p-n Junction Diode under Forward Bias

Connecting the bias. In forward bias, the external battery's positive terminal is connected to the p-side of the junction and its negative terminal to the n-side -- i.e. the applied voltage is connected in the SAME sense the majority carriers would naturally want to flow, and in OPPOSITION to the junction's own built-in field (Section 9.9).

Narrowing the depletion region. The applied field drives majority holes on the p-side toward the junction, and majority electrons on the n-side toward the junction, from both directions opposing the built-in field. This pushes some of the fixed ions' exposed charge back into neutrality, effectively NARROWING the depletion region and reducing the net potential barrier the carriers must cross. Provided the applied voltage exceeds a small threshold (the barrier potential $V_0$ of Section 9.9, roughly $0.6$-$0.7\ \text{V}$ for a silicon diode -- the KNEE or CUT-IN voltage of its characteristic curve), the barrier becomes low enough that a large number of majority carriers can cross the junction each second. …