Why ohms law is not valid for semiconductors?
It is not very clear that resistance varies with voltage and voltage is still directly praportional to current to the resistance at that particular time. ( it is in fact contrary to ohm’s law which says:
Current is directly praportional to voltage and the constant of praportionality is nothing but the resistance).
I would like to share some conclusions from stastical mechanics here.
Ohm’s law has its theoretical basis in classical physics( Maxwell-Boltzman distribution).
But it has its own limitations. After the development of quantum mechanics, it has been found that, electorns obey Fermi-Dirac distribution law. Which has been applied to semiconductor theories. ( Particles obeying Fermi-Dirac distribution law are called fermions. Electron in one such particle).
Because a semiconductor`s resistance is not fixed. It`s resistance varies with both the amplitude and polarity of the applied Voltage. It is a nonlinear device which makes it appear not to follow Ohms law. A semiconductor (diode) does however adhere to Ohms law. At any specific time the Voltage across the diode is equal to the current through the diode times the resistance of the diode at that specific time. The fact that the diode`s resistance is changing with the amplitude of the applied Voltage makes it appear that the diode does not follow Ohms law. Edit add on: Even a reverse biased diode follows ohms law. The reverse Voltage across a diode at any specific time is equal to the reverse leakage current times the diodes resistance in the reverse direction at that particular time. Even when reverse breakdown occurs (the instantaneous value V) = (the instantaneous value of I) x (the instantaneous value of R).
