As we all know, generally the diodes are two terminals of uni-directional semiconductor devices.
The diode is just an electronic switch! depending on the voltage difference between the terminals we can utilize the diode function. the starting diode only performs when the anode potential is greater than the cathode potential by the forward falling voltage itself.For ex: diode made of silicon. then drop forward voltage.
If the potential of the anode and the diode cathode are Va and Vk respectively. Assuming a pn diode connection, there is an area near the intersection where the cellular charge carriers all migrate to the other side of the junction. the electrons move to fill the empty holes in the p-type and the holes move to the excess electrons in the n-type. this leaves a ‘depletion zone’ near the intersection without cellular payload carriers . the depletion region is the insulator – since no load carriers are available.
The excess electrons of the n-type have gone to the p-type, leaving the overall positive charge charge (from unmatched protons in the nucleus). as well as the excess pits of the p-type have gone to the n-type, leaving the overall negative charge charge. this bulk cost sets up the potential for contact, which depends on the material. this is often cited as 0.3 v for germanium, 0.7 v for silicon, although the actual value is somewhat smaller. contact potential is a barrier that prevents current flow, ‘potential barrier’. some mobile payload operators have enough energy to overcome the opposite potential.
If the external voltage is applied with the n-type made positive, the p-type is made negative, the depletion layer is amplified. there is a small transient current flow as the moving charge carriers are attracted in the depletion layer from deeper in large quantities, leaving a wider depletion layer. the only flow that flows regularly is from the thermally produced moving carriers in the depletion layer. this current will be small. diode ‘turned off’. (if the voltage is high enough, other effects come into play, see ‘zener diode’, ‘avalanche diode’)
If the external voltage is applied with a positive p-type, the n-type is made negative, the depletion layer is eroded. there is a small transient current flow as the moving charge carriers are attracted to the depletion layer from deeper in large quantities, leaving a narrower depletion layer. as long as the depletion layer is difficult for the mobile payload operator to cross and the current is small, the diode is still ‘switched off’. However, since the applied external voltage approximates the contact potential some load carriers will have enough thermally generated energy to overcome the now lesser current barrier and the small current flowing. the diode is partially illuminated. the current increases exponentially as the voltage rises. if the applied voltage is much greater than the contact potential, the depletion layer disappears, the potential barrier collapses and the diode is fully turned on. through many currents.
So the vi characteristic of a pn junction diode has 3 main parts, reverse bias = off, strong forward = forward, small forward bias = not sufficiently switched off.
There is another type of ‘rectifier’ diode, for example a shottky diode with an n-metal junction or a vacuum diode. Their characteristics differ in detail because physics is different. they share the same pattern, reverse = off, forward = on, gray area near zero bias that is off or inactive.