PN Junction Diode Forward Bias

Forward-Biased PN Junction

• When a forward-bias voltage is applied, the potential barrier is lowered, allowing holes from the p region and electrons from the n region to flow across the junction.
• Boundary conditions are derived for minority carrier hole concentration in the n region at the space charge edge and minority carrier electron concentration in the p region at the space charge edge.
• Injected holes in the n region and electrons in the p region become excess minority carriers.

Excess Minority Carrier Behavior

• The behavior of excess minority carriers is described by the ambipolar transport equation developed in Chapter 6.
• Solving the ambipolar transport equation and using the boundary conditions, steady-state minority carrier hole and electron concentrations in the n region and p region are derived.

Minority Carrier Diffusion Currents

• Gradients exist in minority carrier hole and electron concentrations, resulting in minority carrier diffusion currents in the pn junction.
• These diffusion currents yield the ideal current-voltage relationship of the pn junction diode.

Reverse-Biased PN Junction

• Excess carriers are generated in the space charge region of a reverse-biased pn junction.
• These carriers are swept out by the electric field, creating the reverse-biased generation current, another component of the reverse-biased diode current.