2015-08-21
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Fig.3.2. Point-contact diode
Thus the characteristic curve of a crystal diode is, as a whole, nonlinear since its resistance in the negative region is much higher than that in the positive region. The simple equation is following from the theoretical analysis of a p-n junction. It describes the current-voltage characteristic of a semiconductor diode at the forward and reverse voltages:
,
where 
is the reverse current of saturation; 
is the thermal potential (at room temperature 
).
At U >> 26mV, 
becomes much higher than the unity ( >> 1), so we can disregard the unity. Then, the forward part of an ideal semiconductor diode characteristic will be described with the following equation:
.
Under high reverse voltage the barrier layer of the p-n junction breaks down and reverse current increases. The layer resistance becomes so small that with increasing current the voltage remains constant and then starts to decrease (the dash line). When the diode is in operation reverse current should not exceed values at which the p-n junction is overheated.
