In electronics, a diode is a twa-terminal electronic component wi asymmetric conductance, it haes law (ideally zero) resistance tae current flow in ane direction, an heich (ideally infinite) resistance in the ither. A semiconductor diode, the maist common type the day, is a crystalline piece o semiconductor material wi a p–n junction connectit tae twa electrical terminals. A vacuum tube diode haes twa electrodes, a plate (anode) an a heatit cathode. Semiconductor diodes wur the first semiconductor electronic devices. The discovery o crystals' rectifyin abilities wis made bi German pheesicist Ferdinand Braun in 1874. The first semiconductor diodes, cried cat's whisker diodes, developed aroond 1906, wur made o mineral crystals such as galena. The day maist diodes are made o silicon, but ither semiconductors such as selenium or germanium are sometimes uised.