I've been told that depletion region width decreases when we increase doping in a P-N junction. But doesn't this contradicts the fact that diffusion current increases with current? I'm probably mixing things up. What I would like to know is:
How does diffusion current varies with doping
How does the width of depletion region varies with doping
How does the charge (and then, the electric field and the voltage) of depletion region varies with doping. Why is it said the voltage cannot increase more than $0.7$ V for a silicon junction?