Image of a laser photodiode

P–n photodiodes are used in similar applications to other, such as, (CCD), and tubes. They may be used to generate an output which is dependent upon the illumination (analog for measurement), or to change the state of circuitry (digital, either for control and switching or for digital signal processing). Photodiodes are used in devices such as players,,. The simple laser diode structure described above is inefficient. Such devices require so much power that they can only achieve pulsed operation without damage. Although historically important and easy to explain, such devices are not practical. In these devices, a layer of low- material is sandwiched between two high-bandgap layers. One commonly used pair of materials is (GaAs) with.