current-voltage characteristicsof a CdS photo resistor
• Mohammad abdalraheem• Edward nixson• Awad osman• Mohammed abdala• Osman salah
Objects of theexperiments Measuring the photocurrent I Ph as a function of the voltage U at a constant irradiance . Measuring the photocurrent I Ph as a function of the irradiance at a constant voltage U.
Photocurrent ? a stream of electrons released froma photoelectric cell by the action oflight.
CONTENTS : Introduction photoresistor Current–voltage characteristic Polarization of light Setup Mechanism of photo resistor Result Conclusion
Introduction: A photoresistor is made of a high resistance semiconductor. depends on the amount of light incident upon it. Photo resistors are:used to make light-sensitive devices often made from cadmium sulfide (CdS).
The resistance of a CdS photoresistor varies inversely to the amountof light incident upon it. Its resistance will be higher at lowlight levels (in the dark) and lower athigh light levels (in the light).
Cadmium sulfide is the inorganic compound withthe formula CdS. It occurs in nature with two different crystalstructures. As a compound that is easy to isolate and purify, it is the principal source of cadmium for allcommercial applications.
Model of an ideal photoconductor: electron-hole pairs are produced throughout the crystal by theexternal light source and undergo recombination.Electrons leaving the crystal at the electrode (+) arereplaced with electrons entering at the electrode (-).
D : transparency when thepolarization planes areparallelØ : The irradianceØ 0: irradiance withoutpolarization filterscos2∞: the anglebetween the polarizer
The CdS photo resistor behaves like an ohmicresistance that depends on the irradiance.The photocurrent I ph as a function of thevoltage u at constant irradiance was measuring.The photocurrent I ph as a function of theirradiance at constant voltage u was measuring.