What direction does electric current flow through a semiconductor in an LED?

In a Light Emitting Diode (LED), electric current flows in only one direction due to the nature of how semiconductors are structured and operate. An LED consists of two types of semiconductor materials: n-type and p-type. The n-type semiconductor contains an abundance of electrons, while the p-type semiconductor has many holes (places where electrons can go). When a voltage is applied across the LED, electrons from the n-side move towards the p-side, filling the holes. This movement of electrons across the junction constitutes the flow of electric current.

Since current flows from the area of excess negative charge (the n-type) to the area of excess positive charge (the p-type), it establishes a clear path for current to follow, thus ensuring that it only flows in one direction. This unidirectional behavior is a fundamental characteristic of diodes, including LEDs, and is crucial for their operation in electronic circuits. When current is allowed to flow in this single direction, it also leads to the recombination of electrons and holes, resulting in the emission of light—hence the term "Light Emitting Diode."

The other possible directions of current suggested in the options do not apply to LEDs due to their diode properties, which prevent backflow