Write a short note on a semiconductor diode.

(N/A) semiconductor diode is a basic electronic device formed by joining a $p$-type semiconductor with an $n$-type semiconductor. This junction is provided with two metallic contacts for external connections,hence it is called a $p-n$ junction diode. This structure is illustrated in figure $(a)$.
The circuit symbol for a $p-n$ junction diode is shown in figure $(b)$.
The arrow head in the symbol indicates the conventional direction of current flow when the diode is under forward bias.
The equilibrium barrier potential across the junction can be modified by applying an external voltage $V$ across the diode terminals.