undergraduate

A very basic experiment with Semiconductor Diodes

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Diode is a two terminal electronics component which has low resistance to current in one direction but very high resistance in opposite direction. Today the most common type of diode is the one which has crystalline piece of semiconductor with a P-N junction connected to two terminals. Diodes do not follow ohm’s law. So its important to study their Current-Voltage characteristics (I-V curves). In this experiment we do exactly that. From these curves we find some important quantities like ideality factor and knee voltage. Ideality factor, also known as the quality factor  accounts for carrier recombination as the charge carriers cross the depletion region. The ideality factor ‘n’ typically varies from 1 to 2 (though can in some cases be higher), depending on the fabrication proce ss and semiconductor material and in many cases is assumed to be approximately equal to 1

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Knee voltage is the voltage at which current through the diode is 1mA. It is a measure of how much energy is needed to push electrons through the diode. Temperature dependence of knee voltage is determined by placing the diode in thermal contact with hot water and allowing it to cool down. Knee voltage at different temperatures is determined and plotted in a graph (refer the pdf). From this graph we find out that knee voltage decreases with increasing temperature.  The equations used are written below and all data has been compiled in a pdf.

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