Is the current in reverse biased PN junction due to drift or diffusion?

Question

Wikipedia says

The saturation current (or scale current), more accurately the reverse saturation current, is that part of the reverse current in a semiconductor diode caused by diffusion of minority carriers from the neutral regions to the depletion region.

Another site says: http://www.ece.utep.edu/courses/ee3329/ee3329/Studyguide/ToC/PNdiode/currents.html

When the diode is reverse biased diffusion is negligible, but drift remains constant.

I am confused, should we regard the reverse saturation current as a drift or diffusion current?

I'd be glad if you could explain. Thank you.

Wikipedia:https://en.m.wikipedia.org/wiki/Saturation_current

Answer 1

There is both drift and diffusion in a PN junction diode. Even though their sum is constant throughout the device, the individual components vary spatially. The diffusion current is non-negligible only near the junction (within a few diffusion lengths), current flow is because of drift in all other places.

At V=0, the drift and diffusion components cancel each other to give zero current.

If V>0, the majority carriers (holes from the p-side) are injected across the depletion region to become minority carriers on the other side (holes in n-side). Since the injected carrier concentration is higher than the minority carrier concentration in the neutral region, these carriers diffuse into the neutral region.

In reverse bias (V<0), the carrier injection happens in the other direction. The minority carriers (electrons from p-side) inject to the other side (n-side) to reduce the minority carrier concentration near the junction. This causes diffusion to happen from the neutral region to the depletion region.

Answer 2

In reverse bias mode, for PN junction, current is (majorly) due to drift. When PN junction is in forward bias mode, current is due to diffusion.