Which two important processes occur during the formation of a $p-n$ junction?

When a $P-N$ junction is reverse biased,then ...

$A$ diode is connected to $220 \, V \, (rms) \, ac$ in series with a capacitor as shown in the figure. The voltage across the capacitor is

In a forward-biased $P-N$ junction diode,how does the potential barrier behave?

In a $p-n$ junction diode, the current $I$ can be expressed as $I=I_{0} \left[\exp \left(\frac{e V}{k_{B} T}\right)-1\right]$, where $I_{0}$ is the reverse saturation current, $V$ is the voltage across the diode (positive for forward bias, negative for reverse bias), $I$ is the current through the diode, $k_{B}$ is the Boltzmann constant $(8.6 \times 10^{-5} \; eV/K)$, and $T$ is the absolute temperature. If for a given diode $I_{0}=5 \times 10^{-12} \; A$ and $T=300 \; K$, then:
$(a)$ What will be the forward current at a forward voltage of $0.6 \; V$?
$(b)$ What will be the increase in the current if the voltage across the diode is increased to $0.7 \; V$?
$(c)$ What is the dynamic resistance?
$(d)$ What will be the current if reverse bias voltage changes from $1 \; V$ to $2 \; V$?

The circuit shown contains a $12 \, V$ battery,a $4 \, \Omega$ resistor,and two branches in parallel,each containing an ideal diode and a resistor. Branch $1$ has diode $D_1$ and a $3 \, \Omega$ resistor,while branch $2$ has diode $D_2$ and a $2 \, \Omega$ resistor. Determine the current flowing through the circuit. (in $, A$)