# Diffusion current

When I was talking about external electric field and its action on the diffusion current I was talking about Resistance's one but it appears it is an internal resistance no electric field is present like a normal resistor. But reading Fundamentals of Microelectronics by Behzad Razavi and in its introduction of semiconductor, P and N Semiconductors( Or region) acts like a normal resistor (External electric field is applied to make a drift current inside it). But when mentioning about the diode, he only talks about drift current due to internal electric field of the depletion region of the diode. That's why I was asking about the resistance of the P and N region and Im still confused lol...

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I don't know what did you conclude from that textbook, but participation of drift current in forward biased conducting mode of a diode is minimal. The field in the depletion region is difference between applied field (due to external voltage) and the preexisting (built in) field of the junction. As the field is reduced, reduced is the barrier to the diffusion of carriers from one side of the junction to the other. This increases the diffusion current. The drift current changes very little becouse the depletion region is reduced only slightly and the number of minority carriers swept across the junction changes insignificantly.

ok thank you now it is clear. Can you tell me what kind of resistance exist in a diode other then the resistance in the P and N Region. I was confused because the P and N region acts like a resistor that's why so it requires an electric field like a normal resistor to conduct the current(it is mentioned in the book also see the pic). But other than the resistance of the P and N Junction what else do we have to make the total resistance nonlinear?

In a classical p-n junction designed diode almost all of the applied voltage in a forward biased conduction mode drops across the depletion region. That's becouse the conductivity of the depletion region is much,much lower than in the rest of a diode due to limited number of carriers in the depletion region. Therefore, most of diode's resistance is the resistance of the depletion region: forward voltage drop around 0.7 V is practicaly drop across the junction. Power diodes have a higher voltage drop (1-1.5 V) becouse they are engineered for high currents and part of the voltage drop occurs across the rest of the silicon body, contact resistance silicon-metal etc.

tonyjk
In a classical p-n junction designed diode almost all of the applied voltage in a forward biased conduction mode drops across the depletion region. That's becouse the conductivity of the depletion region is much,much lower than in the rest of a diode due to limited number of carriers in the depletion region. Therefore, most of diode's resistance is the resistance of the depletion region: forward voltage drop around 0.7 V is practicaly drop across the junction. Power diodes have a higher voltage drop (1-1.5 V) becouse they are engineered for high currents and part of the voltage drop occurs across the rest of the silicon body, contact resistance silicon-metal etc.
Hello again,

The resistance of the depletion region is due to the electric field? or it act like a resistor by dissipating energy as heat?