Photocurrent is the
electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
through a
photosensitive Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light. In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity. ...
device, such as a
photodiode
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 photons. This can be used for detection and me ...
, as the result of exposure to
radiant power. The photocurrent may occur as a result of the
photoelectric
The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physic ...
, photoemissive, or
photovoltaic effect
The photovoltaic effect is the generation of voltage and electric current in a material upon exposure to light. It is a physical phenomenon.
The photovoltaic effect is closely related to the photoelectric effect. For both phenomena, light is a ...
. The photocurrent may be enhanced by internal
gain caused by interaction among ions and photons under the influence of applied fields, such as occurs in an
avalanche photodiode
An avalanche photodiode (APD) is a highly sensitive type of photodiode, which in general are semiconductor diodes that convert light into electricity via the photovoltaic effect. APDs use materials and a structure optimised for operating with high ...
(APD).
When a suitable radiation is used, the photoelectric current is directly proportional to intensity of radiation and increases with the increase in
accelerating potential till the stage is reached when photo-current becomes maximum and does not increase with further increase in accelerating potential. The highest (maximum) value of the photo-current is called
saturation current
The saturation current (or scale current), more accurately the reverse saturation current, is the part of the reverse current in a semiconductor diode caused by diffusion of minority carriers from the neutral regions to the depletion region. This ...
. The value of retarding potential at which photo-current becomes zero is called
cut-off voltage or stopping potential for the given frequency of the incident ray.
Photovoltaics
The generation of a photocurrent forms the basis of the
photovoltaic cell
A solar cell, also known as a photovoltaic cell (PV cell), is an electronic device that converts the energy of light directly into electricity by means of the photovoltaic effect. .
Photocurrent spectroscopy
A characterization technique called photocurrent spectroscopy (PCS), also known as photoconductivity spectroscopy, is widely used for studying optoelectronic properties of semiconductors and other light absorbing materials.
[
] The setup of the technique involves having a semiconductor contacted with electrodes allowing for application of an electric bias, while at the same time a tunable light source incident with a given specific wavelength (energy) and power, usually pulsed by a mechanical chopper.
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][
]
The quantity measured is the electrical response of the circuit, coupled with the spectrograph obtained by varying the incident light energy by a
monochromator
A monochromator is an optics, optical device that transmits a mechanically selectable narrow band of wavelengths of light or other radiation chosen from a wider range of wavelengths available at the input. The name is .
Uses
A device that can ...
. The circuit and optics are coupled by use of a
lock-in amplifier. The measurements give information related to the band gap of the semiconductor, allowing for identification of various charge transitions like
exciton
An exciton is a bound state of an electron and an electron hole which are attracted to each other by the electrostatic Coulomb's law, Coulomb force resulting from their opposite charges. It is an electrically neutral quasiparticle regarded as ...
and
trion energies. This is highly relevant for studying semiconductor nanostructures like quantum wells, and other
nanomaterials
Nanomaterials describe, in principle, chemical substances or materials of which a single unit is sized (in at least one dimension) between 1 and 100 nm (the usual definition of nanoscale).
Nanomaterials research takes a materials science ...
like
transition metal dichalcogenide monolayers.
Furthermore, by using a piezo stage to vary the lateral position of the semiconductor with micron precision, one can generate a micrograph false color image of the spectra for different positions. This is called scanning photocurrent microscopy (SPCM).
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]
See also
*
Photoconductivity
Photoconductivity is an optical and electrical phenomenon in which a material becomes more electrically conductive due to the absorption of electromagnetic radiation such as visible light, ultraviolet light, infrared light, or gamma radiation.
...
*
Transient photocurrent (TPC)
References
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Electromagnetism
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