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 spectrum, ultraviolet light, infrared light, or gamma rays.
When light is absorbed by a material such as a semiconductor, the number of free electrons and Electron hole increases, resulting in increased electrical conductivity.
Classic examples of photoconductive materials include:
Molecular photoconductors include organic,
inorganic,
and – more rarely – coordination compounds.
Applications
When a photoconductive material is connected as part of a circuit, it functions as a
resistor whose resistance depends on the light intensity. In this context, the material is called a
photoresistor (also called
light-dependent resistor or
photoconductor). The most common application of photoresistors is as
, i.e. devices that measure light intensity. Photoresistors are not the
only type of photodetector—other types include charge-coupled devices (CCDs),
and
—but they are among the most common. Some photodetector applications in which photoresistors are often used include camera light meters, street lights, clock radios, infrared detectors, nanophotonic systems and low-dimensional photo-sensors devices.
Sensitization
Sensitization is an important engineering procedure to amplify the response of photoconductive materials.
The photoconductive gain is proportional to the lifetime of photo-excited carriers (either electrons or holes). Sensitization involves intentional impurity doping that saturates native recombination centers with a short characteristic lifetime, and replacing these centers with new recombination centers having a longer lifetime. This procedure, when done correctly, results in an increase in the photoconductive gain of several orders of magnitude and is used in the production of commercial photoconductive devices. The text by Albert Rose is the work of reference for sensitization.
Negative photoconductivity
Some materials exhibit deterioration in photoconductivity upon exposure to illumination.
One prominent example is hydrogenated amorphous silicon (a-Si:H) in which a metastable reduction in photoconductivity is observable
(see Staebler–Wronski effect). Other materials that were reported to exhibit negative photoconductivity include
Zinc oxide,
molybdenum disulfide,
,
,
decorated carbon nanotubes,
and metal
.
Under an applied AC voltage and upon UV illumination, Zinc oxide Nanowire exhibit a continuous transition from positive to negative photoconductivity as a function of the AC frequency.
Magnetic photoconductivity
In 2016 it was demonstrated that in some photoconductive material a magnetic order can exist.
One prominent example is CH
3NH
3(Mn:Pb)I
3. In this material a light induced magnetization melting was also demonstrated
thus could be used in magneto optical devices and data storage.
Photoconductivity spectroscopy
The characterization technique called
photoconductivity spectroscopy (also known as
photocurrent spectroscopy) is widely used in studying optoelectronic properties of semiconductors.
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See also
