Operation

When a positive voltage is applied to the anode (p side) relative to the cathode (n side), the junction is said to be forward biased, see Figure 70.

**Figure 70:** Forward biased pn junction.
$\begin{figure} \begin{center} \epsfig{file=images/diodeimg4.eps}\end{center}\end{figure}$

The effective barrier potential is reduced by the applied voltage, and majority carriers can flow across the junction. This results in a large current flow. The junction is switched on.

When a negative voltage is applied to the p side (anode) relative to the n (cathode), the junction is said to be reverse biased, see Figure 71. The effective barrier potential is increased by the applied voltage, and only a small minority carrier current flows. To a first approximation this reverse current is zero - the junction is switched off.

**Figure 71:** Reverse biased pn junction.
$\begin{figure} \begin{center} \epsfig{file=images/diodeimg5.eps}\end{center}\end{figure}$

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