These layers form a diode (from the ancient Greek di, for two and ode, for way, or path). If you apply the voltage the other way, the flow is blocked. If you apply voltage so the negative end of the circuit is on the n-type layer, the electrons flow between the two layers easily. To the electron, this junction is like a waterfall: give them a bit of a push one way and they will fall over, but they can't go back up. The combination forms what is called a pn-junction. In the technical language of electronics, one layer is n-type (the one that wants to give them away), while the other is p-type. This contamination means that one layer has lots of high-energy electrons that it wants to give away, while the other layer has spaces for electrons that it really wants to fill at a lower energy level. This is made of two layers of a crystalline material like GaAs that have been contaminated with different materials (chemists call this doping).

Inside an LED bulb is a small semiconductor chip, which is the part that gives off the light.

How the led light works