Which type of diode allows current to flow in only one direction?

A rectifier diode is specifically designed to allow current to flow in only one direction, which is its primary function. When alternating current (AC) is applied to a circuit that includes a rectifier diode, it will conduct current during the positive half of the cycle while blocking it during the negative half. This unidirectional flow effectively converts AC to direct current (DC), making rectifier diodes essential components in power supply applications.

The other types of diodes listed serve different purposes. A Zener diode is designed for voltage regulation and can conduct current in both directions under certain conditions, specifically reverse bias at its breakdown voltage. A light-emitting diode (LED) emits light when forward biased and also allows current to flow in one direction, but its main function is to produce light rather than to rectify current. A Schottky diode, known for its fast switching speeds and low forward voltage drop, also allows current to flow in one direction, but it is often used in high-frequency applications rather than standard rectification processes. While they are all diodes, the rectifier diode is the one specifically tailored for the primary function of current rectification.