The depletion region of a $p-n$ junction:

Consider a $p-n$ junction as a capacitor, formed with $p$ and $n$-materials acting as thin metal electrodes and depletion layer width acting as separation between them. Basing on this, assume that an $n-p-n$ transistor is working as an amplifier in $CE$ configuration. If $C_1$ and $C_2$ are the base-emitter and collector-emitter junction capacitances, then :

Current $I$ through a given $p-n$ junction when a voltage $V$ is applied across it is given by $I = I_0 \left( e^{\frac{V}{2 V_T}} - 1 \right)$, where $I_0$ and $V_T$ are constants. If $r_d(I)$ is the dynamic resistance of the junction, then $r_d(1000 I_0) = \alpha r_d(10 I_0)$, where $\alpha$ is approximately equal to

In a $PN-$junction diode:

When and why is a $p-n$ junction called forward biased? Describe the changes that occur under such bias.

The reason for current flow in a $P-N$ junction in forward bias is