Semiconductor Electronics - p-n Junction Diode

A $p-n$ junction is formed when a $p$-type semiconductor is joined with an $n$-type semiconductor. Two processes occur: diffusion and drift.

The depletion region is a thin layer at the junction devoid of mobile charge carriers (electrons and holes), consisting only of immobile ions. Its thickness is approximately $10^{-6}$ m.

Barrier Potential ($V_b$) is the internal electric field created by immobile ions that opposes the further diffusion of majority carriers. For Silicon, $V_b \approx 0.7$ V and for Germanium, $V_b \approx 0.3$ V.

In Forward Bias, the $p$-side is connected to the positive terminal and $n$-side to the negative terminal. This reduces the depletion layer width and the effective barrier height, allowing current to flow.

In Reverse Bias, the $p$-side is connected to the negative terminal and $n$-side to the positive terminal. This increases the depletion layer width and barrier height, resulting in a very small (negligible) current called reverse saturation current.

A Rectifier is a device that converts AC to DC. A Half-wave rectifier uses one diode and conducts during only one half-cycle of the AC input. A Full-wave rectifier uses two diodes (center-tap) or four (bridge) and conducts during both half-cycles.

The output frequency of a half-wave rectifier is the same as the input frequency ($f_{out} = f_{in}$), whereas for a full-wave rectifier, it is double ($f_{out} = 2f_{in}$).