Which semiconductor device only allows current to flow in one direction?

A diode is a semiconductor device specifically designed to allow current to flow in only one direction. This capability is fundamental to its operation and is a result of the p-n junction structure that characterizes diodes. When forward-biased, the diode conducts current, while in reverse bias, it prevents current from flowing, except for a very small leakage current.

This one-way function is crucial in various applications, such as rectification, where alternating current (AC) is converted to direct current (DC). The diode helps to ensure that the flow of current is controlled and directed properly in circuits, making it an essential component in power supplies and signal processing.

In contrast, while devices like thyristors can also control current flow, they operate under different principles and are designed for switching applications rather than simply allowing current in one direction. Transistors serve as amplifiers or switches but do not exclusively restrict current to a single direction. Digital logic gates process signals based on logical operations but do not function as current-controlling devices in the same context as diodes.