It is a physical phenomenon in which light irradiates certain substances and changes the conductive properties of the substance, which can be divided into three categories: external photoelectric effect, internal photoelectric effect and photogenerated volt effect. The external photoelectric effect refers to the physical phenomenon in which electrons in an object escape from the surface of an object under the action of light and emit outward. Photons are a description of electromagnetic waves in the visible light band in the form of quantized "particles". A photon has energy hv, h is Planck's constant, and v is the optical frequency. The photon flux corresponds to the light intensity. The external photoelectric effect is described by Einstein's photoelectric effect equation:
Ek =hν -W
where h is Planck's constant and ν is the frequency of incident light). The external photoelectric effect can only occur when the photon energy is equal to or greater than the work of escape. Therefore, each object has an optical frequency threshold corresponding to the photoelectric effect, called the red limit frequency. For incident light above the red-limited frequency, the exogenous photocurrent is proportional to the light intensity. The internal photoelectric effect is further divided into two categories: the photoconductive effect and the photogenerated volt effect. The photoconductivity effect refers to the phenomenon that the electrons in the bandgap of a semiconductor material are excited by photons with an energy not lower than the bandgap width and jump to the conduction band, thereby increasing the conductivity. The wavelength of the photon whose energy corresponds to the bandgap width is called the critical wavelength of the photoconductive effect. The photovoltaic effect refers to the phenomenon that the action of light can cause semiconductor materials to produce electromotive force in a certain direction. The photovoltaic effect can be further divided into barrier effect (junction photoelectric effect) and lateral photoelectric effect. The mechanism of the barrier effect is that in the contact region (or PN junction) between the metal and the semiconductor, the electrons are excited by photons to break away from the constraints of the barrier (or bandgap) and generate electron-hole pairs, and the electrons move to the outside of the N region and the holes move to the outside of the P region under the action of the electric field in the barrier layer, forming a photogenerated electromotive force. The lateral photoelectric effect is a phenomenon in which the concentration of electron-hole pairs generated by light excitation is also uneven, and the electrons diffuse to the unirradiated part, resulting in positive charge in the illuminated part and negative charge in the unilluminated part.
External photoelectric effect
photons, photon energy; photoelectron
The external photoelectric effect refers to the phenomenon that electrons in an object escape from the surface of an object and emit outward under the action of light.
Internal photoelectric effect
Under the action of light, the conductivity of the object changes or the effect of photogenerated electromotive force is generated
Photoconductive Effects: Photoresistors, Photodiodes (Transistors)
Photogenerated volt effect: photocell
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