These questions ask you to think through the physical reasons behind the diode o

Question

These questions ask you to think through the physical reasons behind the diode operation and the current voltage relationship. In forward bias does drift or diffusion current dominate the diode operation? Why? In reverse bias does drift or diffusion current dominate the diode operation? Why? At zero bias, what is true about the drift and diffusion currents? In forward bias the diode current increases exponentially with voltage. Explain why this is the case in three or four sentences. In reverse bias (before breakdown) the diode current is constant. Explain why this is the case in two or three sentences.

Explanation / Answer

In semiconductors current is due electons and holes movement. This movement of electrons and holes was because of drift and diffusion movement of electrons and hole. Drift movement because of electric field and diffusion movement due variation of doping concentration.

a) In forward bias drift current dominates the diode operation. This is because that diffusion is due to concentration difference when diode is formed this concentration difference creates barrier junction which is known as neutral state. when forward voltage applied across the diode then the current flow due electric field which is known as drift current.

b) In reverse bias again concentration need to be neutalize thus diffusion current dominates the diode current.

c) At zero potential the dirft current is zero and difffuse current will be until formation of junction.

d) In forward bias the current increases exponentially with forward voltage increases until knee voltage this is because the the drift movement of electrons and holes will be opposed by junction barrier.

e) In reverse bias the the potential barrier at junction increase which opposes the movement of majority carriers, only minor carriers cross the junction which is very small and constant.

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