Diode is an electronic device having conductor at their ends. The principle behind the diode is similar to a valve or a gate, which lets electricity flow only in one direction (Simple English Wikipedia, Diode). Application of diodes is broad. They serve as converter from alternating current to direct current, met at the power supplies. Also they can be used in radio equipment to decode amplitude modulation. Nowadays, there are two basic semiconductor materials which the diode is made from: silicon and germanium Two types of semiconductors are joined to each other to produce semiconductor diode. One of them has spare holes (p side), and the other has extra electrons (n side). This results in the flow of electrons from the side, where there are more electrons to the side where there are less of them, i.e. current. However, it is difficult to flow for the current in the reverse direction. Connecting electrodes are following: positive p-side is anode, and negative n-side is cathode.