and n-type to low voltage), the diode is said to be forward biased.

\[V_{eff}=V_b-V\]

Where:

• \[V_b\] = potential barrier voltage
• V = applied external voltage

\[I=I_e+I_h\]

Where:

• \[I_e\]​ = electron current
• \[I_h\]​ = hole current

• In forward bias, the depletion layer becomes thin and the forward current increases strongly after the KNEE point.
• The resistance of an ideal diode in forward bias is zero.
• If external voltage (V) is greater than barrier voltage, majority carriers diffuse across the junction, constituting diffusion current \[I=I_e+I_h\].
• Knee voltage for Germanium (Ge) ≈ 0.3 V and for Silicon (Si) ≈ 0.7 V.
• Electrons and holes freely cross the junction in forward bias, leading to a diffusion current opposite to the reverse saturation current.
• As forward bias increases, the effective barrier reduces to \[V_b - V\], allowing more carriers to cross.