Consider the nMOS for simplicity, even in saturation, Ids
grows with Vds
because the depletion region around the drain grows too with Vds
and then the effective length of the channel is shorter.
What i don't understand is that, why we consider the depletion region around the drain a good conductor ?
For example, usually we want to work with a Vgs
higher than Vt
so that the channel is 'filled of' electrons (0 < Vgs < Vt
we have that the channel is made by a depletion region and we just have some leakage of current...! but we don't use the MOSFET in this region...)