When you draw diodes, the symbol clearly indicates the direction of forward current flow. You don’t really need names for the two terminals, but if you want to know, they are the Anode and Cathode.
When the diode is reverse biased (the anode connected to a negative voltage and the cathode to a positive voltage), as shown in Fig. 2.0.6, positive holes are attracted towards the negative voltage on the anode and away from the junction. Likewise the negative electrons are attracted away from the junction towards the positive voltage applied to the cathode. This action leaves a greater area at the junction without any charge carriers (either positive holes or negative electrons) as the depletion layer widens. Because the junction area is now depleted of charge carriers it acts as an insulator, and as higher voltages are applied in reverse polarity, the depletion layer becomes wider still as more charge carriers away from the junction. The diode will not conduct with a reverse voltage (a reverse bias) applied, apart from a very small ‘Reverse Leakage Current’ (IR), which in silicon diodes is typically less than 25nA. However if the applied voltage reaches a value called the ‘Reverse Breakdown Voltage’ (VRRM) current in the reverse direction increases dramatically to a point where, if the current is not limited in some way, the diode will be destroyed.
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