Photodiode
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A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs
One Ge (top) and three Si (bottom) photodiodes
S604B PhotoTransistor
A one-dimensional photodiode array chip with more than 200 diodes in the line across the center
Diode
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A diode is a two-terminal electronic component that conducts electric current primarily in one direction. It has low resistance in one direction and high resistance in the other.
Close-up view of a silicon diode. The anode is on the right side; the cathode is on the left side (where it is marked with a black band). The square silicon crystal can be seen between the two leads.
A high power vacuum tube diode used in radio equipment as a rectifier
Various semiconductor diodes. Left: A four-diode bridge rectifier. Next to it is a 1N4148 signal diode. On the far right is a Zener diode. In most diodes, a white or black painted band identifies the cathode into which electrons will flow when the diode is conducting. Electron flow is the reverse of conventional current flow.
A vacuum tube containing two power diodes