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Photoconductivity
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<h2 id="applications">Applications</h2> <p class="note">Further information: <a href="/facts/Photoresistor/HBzHNaas">Photoresistor</a></p> <p>When a photoconductive material is connected as part of a circuit, it functions as a <a href="/facts/Resistor/JrsGReM6">resistor</a> whose <a href="/facts/Electrical_resistance/hxSt0UAj">resistance</a> depends on the <a href="/facts/Intensity_(physics)/KFWkJkJI">light intensity</a>. In this context, the material is called a <a href="/facts/Photoresistor/HBzHNaas">photoresistor</a> (also called <i>light-dependent resistor</i> or <i>photoconductor</i>). The most common application of photoresistors is as <a href="/facts/Photodetector/7cSkXS6s">photodetectors</a>, i.e. devices that measure light intensity. Photoresistors are not the <i>only</i> type of photodetector—other types include <a href="/facts/Charge-coupled_device/l6xffIcz">charge-coupled devices</a> (CCDs), <a href="/facts/Photodiode/152Rpk06">photodiodes</a> and <a href="/facts/Phototransistor/152Rpk06">phototransistors</a>—but they are among the most common. Some photodetector applications in which photoresistors are often used include camera light meters, street lights, clock radios, <a href="/facts/Infrared_detector/pK7SfsEv">infrared detectors</a>, nanophotonic systems and low-dimensional photo-sensors devices.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p> <h2 id="sensitization">Sensitization</h2> <p>Sensitization is an important engineering procedure to amplify the response of photoconductive materials.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> 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 <a href="/facts/Albert_Rose_(physicist)/A9ITVLSy">Albert Rose</a> is the work of reference for sensitization.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> <h2 id="negative-photoconductivity">Negative photoconductivity</h2> <p>Some materials exhibit deterioration in photoconductivity upon exposure to illumination.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> One prominent example is <a href="/facts/Hydrogenated_amorphous_silicon/lVNN0bv7">hydrogenated amorphous silicon</a> (a-Si:H) in which a metastable reduction in photoconductivity is observable<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> (see <a href="/facts/Staebler%25E2%2580%2593Wronski_effect/loSYHu9A">Staebler–Wronski effect</a>). Other materials that were reported to exhibit negative photoconductivity include <a href="/facts/Zinc_oxide/P7sTyDez">ZnO nanowires</a>,<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> <a href="/facts/Molybdenum_disulfide/4TRft6Ua">molybdenum disulfide</a>,<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> <a href="/facts/Graphene/QDGUBaPt">graphene</a>,<a class="footnote-ref" id="fnref:17" href="#fn:17"><sup>17</sup></a> <a href="/facts/Indium_arsenide/GMhtPVbU">indium arsenide</a> <a href="/facts/Nanowire/Ege0K9Ek">nanowires</a>,<a class="footnote-ref" id="fnref:18" href="#fn:18"><sup>18</sup></a> decorated carbon nanotubes,<a class="footnote-ref" id="fnref:19" href="#fn:19"><sup>19</sup></a> and metal <a href="/facts/Nanoparticle/k8kNxX4E">nanoparticles</a>.<a class="footnote-ref" id="fnref:20" href="#fn:20"><sup>20</sup></a> </p><p>Under an applied AC voltage and upon UV illumination, <a href="/facts/Zinc_oxide/P7sTyDez">ZnO</a> <a href="/facts/Nanowire/Ege0K9Ek">nanowires</a> exhibit a continuous transition from positive to negative photoconductivity as a function of the AC frequency.<a class="footnote-ref" id="fnref:21" href="#fn:21"><sup>21</sup></a> ZnO nanowires also display a frequency-driven <a href="/facts/Metal-insulator_transition/gay8Tusb">metal-insulator transition</a> at room temperature. The responsible mechanism for both transitions has been attributed to a competition between bulk conduction and surface conduction.<a class="footnote-ref" id="fnref:22" href="#fn:22"><sup>22</sup></a> The frequency-driven bulk-to-surface transition of conductivity is expected to be a generic character of semiconductor nanostructures with the large <a href="/facts/Surface-area-to-volume_ratio/lEl1rKLh">surface-to-volume ratio</a>. </p> <h2 id="magnetic-photoconductivity">Magnetic photoconductivity</h2> <p>In 2016 it was demonstrated that in some photoconductive material a magnetic order can exist.<a class="footnote-ref" id="fnref:23" href="#fn:23"><sup>23</sup></a> One prominent example is CH3NH3(Mn:Pb)I3. In this material a light induced magnetization melting was also demonstrated<a class="footnote-ref" id="fnref:24" href="#fn:24"><sup>24</sup></a> thus could be used in magneto optical devices and data storage. </p> <h2 id="photoconductivity-spectroscopy">Photoconductivity spectroscopy</h2> <p class="note">Main article: <a href="/facts/Photocurrent/e8JdCyGU">Photocurrent § Photocurrent spectroscopy</a></p> <p>The characterization technique called photoconductivity spectroscopy (also known as photocurrent spectroscopy) is widely used in studying optoelectronic properties of semiconductors.<a class="footnote-ref" id="fnref:25" href="#fn:25"><sup>25</sup></a><a class="footnote-ref" id="fnref:26" href="#fn:26"><sup>26</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Photodiode/152Rpk06">Photodiode</a></li> <li><a href="/facts/Photoresistor/HBzHNaas">Photoresistor</a> (LDR)</li> <li><a href="/facts/Photocurrent/e8JdCyGU">Photocurrent</a></li> <li><a href="/facts/Photoconductive_polymer/DVFGluxF">Photoconductive polymer</a></li> <li><a href="/facts/Infrared_detector/pK7SfsEv">Infrared detector</a> <ul><li><a href="/facts/Lead_selenide/66h19tQ2">Lead selenide</a> (PbSe)</li> <li><a href="/facts/Indium_antimonide/76EPwVLC">Indium antimonide</a> (InSb)</li></ul></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>DeWerd, L. 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